The Sounding Object

The Sounding Object
Edited by
Davide Rocchesso and Federico Fontana
Edizioni di Mondo Estremo

The Sounding Object
Davide Rocchesso, Editor Università di Verona, Italy
Federico Fontana, Editor Università di Padova and Università di Verona, Italy
Federico Avanzini Università di Padova, Italy
Nicola Bernardini Conservatorio di Padova, Italy
Eoin Brazil University of Limerick, Ireland
Roberto Bresin Kungl Tekniska Högskolan, Stockholm, Sweden
Roberto Burro Università di Udine and Università di Padova, Italy
Soﬁa Dahl Kungl Tekniska Högskolan, Stockholm, Sweden
Mikael Fernström University of Limerick, Ireland
Kjetil Falkenberg Hansen Kungl Tekniska Högskolan, Stockholm, Sweden
Massimo Grassi Università di Udine and Università di Padova, Italy
Bruno Giordano Università di Udine and Università di Padova, Italy
Mark Marshall University of Limerick, Ireland
Breege Moynihan University of Limerick, Ireland
Laura Ottaviani Università di Verona, Italy
Matthias Rath Università di Verona, Italy
Giovanni Bruno Vicario Università di Udine, Italy

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The work described in this book was supported by the European Commission
Future and Emergent Technologies collaborative R&D program under contract
IST-2000-25287 (project SOb - the Sounding Object).
The SOb project web site is http://www.soundobject.org
The book web site is http://www.soundobject.org/SObBook
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Chapter 11
Complex gestural audio
control: the case of
scratching
Kjetil Falkenberg Hansen and Roberto Bresin
Kungl Tekniska Högskolan – Department of Speech, Music, and Hearing
Stockholm, Sweden
hansen@speech.kth.se, roberto.bresin@speech.kth.se
11.1
Introduction
To scratch means to drag a vinyl record forwards and backwards against the
needle on an ordinary turntable along the grooves, not across, though it might
sound like it. This way of producing sounds has during the last two decades
made the turntable become a popular instrument for both solo and ensemble
playing in different musical styles, still mostly in the hip-hop style where Disk
Jockeys (DJs) ﬁrst started to scratch. However, all musical genres seem to
be able to adopt the turntables into their instrumental setups. Composers in
traditions like rock, metal, pop, disco, jazz, experimental music, ﬁlm music,
contemporary music and numerous others have been experimenting with DJs
the past years. Experimental DJs and most hip-hop DJs now frequently call
221

222
The Sounding Object
themselves “turntablists”, and the music style of scratching and extensive cut-
and-paste mixing is called “turntablism”. These terms, derived from the word
turntable, are now generally accepted. It is also generally accepted that a turn-
tablist is a musician and that the turntable is to be considered an instrument.
The acoustics of scratching has been barely studied until now. On the other end
the business market of DJs equipment is quite large. It is therefore interesting
to study the phenomenon of turntablism from a scientiﬁc point of view.
In this chapter three experiments are presented. Aim of these experiments
is to model scratching based on analysis of an experienced performer. For this
purpose scratching as an expressive musical playing-style is looked at from dif-
ferent views. Experiment 1 investigates the musical fundamentals of scratch-
ing, and explains the most common playing-techniques in more detail. Experi-
ment 2 investigates a real performance with aid of sensors on the equipment in
order to understand what kinds of problems and parameter variation a model
will need to deal with. Experiment 3 investigates what happens to the record
that is being scratched, as it is apparent that some heavy damage will be done
to the vinyl and this can therefore affect the sound quality.
11.1.1
Common set-up for experiments
All the experiments shared part of the equipment and methods, as explained
in this section. Setups and methods speciﬁc to each experiment are explained
in the respective sections.
11.1.2
Method
In all the experiments presented in the following, the same method was
used. Small exceptions in the equipment are presented in Table 11.11.
Subject
Only one subject performed during experiments 1 and 2, examining ex-
pressive playing. He is Alexander Danielsson, DJ 1210 Jazz, a professional
DJ from Sweden. He volunteered for the experiments. 1210 Jazz (as he will
be called throughout the paper) has no formal musical training, but has for al-
most 15 years been considered to be among the best turntablists in Sweden and
Europe, a reputation he has defended in DJ-battles (as competitions for DJs
1The audio recorded in Experiment 2 was only intended to illustrate what happened to the
sound, and acoustical properties were not analyzed in this investigation.

Chapter 11. Complex gestural audio control: the case of scratching
223
Equipment
Description
Turntable
Technics SL-1210 Mk2 with felt slip-mat
Cartridge
Stanton 500 (Experiment 1 only) and Shure M44-7
DJ-mixer
Vestax PMC-06 Pro
Faders
Vestax PMC-05 Pro
Record
1210 Jazz - Book of Five Scratches. Book 2 [125]
Potentiometer
Bourns 3856A-282-103A 10K (Experiment 2 only)
DAT-recorders
Teac RD-200T
Channel 1 (20 kHz)
Potentiometer
Multichannel
Channel 2 (10 kHz)
Crossfader
(Exp. 2 only)
Channel 3 (10 kHz)
Sound
Sony TCD-D10
2 channels (44.1 kHz)
(Exp. 1 and 3)
Wave analysis
Soundswell Signal Workstation [64]
software
Wavesurfer [221]
Table 11.1: Equipment used for the experiments.
are called) as well as on recordings, in concerts, and in radio and television
appearances. He has made three records for DJ use, so-called battle records,
one of which was used during the recording sessions.
For experiment 3, the ﬁrst author performed the test.
Material
All the recordings used in these experiments were done at KTH during
2001. The equipment used for the experiments is summarized in Table 11.1.
Instrument line-up
Mixer and turntable were placed in a normal playing-fashion with the mixer
to the left. The turntable was connected to stereo-in on the mixer. The right
channel was output to a DAT recorder, while the left channel was output to a
headphone mixer so the DJ could hear himself. See Figure 11.1.
Calibration
We needed to have a turntable with constant rotation speed for the experi-
ments. The spikes (labelled 1-10 in Figure 11.2) in the waveform in the lower

224
The Sounding Object
Figure 11.1: Instrument set-up with mixer on the left and turntable on the right
side.
Figure 11.2: Calibration of turntable motor. The upper panel shows the record
angle in degrees from the potentiometer. The lower panel shows the waveform
from a prepared vinyl record.
panel come from a cut made across the record, marking every 360◦ with a pop.
Since the distance between each spike was equal, the turntable motor by as-
sumption generates a constant speed. The upper panel in Figure 11.2 shows
the readout from a 10-rounds potentiometer in degrees.

Chapter 11. Complex gestural audio control: the case of scratching
225
11.1.3
Background - Playing the turntable
Introduction to scratch music
Turntablism includes both scratching, using one turntable, and beatjug-
gling, using two turntables. Scratching is a typical solo-playing style, com-
parable to that of electric guitar. The musician expresses himself in intricate
rhythmical and in tonal structures. Beatjuggling sometimes has a rhythmical
backing function to hip-hop rapping, but is also often played in expressive
solo-acts, typically with a groove on one turntable. A history of turntablism
and overview of the practice of using turntables as instruments has been repor-
ted in a previous paper [114].
In the early eighties, scratching DJs and the entire hip-hop community got
the attention of the record-buying generation, gradually spreading their sounds
to the rest of the musical world. Since then, DJs have appeared on recordings
by artists as diverse as John Zorn [259], Herbie Hancock [112], Mr Bungle
[41], Portishead [196], David Byrne [45] and Tom Waits [248]. The ﬁrst exper-
iments with use of phonograph to create music started about 1915 and were car-
ried on through the next three decades by Stephan Wolpe, Paul Hindemith, Ern-
est Toch, Percy Grainger, Edgar Varèse, Darius Milhaud and Laszlo Moholy-
Nagy [56]. None of these composers were turntable artists, nor did they write
compositions for turntable that still exist (although some compositions may be
reproduced by memory). John Cage [47] and Pierre Schaeffer [213] composed
what are considered to be the ﬁrst pieces for turntables, but they are recognized
mainly for their approach to sounds, not to the turntable. Pierre Schaeffer’s
concept of musique concrete is as much a result of tape-manipulation as vinyl-
manipulation, and his practices would probably have been commenced even
without the phonograph technology [107, 136].
Instrumentalists must learn to incorporate a variety of techniques and meth-
ods for tone manipulation in their playing, and DJs have established a funda-
mental ground with an almost compulsory assortment of techniques [115]. All
new ways of playing and scratching are persistently explained and debated on,
especially on Internet discussion forums on sites devoted to turntablism [215].
Some of the accepted techniques will be described and analyzed in Experiment
1. Numerous techniques more or less resemble, and often originate, from those
described, but they will not be included in this study. Many ways to scratch do
not ﬁt into the general scheme, and are not widely used. They are, however, all
explained on turntablism Internet sites as soon as they surface. The overview
in Experiment 1 will not deal with the more unconventional scratches.

226
The Sounding Object
11.1.4
Equipment and instruments
Any turntable might be used for scratching, but the standard is a direct-
driven machine with the platter mounted on the motor. Scratching also utilizes
an audio mixer with a volume control that is mostly used for controlling the
onsets and offsets of tones. Therefore, the turntable as a musical instrument
includes the turntable with pick-up, slip-mat, mixer and a vinyl record. Relat-
ively few manufacturers have succeeded to enter the market with highly qualit-
ative equipment, considering the massive interest in DJing and the prospective
of good sales. Turntablists seem to be skeptical to adapt to radical innova-
tions, especially those that oversimplify and trivialize playing. One example
is the production of a mixer that allows for some of the hardest techniques to
be played with ease. This particular mixer, Vestax Samurai [241], never got
much positive attention from the professionals, even though it could inspire to
the development of new techniques. Why this is so and which consequences
this inﬂict on the evolution of the scene would bring us to an extensive dis-
cussion. In brief, displacement technology could be considered to cheapen the
musician’s skill, and this explains the hesitation to switch to such a technology
[104].
Low budget equipment fails to convince users. At a professional level there
are several brands to choose from, that have comparable qualities. The stand-
ard line-up for many turntablists is a set made of two Technics SL-1200 Mk2
turntables with Shure M44-7 pick-ups, and a scratch mixer without unneces-
sary controllers, e.g. the Vestax PMC-06 Pro. In the following, “Technics”
will refer to the Technics SL-1200 Mk2 or its black counterpart SL-1210 Mk2.
Normally this equipment is organized with one turntable placed on either side
of the mixer, and even rotated 90◦ with the tone-arms away from the body to
avoid hitting the tone-arm with a botched arm movement.
The quartz direct-driven Technics (Figure 11.3) has advantages to the belt-
driven turntables in terms of pick-up speed and motor strength (the starting
torque of a Technics is 1.5 kg/cm). When pushing the start-button, a mere
third of a revolution (0.7 s) is needed to reach full speed at 33 1 revolutions per
3
minute (rpm), and stopping the record goes even faster [224].
With a felt slip-mat lying between the platter and the record, moving the
record in both directions with the motor on and the platter still going is fairly
easy. In rougher moves and when maintaining a heavier touch, the platter might
follow the record movement, but because of the pick-up speed, that is not a
problem.
The pick-up mechanism is specially designed for scratching to prevent the

Chapter 11. Complex gestural audio control: the case of scratching
227
Figure 11.3: Technics SL-1200 Mk2 turntable (SL-1200 is silver gray and SL-
1210 is black).
diamond stylus tip from skipping from one groove to another, and even the
stylus tip is designed to make scratching easier. “Needle” is the popular term
for both the stylus tip and the bar or tube that holds it, called the cantilever.
Normal high ﬁdelity styli are often elliptical at the end to follow the groove
better, while scratch styli are spherical and made stronger as the force on the
needle can get so high that both the reels and the needle are in hazard of be-
ing damaged. An M44-7 can handle three times the tracking force (the force
holding the needle in the groove) of the hi-ﬁ cartridge Shure V15 VxMR—up
to 3.0 g (grams) on the M44-7 compared to 1.00 g on the V15 [220]. Out-
put voltage from the scratch cartridges is 3-4 times higher (9.5 mV) than the
hi-ﬁ cartridge. The hi-ﬁ cartridge has better frequency response, from 10 to
25 000 Hz, compared to M44-7’s 20 to 17 000 Hz. On scratch cartridges the
cantilever holding the stylus has high mass and stiffness, and the high fre-
quency range is much affected and poorly reproduced. M44-7 has twice the
cantilever diameter compared to the V15.
The mixer, see Figure 11.4, has other features than just amplifying, the
most important ones are the volume controls and fader. DJ mixers were ori-
ginally designed for switching smoothly between two turntable decks when
doing beat mixing2, and all mixers have for both stereo channels at least a
volume fader and tone controls (bass, mid and treble ranges). The fader was de-
veloped during the late seventies to make beat mixing easier, and is positioned
2Eventually, better mixers allowed the traditional beat mixing of two different songs to evolve
into the practise of making one section of a record last for as long as wanted by cross mixing
between two identical records

228
The Sounding Object
Figure 11.4: Rane TTM56 scratch mixer with a close-up on crossfader and
volume controls.
at the front end of the mixer. In Figure 11.4 the close-up shows crossfader and
volume faders.
The crossfader glides seamlessly from letting in sound from channel 1 (left
turntable), through mixing signals from channel 1 and channel 2, to channel 2
(right turntable) only. Whether a left-positioned crossfader shall let in sound
from the left or right turntable is now adjustable with a special switch called
hamster switch. Fading curves for crossfader and volume faders can be cus-
tomized on most mixers. Several varieties in how the crossfader operates are
fabricated, such as using optics or Rane’s non-contact magnetic faders [198].
“Fader” might, however, be a misguiding term as the fading curve on the cross-
fader normally is adjusted to be very steep, making it act as an on-off switch.
Any vinyl record might be used for scratching, but during the last ten years
sounds with certain qualities have dominated. Only fragments of original re-
cordings are being manipulated, often shorter than one second. Isolated mu-
sical incidents like drumbeats, guitar chords, orchestra hits and especially sung,
spoken or shouted words represent the majority of sounds used. To simplify
playing, and for obvious economical reasons, a number of popular sounds are
compiled on one record pressed for DJ use, commonly called a battle record
(copyrighting is understandably an abiding but disconcerting question). The
sound samples come without long gaps in one track. Longer sentences are
often scratched one word or syllable at the time.
Sounds can be given different onsets and offsets depending on the tech-
nique used by the DJ. These variations on the sounds and the results of dif-

Chapter 11. Complex gestural audio control: the case of scratching
229
ferent techniques applied to the sounds will be described and analyzed in the
following section presenting the Experiment 1.
11.2
Experiment 1 - The techniques of scratching
11.2.1
Introduction
The aim of this ﬁrst experiment was to investigate and explain some of the
different scratch techniques.
11.2.2
Method
Material
DJ 1210 Jazz was asked to perform some typical techniques, both inde-
pendently and in a natural musical demonstration, and he also included more
unusual examples. Further he was restricted to one frequently used sound, the
breathy-sounding Fab Five Freddie “ahhh”-sample from “Change the beat”(a
chorused voice sings “ahhh” with a falling glissando in the end [81]). The
recordings lasted for about 30 minutes, out of which long sections (several
seconds) of continuous playing of a single technique were extracted. About
twenty different techniques were recorded in this session.
11.2.3
Techniques
Basic movements
Basic DJ hand movements are naturally distinguished in two separate en-
tities; record movement and mixer (crossfader) movement. Most scratching
techniques derive from fast but rather simple movements. Record control and
mixer control depend strongly on one another, analogous to right- and left-
hand movements in guitar playing. Both hands can operate on both devices,
and most players switch hands effortlessly, both for playing purpose and for
visual showing-off purpose. Even techniques where both hands go to the same
device are performed. A general rule has been to have the strong hand on the
vinyl, but with a more intricate use of crossfader, learners now tend to use their
strong hand on the mixer instead. The volume controls (ﬁrst and foremost the
crossfader) are handled with ﬁngertips and are often bounced swiftly between
the thumb and the index ﬁnger. The record is pushed forwards and backwards

230
The Sounding Object
Figure 11.5: 8 ways of starting and ending a movement over a sound on the
record.
in every imaginable manner. Travelling distance for the vinyl varies from less
than 10◦ to more than 90◦ in each direction.
Onsets and offsets depend on the position of the sample when starting a
scratch, the use of crossfader, and the speed of the movement. Three funda-
mentally different onsets are possible to achieve. First, a scratch movement
can start before the sound sample, and the acceleration then completes before
the sound cuts in. The crossfader will have no effect. In the second kind of
onset, the scratch movement starts within the sound sample without use of
the crossfader; the record will speed up from stand still and produce a very
fast glissando from the lower limit of auditory range to desirable pitch, often
above 1 kHz. A third onset category occurs when the crossfader cuts in sound
from within the sample, creating an insigniﬁcant crescendo-effect, as if it was
switched on. Any sound can be deprived of its original attack by cutting away
the start with the crossfader.
Figure 11.5 shows a sector of a record with a sampled sound on it. The
y-axis represents the position in the sample. There are eight different forms
of a forward-backward motion, marked (a)-(h). All movement types are per-
mutations of starting, turning and stopping either within or without the sampled
sound. Movement types (a)-(b) and (e)-(f) start before the sound, and move-
ments (c)-(d) and (g)-(h) start within the sound. Movements (a), (c), (e) and (g)

Chapter 11. Complex gestural audio control: the case of scratching
231
Figure 11.6: Spectrograms of 4 different types of scratch movement.
have the change of direction outside the borders of the sound, while (b), (d), (f)
and (h) change direction within the sound. Movements (a)-(d) end outside the
sound border, while (e)-(h) end before the sound has ﬁnished.
Four of the possible movement types have been generated with the scratch
model described in section 11.A. A simple forward and backward gesture is
applied to a sound ﬁle, producing examples of types (a)-(b) and (g)-(h). Spec-
trograms of these examples are drawn in Figure 11.6, and demonstrates how
the onsets and offsets will vary from each case. The sound used is a ﬂute-like
sound with the fundamental at 500 Hz. Spectrograms are cut at 9 kHz as the
most interesting part is the shape of the fundamental and the added noise band
that simulates groove wearing in the model. All four gestures represented in
the spectrograms are identical.
Besides the starting, turning and stopping points, several other factors have
inﬂuence on the output sound of a simple forward and backward movement:
Direction, or whether to start with a push or a pull, is an effective variable. The
speed changes the pitch, and can be fast or slow, steady or shifting. In addition
to controlling sounds with the record-moving hand, the crossfader gives the DJ
the option to produce alternative onsets and offsets. The kind of sound sample

232
The Sounding Object
Figure 11.7: Waveform (upper panel) and spectrogram (lower panel) of simple
forward and back motion, called baby-scratching
on which all variables are executed greatly affects the result.
Figure 11.7 shows the waveform and spectrogram of the sound being scrat-
ched. All the other ﬁgures presented in the following do not include the wave-
form plot, as the spectrogram contains all information about the interesting
characteristics of the sound examples discussed here. Figure 11.7 is an illus-
tration of a very simple scratch (this speciﬁc one will be explained as baby-
scratching) similar to type (b) in Figure 11.5. The scratch is approximately
0.4 s long and can in traditional musical notation resemble two sixteenth notes
at about 75 bpm (beats per minute). The original sound (“ahhh”) has a noise
band with a broad maximum, inducing the perception of some pitch. Arguably
the ﬁrst sixteenth has a broad maximum around 1200 Hz and the second six-
teenth around 2400 Hz, or an octave higher, but it is hard to establish a deﬁnite
tonal phrase because of the glissando effects that can be observed in the spec-
trogram in Figure 11.7. The ﬁrst sixteenth starts abruptly when the sound cuts
in (this is evident on the amplitude level ﬁgure), while the second sixteenth has
a smoother attack with an increase of both frequency and amplitude.

Chapter 11. Complex gestural audio control: the case of scratching
233
Figure 11.8: Spectrogram of two simple forward and backward movements.
Ending of tones can equally be divided into three categories, with the quick
slowing down to a halt perhaps being the most interesting one. During a scratch
performance, a big portion of the onsets and offsets come from directional
changes of the record movement within the boundaries of a sound sample.
Figure 11.8 shows a combination of movement type (e) followed by type (c)
(see Figure 11.5), where the turns from going forward to backward are made
just beyond the ending of the sound. The 0.8 s long scratch is built up by four
sixteenth notes at 75 bpm. The ﬁrst sixteenth has an abrupt attack, while the
second and fourth sixteenths have a more smooth attack. The third sixteenth
has a faster attack than the second and the fourth, but the sound is still achieved
in the same way. The explanation of these differences lies in the speed of the
turn of record direction. In the example in Figure 11.7, the turn when going
from forward to backward movement is quicker than the turn when going from
backward to forward again—the initial move from the body is faster than the
initial move towards the body. All the endings except the last one are results
of slowing down the record to change the direction, producing a fast drop in
frequency.
The pitch we perceive from the broad maximum of the noise band is de-
termined by the original recording and by the speed by which it is played back.
Normally 33 1 rpm is used for scratching, but also 45 rpm. These numbers
3
can be adjusted by a certain percentage in both directions depending on the
product: a Technics affords a detuning of the rotation speed by at most 8%
[224]. 8% creates a span of almost a musical major sixth (from 30 2 to 48 3 rpm,
3
5
a factor of 1.58). Perceived pitch is most inﬂuenced by the playback speed on
the sample caused by the hand movements. There are no musical restrictions

234
The Sounding Object
Figure 11.9: Different hand positions taken from a performance by DJ 1210
Jazz.
(i.e. tonally or melodically) to which audible frequencies can be used, and no
concerns about preserving the original pitch of the source recording. For a
500 Hz tone to reach 15 kHz, however, playback at 30 times the original speed,
or 1000 rpm, is required, which is impossible for a human DJ to accomplish.
Different source recordings cover the whole frequency range, and may even
exceed the pick-up’s range.
Hand motion
Each DJ has a personal approach to moving the record, even though the aim
is a well-deﬁned technique. There seems to be an agreement among performers
on how it should sound, but not so much on how it is accomplished. Since the
record has a large area for positioning hands and ﬁngers, and the turntable can
be rotated and angled as preferred, the movements can be organized with great
variety (Figure 11.9).
The characteristics of the hand movements associated with different types
of scratches will be examined in a future investigation.

Chapter 11. Complex gestural audio control: the case of scratching
235
Figure 11.10: Spectrogram of tear-scratch.
Without crossfader
The most fundamental technique, also recognized as the ﬁrst scratch, is
done by pushing the record forward and backward, and without using the cross-
fader. When done in a steady rhythmical pattern of for example sixteenth-notes
it is called baby-scratch. Movement types number (b) and (e) and the combina-
tion of (e) and (c) from Figure 11.5 are most frequent in baby-scratching. How
fast the turntablist turns the record direction inﬂuences both attacks and decays.
A long slowdown or start gives a noticeable glissando-like sound. In addition,
the frequency-drop will make the listener experience volume decrease—this is
thoroughly explained by Moore [179]. This evidence can also be extrapolated
from equal loudness contours and Fletcher-Munson diagrams [75, 110].
Another fundamental technique is the tear-scratch that divides one stroke,
usually the backstroke, in two separate strokes. The division is kind of a halt
before returning the sample to the starting point. It is not necessary that the
record stops entirely in the backstroke, but the fall in frequency and volume
will give an impression of a new tone attack. Figure 11.10 shows how the
simple division affects the sound.
Two techniques take advantage of a tremble-motion on the record. Tensing
the muscles on one arm to perform a spasm-like movement is called a scribble-
scratch. Dragging the record with one hand while holding one ﬁnger of the
other hand lightly against the direction, letting it bounce on the record, make a
stuttering sound called hydroplane-scratch.

236
The Sounding Object
Figure 11.11: Spectrogram of hydroplane-scratch.
Both hydroplane- and scribble-scratches produce continuous breaks in the
sound. On a spectrogram of a hydroplane-scratch, Figure 11.11, it is possible
from the tops and valleys around 1 kHz to trace how the ﬁnger bounces on the
vinyl. The slowdowns at a frequent rate, here about 30 per second, produce a
humming sound. The broad maximum makes jumps of about 1 kHz in these
slowdowns.
With crossfader
The volume controls can cut a sound in or out at will, which was also
the technique behind the experiments of Pierre Schaeffer conducted during the
early ﬁfties [191]. He discovered that when removing the attack of a recorded
bell sound, the tone characteristics could change to that of a church organ, for
instance. Normally the turntablists let the crossfader abruptly cut the sound,
in this way cutting the transition. The sound can easily be turned on and off
several times per second, making the scratches sound very fast. This is prob-
ably one reason why scratching sounds so recognizable and inimitable. Some
techniques are just baby-scratching with varying treatment of the crossfader.
Others use longer strokes with quick crossfader cutting.
Forwards and backwards, chops and stabs all hide one of the two sounds
in a baby-scratch, either the forward push or the backward pull. In chirps
only two snippets of sounds are heard from a very fast baby-scratch. On every
movement forward, the fader closes fast after the start, cutting the sound out,
and going backwards only the last bit of the sound is included (cut in). At these
points of the scratch, the vinyl speed is high and so the broad maximum of the
noise band is high, 2 kHz in Figure 11.12. The drawn line, adapted from the
baby-scratch spectrogram in Figure 11.7, shows the probable broad maximum
curve of the forward and backward movement with 0.1 s silenced, hiding the

Chapter 11. Complex gestural audio control: the case of scratching
237
Figure 11.12: Spectrogram of chirp-scratch. The overimposed grey curved-line
shows the assumed record movement.
change of record direction.
The most debated technique is the ﬂare-scratch, with all its variations. Flar-
ing means cutting out sound during the stroke, but discussions among the per-
formers concern how many times and how regular these cuts should occur. In
a relatively slow forward movement that starts with the sound on, the sound
is quickly clicked off and back on by bouncing the crossfader between thumb
and index ﬁnger. Various ﬂares are given names based on the number of such
clicks. A 2-click ﬂare is one stroke with two clicks, or sound-gaps, producing a
total of three onsets. An orbit or orbit ﬂare is the same type of scratch on both
forward and backward strokes. In a 2-click orbit ﬂare there will be a total of
six onsets; three on the forward stroke, one when the record changes direction
and two on the backward stroke. The ﬂaring-technique generates many other
techniques.
Twiddle and crab further take advantage of the possibility to bounce the
light crossfader between thumb and other ﬁngers, making a rapid series of
clicks. The superﬁcial similarity with the tremolo in ﬂamenco-guitar is evident.
Figure 11.13 comes from a twiddle, where the index and middle ﬁngers on the
left hand thrust the crossfader on the thumb. The short gaps are easily audible
even in a very short scratch.
Because the numerous clicks are done in one single stroke, the frequency

238
The Sounding Object
Figure 11.13: Spectrogram of twiddle scratch.
Figure 11.14: Spectrogram of transformer-scratch.
of each attack or tone will be quite stable. Roughly speaking, ﬂutter-tongue
playing on brass instruments and ﬂutes produces a similar sound [175].
The old technique called transformer-scratch is often compared to strobe
lights, as the crossfader is pushed on and off fast and rhythmically during rel-
atively long and slow strokes, or even at original playback speed. Now trans-
forming is often performed with varying but simple rhythmical patterns on the
crossfader, and thus controlling the record speed can be given more attention.
Transforming generally attains greater tonal variety than the techniques where
the main musical purpose is producing short tones by rapid fader clicks, as, for
instance, it happens in the twiddle-scratch. Figure 11.14 shows a spectrogram
of a typical transformer-scratch section.

Chapter 11. Complex gestural audio control: the case of scratching
239
11.2.4
Discussion: Relevance in music
Techniques are seldom played individually for longer periods; conversely
they are blended and intertwined for greater expression and musical substance.
For instance, it might be difﬁcult to distinguish one technique from the other
during a two-click ﬂare-scratch and a twiddle-scratch in succession. Indeed,
the turntablists do not want to emphasize this. Rather, they often refer to the
different playing styles and scratch solos in terms of ﬂow, which, considered
as a whole, seems to be more important than the components. Mastering one
single scratch should be compared to mastering a scale (or, rather, being able to
take advantage of the notes in the scale during a performance) in tonal impro-
visation. Without the sufﬁcient skill, complicated patterns will not sound good
at least to experienced and trained ears. Aspiring DJs, like all other musicians,
have to devote hours to everyday training to get the right timing.
11.3
Experiment 2 - Analysis of a genuine perform-
ance
11.3.1
Introduction
In order to acquire knowledge about how scratching is performed and how
it works and behaves musically, an analysis of several aspects of playing was
necessary. Results from this analysis can be used as a starting point for im-
plementing future scratch-models. By only looking at the individual technique
taken from the musical context, it is easy to get an impression of scratching as
a clean and straightforward matter to deal with. This is not always the case.
Techniques are not often played individually, but rather shortened, abrupted,
and mixed one with the other. Also many gestures are not necessarily classi-
ﬁed as valid techniques, but as variations or combinations of existing ones.
11.3.2
Method
In the DJ 1210 Jazz recording sessions eight performances were executed,
all of which without a backing drum track. Since 1210 Jazz is an experienced
performer, the lack of backing track was not considered a restrictive or unnat-
ural condition even though scratching often is performed to a looped beat.

240
The Sounding Object
Figure 11.15: Potentiometer set-up with top and lateral views of the turntable.
Equipment
A potentiometer was used to track the vinyl movement. The 3 3 rounds
4
10 kOhm potentiometer was mounted to the vinyl with the help of a stand, and
a cylinder attached to the record center. The output was recorded by a mul-
tichannel DAT. The potentiometer was chosen based on how easily it turned.
No effect could be noticed in the performance and friction on the vinyl when it
was attached, and the DJ felt comfortable with the set-up. See Figure 11.15.
Modern mixers give the DJ the opportunity to change the fading curves of
the crossfader. To get a reliable signal we decided to ﬁnd the slider position
from reading the output voltage, not the physical position. Two cables connec-
ted from the circuit board to the multichannel DAT recorder tracked the slider
movement, but not automatically the sound level. The crossfader run is 45 mm,
but the interesting part, from silence to full volume, spans only a distance of
2-3 millimeters, a few millimeters away from the (right) end of the slider run.
Because the crossfader did not respond as the DJ wanted to, he glued a credit
card to the mixer, thus shortening the distance from the right end to where the
crucial part (the so-called cut-in point) is located (see Figure 11.16). Positioned
to the right, the crossfader completely muted all sound, and it let through all
sound when moved a few millimeters (to the left).
Only the right channel of the stereo sound output signal was recorded to the
multichannel DAT, but that was sufﬁcient for evaluating the record movement
output against the sound output. The original sound from the record had no
signiﬁcant stereo effects, and both right and left channel appear similar.

Chapter 11. Complex gestural audio control: the case of scratching
241
Figure 11.16: Crossfader adjustment. The white stapled-square marks the po-
sition occupied by a credit card used to shorten the slider range.
Calibrations
Both the crossfader and the potentiometer had to be calibrated.
To read the approximate sound output level from the position of the cross-
fader, every millimeter position was mapped to a dB level. A problem occurred
as the slider had some backlash (free play in the mechanics). By using two
different methods, both with step-by-step and continuous moving of the cross-
fader, the sound levels on a deﬁned sound (from a tone generator) could be
found and used as calibration for the output level. See Figure 11.17.
The potentiometer had a functional span of about 1220◦ or 3 1 rounds. Un-
2
fortunately it was not strictly linear, but we succeeded in making a correction
to the output values so that the adjusted output showed the correct correspond-
ence between angle and time. See Figure 11.18.
The dotted line in Figure 11.18 is the original reading from the poten-
tiometer doing 3 rotations in 6 seconds, using the same method as for calib-
rating the turntable mentioned earlier. The dashed line is the correction-curve
used to calibrate the readings. The solid line is the corrected original signal
later applied to all recordings. The voltage was adjusted to rounds, expressed
in degrees.
Material
The DJ was asked to play in a normal way, as he would do in an ordinary
improvisation. He was not allowed to use other volume-controllers than the

242
The Sounding Object
Figure 11.17: Crossfader calibration. The X axis shows the whole travelling
distance of the slider in mm.
Figure 11.18: Calibration of potentiometer.
crossfader, but as the crossfader is by far the most used control during in a
performance, and the other controllers are used to achieve the same sounding

Chapter 11. Complex gestural audio control: the case of scratching
243
results, this does not affect the experiment. The performances from that session
were by all means representative examples of improvised solo scratching with
a clearly identiﬁable rhythmic structure; one of those examples is used here. 30
seconds of music were analyzed. All sounds were originated from the popular
“ahhh” sound from “Change the beat” [81]. This sampled part is found on most
battle-records, including the 1210 Jazz [125] record we used.
The analysis was done on the basis of three signals; the crossfader, the
record movement and a waveform of the recorded sound, and for comparison
even the audio track. Comparisons with previous recordings of the separate
techniques provide valuable information on the importance of these techniques.
We decided to describe the music in terms of beats and bars in addition
to looking at time. This description necessarily calls for interpretations, and
especially at the end of the piece it is questionable if the performance is played
strictly metrically or not. In this analysis, however, that is a minor concern.
With our interpretation the piece consist of 12 bars in four-fourth time. The
tempo and rhythm is fairly consistent throughout with an overall tempo of just
under 100 beats per minute. Figure 11.19 shows an excerpt of the readings and
illustrates how the structuring in beats and bars was done. The upper panel is
the low pass-ﬁltered signal from the crossfader in volts, the middle panel is the
audio signal and the lower panel is the potentiometer signal in degrees. This
excerpt is from bar 7.
11.3.3
Measurements outline
Vinyl movement
One of the things we wanted to measure was the movement of the vinyl
record itself without considering the turntable platter or motor. The slip-mat,
placed between the platter and the record, reduces friction depending on the
fabric and material. For these measurements the DJ used his preferred felt
slip-mat, which allowed to move the record quite effortlessly regardless of the
platter and motor movement.
Crossfader movement
The second element we measured was the movement of the crossfader. To
get a reliable signal we measured it directly on the circuit board.

244
The Sounding Object
Figure 11.19: Bar 7 transcribed to musical notation. The grey areas mark
where the crossfader silences the signal. The upper panel is the low pass-
ﬁltered signal from the crossfader in volts, the middle panel is the audio signal,
and the lower panel shows the rotation angle in degrees.
Sound output
The third signal we recorded was the sound output from the manipulated
record. In order to let the musician play in a realistic manner he was allowed
to choose the sound to work with.
11.3.4
Analysis
In the following analysis some key elements will be considered; namely the
work with the vinyl in terms of directional changes, angles and areas, speed and
timing; the activity on the crossfader and the volume; the occurrences of pre-
deﬁned techniques; and ﬁnally the occurrences of different kinds of patterns.
The three variables considered in the measurements are: (1) crossfader move-
ments, (2) record movements, and (3) associated sound signal.

Chapter 11. Complex gestural audio control: the case of scratching
245
Sounding directional changes
Sound is obtained from scratching by moving the record forward and back-
ward. This implies that the record will change direction continuously during
playing. Directional changes can be grouped in three categories:
• changes which are silenced with the crossfader;
• silent changes, where the change happens outside a sound;
• changes where the sound is heard, here called turns.
Turns can be further categorized in terms of signiﬁcant and insigniﬁcant turns,
according to how well we can hear the directional change.
A signiﬁcant turn will produce the attack of the next tone. An insigniﬁcant
turn appears when only a little part of the sound from the returning record is
heard, either intentionally or by imprecision, also producing a kind of attack
(although less audible).
The record direction was changed 135 times, in average 4.5 times per
second. Of such changes, 21.5% were heard: 18.5% of them were signiﬁcant
turns; 6% were insigniﬁcant. A technique like scribble would inﬂuence this
result considerably, as it implies fast and small forward and backward move-
ments (about 20 turns per second) with sound constantly on. This excerpt had
two instances of short scribble-scratches, representing 36% of the signiﬁcant
turns. It seems that in a normal scratch-improvisation (at least for this subject),
about 70-90% of the directional changes are silenced.
Further investigation is needed to explain why so many directional changes
are silenced. More data from other DJs needs to be collected and analyzed.
However, one possible reason could be that the characteristic and recognizable
sound of a record changing direction is no longer a desirable sound among
DJs wanting to express themselves without too much use of clichés. These
characteristic sounds are typically associated with the early, simple techniques.
Angles and area
The length of a sample naturally limits the working area on the record for
the musician, and moving the record forward and backward can be made difﬁ-
cult by the turntable’s tone-arm. About a quarter of the platter area is taken up
by the tone-arm in the worst case. Big movements are difﬁcult to perform fast
with precision, resulting in a narrowing down, as the technical level evolves,
to an average of about 90◦ (although not measured, recordings of DJs from

246
The Sounding Object
mid-eighties seem to show generally longer and slower movements). We con-
sider long movements those that exceed 100◦. A little less than 50% were long
movements.
The occurrence of equally long movements in both directions was quite
low, about 30% of the pairing movements covered the same area. Only 25% of
the forward-backward movements started and ended on the same spot.
Issues concerning rhythm and timing
An attempt to transcribe the piece to traditional notation will necessarily
mean that some subjective decisions and interpretations have to be made. Nev-
ertheless, some information can be seen more easily from a musical analysis.
This transcription allows an analysis of timing in relation to the various scratch-
ing techniques, by looking at both the record and the crossfader speed and their
relation to the corresponding waveform.
Speed
About half of all movements, both forwards and backwards, were done
slower than the original tempo in this recording. The backward moves were
often performed faster than the forwards moves (33% compared to 26%). Due
to different factors, as inertia and muscle control, and the fact that scratching
implies a rounded forward and backward stroke, it is hard to perform a move-
ment with constant speed. Hence, most of the movements have unstable speeds
and do not result in straight lines appearing at the potentiometer output.
Sound position
Even though a DJ has a great control over the record position, in this helped
also by visual marks such as colored stickers, nevertheless a minor inaccuracy
can affect the result greatly. 1210 Jazz had only one sound (and position) to
focus on, so he did not make any serious mistakes resulting in unexpected
attacks or silences. The sound sample was also quite simple to deal with. With
continuous change of sound samples, or with sharper sounds such as drumbeats
and words with two or more syllables, this issue becomes more problematic.
Crossfader
This analysis did not distinguish extensively between crossfader move-
ments done with the hand or by bouncing with the ﬁngers, but some evident

Chapter 11. Complex gestural audio control: the case of scratching
247
cases can be pointed out. It is likely that the crossfader should be left open for
performing a number of certain techniques, but the longest constant openings
in this performance had durations which were shorter than half a second. The
crossfader was turned or clicked on about 170 times in 30 seconds (more than
5 times per second). The total amount of sound and silence was approximately
equal.
53.3% of the draws had one sound only, and 11.8% of the draws were
silenced. Among the remaining draws, 24.4% had two sounds, 6.6% had three
sounds and 3.7% of the draws had four separate sounds. Multiple sounds per
draw were distributed quite evenly on backward and forward draws, except for
the ﬁve draws carrying four tones; all were done on the backward draw.
Techniques
The aesthetics of today’s musicians roots in a mutual understanding and
practice of attentively explained techniques. However, the improvising does
not necessarily turn out to be a series of well-performed techniques. So far,
research on scratching has considered the performing techniques separately.
A run-down on which techniques are used in this piece clearly shows the need
for a new approach considering the combination of techniques and basic move-
ments. All recognized techniques are here associated to the bar number they
appear in. The duration of a bar is approximately 2.5 s, i.e. the DJ played with
a tempo of about 96 bpm.
Forwards appear in the same position in almost every bar. There are 9
forwards in 12 bars; 7 land on the fourth beat (in bars 1, 2, 3, 4, 6, 10 and 12)
and 2 forwards land on the ﬁrst beat (in bars 6 and 9). All forwards on the
fourth beat are followed by a pickup-beat to the next bar, except for the last
forward.
Tear-like ﬁgures occurred from time to time when the sound was clicked
off during the backward draw, but they do not sound as tears because the break-
down in the backward draw was silenced. 3 of these tear-likes are executed,
in bars 6, 10 and 11. Normally, several tears are performed in series, and the
sound is left on all the time. None of the tears here were clean in that sense, or
perhaps even intended to be tears.
Chops normally involve a silenced return. Prior to 10 silences, a chop was
performed. It happened in bars 3, 4, 5, 7, 8 and 11. A chop can be followed
by another technique (but the whole forward move is used by the chop) as it
happened during the experiment in bars 5, 7 and 11.
Stabs and drags are similar to chops, but performed with more force (faster).

248
The Sounding Object
They both appeared in bar 8. Many movements (35%) had a swift crossfader
use. There are two states of crossfader position during scratching: With the
sound initially off, sound is temporarily let in; conversely, with the sound ini-
tially on, the sound is temporarily cut out. Main techniques of sound-off state
are different transform-scratches, while chirps, crabs and especially ﬂares are
typical for sound-on state. Sound-on state should give more signiﬁcant turns.
Most of the signiﬁcant (and insigniﬁcant) turns happened with variations on
the ﬂare scratch.
Some common techniques were not found in the recording of the perform-
ance under analysis, including baby, hydroplane, chirp and tweak. The reasons
for this could be many; baby scratching will often seem old-fashioned while
tweaking can only be performed with the motor turned off, so it is more de-
manding for the performer to incorporate it in a short phrase. The absence of
hydroplane and chirp can be explained as artistic choice or coincidence, as they
are widely used techniques.
Patterns
Some movements and series of movements are repeated frequently. Pat-
terns are not considered to be valid techniques, and they are not necessarily
so-called “combos” either. A combo is a combination of two or more tech-
niques, performed subsequently or simultaneously.
Often a signiﬁcant turn was followed by a silenced change and a new sig-
niﬁcant (or insigniﬁcant) turn in the experiment. This particular sequence was
performed 6 times (in bars 1, 4, 6, 11, 12).
In the performance analyzed only 5 long (more than 100◦) forward strokes
were followed by another long forward stroke, and there were never more than
2 long strokes in a row. On the backward strokes, long strokes happened more
frequently. 16 long strokes were followed by another long stroke; on three
occasions 3 long strokes came in a row, and once 6 long strokes came in a row.
No forward stroke was silenced, while 16 backward strokes were silenced
with the crossfader. As the chop technique involves a silenced return, this
technique was often evident around the silences.
Two bars, bars 4 and 5, started almost identically, the major difference is
that bar 4 had a forward on the fourth beat while bar 5 had a chop on the third
offbeat.

Chapter 11. Complex gestural audio control: the case of scratching
249
Twin peaks
One returning pattern was a long forward stroke with a slightly shorter
backward stroke followed by a new long forward stroke (shorter than the ﬁrst)
and the backward stroke returning to the starting point. This distinctive se-
quence looks in the record angle view like two mountain peaks standing next
to each other, the left one being the highest, and as it returned 8 times in 30
seconds in this experiment, it was for convenience named twin peaks3.
The twin peaks pattern was repeated 8 times with striking similarity. The
ﬁrst peak was the highest in all cases, ranging from 100◦ to 175◦ (132.5◦ in
average) going up, and from 85◦ to 150◦ (120◦ in average) going down. The
second peak ranges from 50◦ to 100◦ (77.5◦ in average) going up, and from
75◦ to 150◦ (128.75◦ in average) going down. All had about 10 crossfader
attacks (from 7 to 11), and more on the second peak than the ﬁrst. The second
peak was always a variant of a ﬂare scratch. The 8 twin peaks-patterns take up
almost one third of the performance in time.
11.3.5
Discussion
The division and structuring of the recording into bars reveals that the tech-
niques are used taking into account timing and rhythmical composition, such
as fourth beats. For a better understanding of musical content in scratching,
more recordings should be analyzed as only 12 bars and one subject do not
sufﬁce for formulating general conclusions.
11.4
Experiment 3 - Wearing of the vinyl
This experiment is a quite simple test to ﬁnd the extent of wearing on a
vinyl record used for scratching. During the ﬁrst minute of scratching, a record
groove will be drastically altered by the needle and start carrying a broad white
noise signal.
11.4.1
Method
On 1210 Jazz’s record [125] there is a set of sounds from Amiga and Com-
modore 64 games. One of these sounds, with a bright ﬂute-like character, has
3After the TV-series by David Lynch called “Twin Peaks”, with a picture of a mountain in the
opening scene.

250
The Sounding Object
a fundamental frequency at 600 Hz and a harmonic spectrum (harmonics at
n·F0). This sound is repeated on the record in a short rhythmic pattern with
small silent gaps.
On the very ﬁrst playback of the record, high-end equipment was used to
ensure highest possible quality. Second playback was done on the equipment
used in the experiments, but with a brand new scratch needle. Third playback,
which is used as reference in this paper, was made with the same needle after
a few weeks of use (which should mean the needle is in close to perfect con-
dition). After playing back the short segment of the record at normal speed,
the record was dragged forward and backward over the sound for one minute,
and then the segment was played back at normal speed again. The forward
and backward movement was done none-expressive at a constant speed and
with approximately 2 cm run on each side of the point on the record. This
procedure was repeated over and over, so the ﬁnal test covers 15 minutes of
scratching (dragging the record forward and backward corresponds to normal
scratch movements) and 15 playbacks of the same sound in different stages of
wearing. All playbacks and scratching was recorded in stereo to DAT at 44 kHz
sample rate.
Noise from the equipment
The noise coming from the equipment (especially the hum from mixer and
turntable) is about 10 dB lower up to 4 kHz than the total noise emitted from a
blank place on the record and the equipment. Figures 11.20 and 11.21 show the
noise level from the record and the equipment with the ﬁrst axis cut at 22 kHz
and 6 kHz respectively.
11.4.2
Results
The following ﬁgures show a selection of the spectrograms and line spec-
trum plots that were taken from every minute of the recording. Deterioration
happens gradually, but only the most illustrating events are included here.
Spectrograms
Figure 11.22 show the original sound with surrounding silence before the
scratching begins, and after 1 , 2 and 15 minutes of scratching. After one
minute of dragging the record forward and backward, the signal clearly has

Chapter 11. Complex gestural audio control: the case of scratching
251
Figure 11.20: Noise levels of recording (upper plot) and equipment (lower
plot).
Figure 11.21: Noise levels of recording (upper plot) and equipment (lower plot)
up to 6 kHz.
deteriorated. Even the silent parts on each side of the sound signal start to
carry a noise signal.
After 2 minutes of scratching, Figure 11.22, the whole surrounding silent
part carries the noise signal. The broad noise band seems to a have higher
level of energy between 2 and 6 kHz. The upper harmonics (from the fourth
harmonic upwards) that could still be seen reasonably clearly after one minute
are from now on masked in the noise signal.

252
The Sounding Object
Figure 11.22: Spectrogram of the tone and surrounding silence after 0, 1, 2 and
15 minutes of scratching.
No big changes are detected at the following one-minute intervals until
around the twelfth minute. After that, the tendency from the second minute
spectrogram in Figure 11.22 of a stronger noise band between 2 and 6 kHz
shifts toward being a narrower noise band (approximately 1 kHz) around 5 kHz.
After 15 minutes of scratching (Figure 11.22), the appearance of a narrower
noise band is more evident. Below 2 kHz, however, not much happens to the
original audio signal and the ﬁrst two harmonics are strong.
Line spectrum plots
In the line spectrum plots in the following, only the pre- and post-scratching
state (0 respectively 15 minutes) are considered. Line spectra taken before
(Figure 11.23) and after (Figure 11.24) scratching show the same segment on
the record. The harmonic peaks have approximately the same power, but a
broad noise band is gaining strength.
The noise signal is more than 20 dB stronger after 15 minutes of scratch-
ing, which result in a masking of the harmonics above 5 kHz. From the last
spectrograms it seems that the wearing generates louder noise between 4 and
6 kHz. This noise band may be perceived as being part of the sound, especially

Chapter 11. Complex gestural audio control: the case of scratching
253
Figure 11.23: Line spectrum of the tone after 0 minutes of scratching (0-
20 kHz).
Figure 11.24: Line spectrum of the tone after 15 minutes of scratching (0-
20 kHz).
with standard scratch sounds as “ahhh”.
The silent parts
The most interesting issue is the constant level of noise that will mask the
audio signal, and the best place to look at the level and appearance of noise is
in the silent parts surrounding the audio signal. The following line spectrum
plots of silence before and after scratching illustrates to what extent the needle

254
The Sounding Object
Figure 11.25: Line spectra of the silent part before (lower plot) and after (upper
plot) scratching.
damages the vinyl record.
Silence is also affected when tearing down the grooves, in the sense that
silence is replaced by a noise signal. Figure 11.25 shows the line spectra of the
small silent gaps seen in Figure 11.22. Because the gap was short, less than
30 ms, a high bandwidth had to be chosen for the analysis. It seems that the
noise is about 40-50 dB louder after 15 minutes for frequencies below 6 kHz,
and about 20-30 dB louder for frequencies above that.
11.4.3
Discussion
As noise seem to be generated in the groove already during the ﬁrst minute
of scratching, it seems unnecessary to consider a signal to be noiseless and per-
fect, at least if the level of realism strived for is that of vinyl being manipulated.
A thing like a ‘clean’ signal will never be an issue in real scratching, which
maybe also gives scratching its characteristic sounds. This same noise that ap-
pears in real performances can be implemented in a model for scratching, and
maybe prove helpful in masking audible errors connected to resampling, which
is often a problematic concern in today’s models.

Chapter 11. Complex gestural audio control: the case of scratching
255
11.5
Design issues for a control model for scratch-
ing
Considering the analysis from experiment 2, a scratch simulator must in-
clude a volume on/off function, as almost none of the scratches are performed
with the volume constantly on. There is no need to be able to control bigger
scratch areas than 360◦, and 180◦ should be easily controlled. Probably a touch
sensitive pad could be efﬁcient for controlling the vinyl part. These are fairly
inexpensive and have advantages compared other controllers. Finding some
controller to match a real turntable will perhaps prove difﬁcult and expensive
due to the strong motor, heavy platter and the inertia.
To simulate the record playing, the sample to scratch should be looped. A
sample prepared to be altered from a standstill state does not correspond to any
real scratch situation, the closest would be a comparison with tweak-scratching,
where the motor of the turntable is turned off, but then the platter spins easily
with low friction. Many simulators today have the standstill approach. When
the sample is running in a loop, a mouse may be used for dragging the “record”
forward and backward. It will not feel much like scratching for real, however,
as you have to press the mouse button on the right place on the screen and
move the mouse simultaneously. Even if the ability to do this smoothly and
efﬁciently can be trained, there are hopefully better ways. A touch sensitive
pad is more suited to this task than both keyboards and mice. Since it registers
touch, hold-down and release, it can be programmed to act as the vinyl would
upon ﬁnger touch; a ﬁnger on the vinyl slows down the record easily to a halt
without too much pressure, and the same can be achieved with touch sensitive
pads.
From the analysis and data of the two ﬁrst experiments a model of scratch-
ing was built using pd4. The readings of the potentiometer and the crossfader
recorded in experiment 1 were used to control an audio ﬁle. By ﬁrst using the
output from the potentiometer to change the sample-rate of the audio ﬁle that
was played back, and then using the output from the crossfader circuit board
to change the playback volume level, we successfully resynthesized the few
techniques we tested on. 3 techniques involved record movement only; baby,
tear and scribble, while 2 techniques, chirps and twiddle, also involved cross-
fader movement. In the following, the measurements of these 5 techniques are
analyzed in detail and some algorithms for their simulations are proposed.
4Pure Data, or pd, is a real-time computer music software package written by Miller Puckette
(http://pure-data.org).

256
The Sounding Object
(a)
(b)
Figure 11.26: Baby scratch: rotation angle of the record during one cycle (a);
velocity of the record during one cycle (b).
11.5.1
Baby scratch model
An analysis of the data related to one baby scratch cycle (see Figure 11.26)
shows that the DJ moves the record forward and backward to its starting posi-
tion (0◦ in Figure 11.26a) in about 260 ms. The track used for the experiment
was positioned at a distance of 9 cm from the center of the record. Thus it
was possible to calculate the distance travelled by the record and the velocity
of the record itself (Figure 11.26b). The velocity of this movement has the
typical shape of target approaching tasks [74]. In the DJ pulling action, the
velocity reaches its maximum when the record has travelled a little over half of
the ﬁnal distance, then velocity decreases to 0 value when the DJ starts to push
the record forward. During the pushing action, the record increases in velocity
(see the negative values of Figure 11.26b) in a shorter time than in the pulling
phase. It thus reaches maximum velocity before having travelled through half
the distance covered in the pushing action.
11.5.2
A general look at other scratching techniques
The Same observations and measurements can be done for the other scratch-
ing techniques taken in consideration in Experiment 2. In the following only
the signals produced by the sensors are shown for each scratching type.

Chapter 11. Complex gestural audio control: the case of scratching
257
(a)
(b)
Figure 11.27: Tear scratch: displacement of the record during one cycle (a).
Scribble scratch: displacement of the record during six cycles (b).
Both chirps and twiddle scratch models use baby scratch as the basic move-
ment as do most scratches where the crossfader is the main feature. Still the
record movement varies from the simpler baby.
11.5.3
Existing scratching hardware and software
Expensive equipment and hard-to-learn playing techniques are motivations
for developers of turntable-imitating hardware and software. Several scratch
simulators have emerged during the last ten years, but none have so far proven
to be successful among the professionals. This is about to change, and one of
the promising products today is the scratchable CD players that simulate record
players by playing the CD via a buffer memory. This memory can be accessed
from a controller. In the early stages of scratch CD players this controller was
in the shape of a jog wheel, now it often is a heavy rubber platter that can freely
be revolved. Recent models have a motor that rotates the rubber platter at an
adjustable speed, making it resemble turntables even further. Buffer memory
and scratch pad controllers are used for other media formats such as MP3 and
MiniDisc as well.
The turntable itself is also used for controlling a buffer memory, either by
attaching sensors or using the signal from the record. For the latter, standard
pick-ups can be used, but the record signal must be specially coded. Attaching

258
The Sounding Object
(a)
(b)
Figure 11.28: Chirp scratch: displacement of the record during two cycles (a).
Twiddle scratch: displacement of the record during one cycle (b).
sensors to turntables has not yet been implemented in commercial products.
Software for performing scratching, often simulating turntables or mak-
ing virtual turntables, is interesting above all for its low expenses and high
versatility. The controllers are standard computer input devices or MIDI, but
customable.
The game industry develop both simple and advanced applications and ac-
companying hardware that proﬁt from the popularity of scratching. A common
ground for all of this hardware and software, from the simplest on-line Flash-
wave game to the coded vinyl records, is the turntable. The inclusion of a
crossfader-like volume manipulator should seem to be obvious, but so far it
has not been dealt with satisfyingly.
11.5.4
Reﬂections
It is not obvious to see whether models of scratching will hold a comparison
to vinyl technology. All simulators have in common their digital approach,
which is quite natural, but there are beneﬁts and catches with vinyl that are
either overlooked or even sidestepped. One speciﬁc example of a vinyl-typical
feature is the deterioration of the vinyl; a few minutes of dragging the needle
continually over the same spot on the record has devastating consequences for
the sound quality, and quoting experiences of DJs, the needle even responds

Chapter 11. Complex gestural audio control: the case of scratching
259
differently to movement over that spot. CD players will not wear out grooves
the same way a record player does, and this might take the edge off a sound the
same way a producer in a recording studio can polish a rough performance to
the nearly unbearable.
To simulate every aspect of the turntable, the vinyl, the needle and the more
remote aspects like wearing, will probably turn out to be the only suitable op-
tion for making an acceptable replacement for today’s instrument set-up. An
approach built on physics-based modelling technique seems therefore appro-
priate and worth to experiment with in the future [206].
Arguably, the most characteristic quality in scratching is the big range of
recognizable and universally agreed-upon playing techniques. Future research
can reveal interesting issues regarding these. Also, technology aiming to re-
place the turntable should take into consideration the role and practises of
scratch techniques. The techniques and characteristics of the hand movements
associated with different types of scratches will be examined in future invest-
igations.
11.A
Appendix
The measurements conducted in the experiments reported in chapter 11
were used for the design of a model of scratching. The environment for this
model is pd5. Sound models of friction sounds can be controlled by the
scratch software, but it can also control recorded sounds in the same manner as
turntables. The pd patch is open and customizable to be controlled by various
types of input devices. We have tested the patch with both recorded sounds
and physically modelled friction sounds, and we have controlled the model by
use of computer mice, keyboards, MIDI devices, the Radio Baton, and various
sensors connected to a Pico AD converter6.
5Pure Data http://pure-data.org.
6Pico
Technology.
The
ADC-11/10
multi
channel
data
acquisition
unit,
http://www.picotech.com/data-acquisition.html.

260
The Sounding Object
11.A.1
Skipproof - a pd patch
Skipproof7 has three main functions. It is an interface for manipulating
the playback tempo of a sound-ﬁle by using a computer input device, and it is
an interface for triggering models of single scratching techniques. With these
two functionalities, Skipproof acts as both a virtual turntable and a scratch
sampler/synthesizer. In addition, the output volume can be controlled manually
or by the models of scratching as a signiﬁcant part of some of the techniques.
With this third functionality, Skipproof also simulates the scratch audio mixer.
Method
In addition to pd, Skipproof uses a GUI front-end program written for pd,
called GrIPD8. pd processes all sounds, and GrIPD controls the different
options made possible in pd.
Material
The sounds manipulated in Skipproof are 16 bit 44.1 kHz and 88.2 kHz
mono wave-ﬁles, but other formats should easily be supported. Sounds, or
‘samples’ in analogy to DJ-terms, are meant to be 1.6 s long in order to imitate
a real skip-proof record, yet there is no restriction to the length.
Apart from direct manual “scratch control” of a sound-ﬁle, it can be ac-
cessed via recorded scratch movements. These recordings originate from the
measurements reported in the presented experiments.
Control concepts
Skipproof can be controlled by different sensors and hardware, and is easy
to adjust to new input objects. Sensors, MIDI input and computer inputs (key-
board and mouse) are used both to trigger the scratch models and manipulate
the virtual turntable and audio mixer.
7The name Skipproof is taken from a feature found on DJ-tools records called a skip-proof
section, where a sound (or set of sounds) are exactly one rotation long and repeated for a couple of
minutes. If the needle should happen to jump during a performance, chances are quite good that it
will land on the same spot on the sound, but in a different groove. The audience must be very alert
to register this jump.
8GrIPD, or Graphical Interface for Pure Data, is written by Joseph A. Sarlo
(http://crca.ucsd.edu/~jsarlo/gripd/).

Chapter 11. Complex gestural audio control: the case of scratching
261
Figure 11.29: Graphical interface for Pure Data, GrIPD with turntable and
audio mixer controls.
Implementation
In the following, selected screenshots from the pd patch will be commen-
ted, explaining brieﬂy how Skipproof is designed. pd allows the user to build
complex patches with sub-patches and references to other patches. Skipproof
is built up by many subpatches that send and receive control signals from and
to one another.

262
The Sounding Object
GrIPD
Figure 11.29 shows the performance window in Skipproof. One main focus
designing the graphical interface was to some extent copy a turntable and a
mixer. There are also a number of other buttons and sliders not found on the
standard hardware, enabling the DJ to change parameters of, amongst others,
motor strength. The user will not have to open any other window than this
interface just to play.
Turntable and mixer
The large light grey rectangle in Figure 11.29 is the part that registers
mouse action (when left mouse button is held down). The meter next to the
grey area displays sound progression marked with each quarter round (90◦,
180◦, 270◦ and 360◦ ). Around this ‘vinyl record part’ all the standard turntable
buttons are collected; start/stop, two buttons for toggling 33 and 45 rpm, and
a pitch adjustment slider. On a turntable there is also a power switch that lets
the platter gradually stop rotating by its own low friction. When stopping the
turntable with the stop-button it is the motor that forcefully breaks the rota-
tion speed. The power-switch is sometimes used to produce a slow stop, but is
omitted as a controller here.
Only two controllers are chosen from the audio mixer’s many possibilities.
The up-fader is a logarithmic master-volume slider. Normally the crossfader
is far more utilized than the up-fader, but a slider is not an advantageous way
to control volume when the mouse is occupied with record speed. Under the
slider is a push-button which shuts out the sound (or turns on the sound) when
activated. This button mixes the functions of the line/phono switch and the
crossfader.
Other controllers
Top left in Figure 11.29, there is a main power-button “power up dsp” start-
ing the audio computation and resetting or initializing some start values in the
patch. Under this there are 5 buttons for selecting the playback sound (sample).
Under the heading “readymade scratches” there are several buttons for trig-
gering the recorded techniques. Below, two sliders deﬁne the speed and the
depth these techniques will have. The speed range is a bit broader than what is
normally performed. The depth slider goes from long backward movements to
long forward movements, also making exaggerated performances possible.

Chapter 11. Complex gestural audio control: the case of scratching
263
Figure 11.30: Main patch for Skipproof.
The button labelled “using volume switch” decides whether the recorded
scratches should be performed with crossfader or an on-off switch.
The pd patches
The main window, Figure 11.30, opens the GUI and lists all the subpatches.
The right side of the window receives the playback speed of the sound in rounds
per second (rps). This information is sent to the progression meter in GrIPD.
The pd trackselection subpatch lets the user choose sounds and
sample rates. All sounds will be read into the same table, “sample-table a”,
to reduce the CPU load.
“Metro” in pd is a metronome object counting at a deﬁned speed. Here
in pd mousesens the metro counts every 100 ms, and at every count re-
gisters changes in relative mouse position. Too slow or too fast movements
(often caused by long time of no action or by inaccuracy in the mouse sensors)
are ﬁltered out. Both horizontal and vertical mouse activity is measured. The

264
The Sounding Object
Figure 11.31: Mousesens: Calculating the mouse movement.
mouse speed value is sent to subpatch pd loopspeed for adjusting the play-
back sample rate.
The pd loopspeed is sent to the table-reader as seconds per round and
can be altered by receiving the mouse speed, the pitch control value and on-
and-off messages. When the motor is turned off, the turntable will respond
differently to movement caused by mouse activity. Some kind of inertia can be
simulated, as in “Return to loop speed” in the top right corner of the window
in Figure 11.32.
All the recorded scratches used for synthesizing single techniques are col-

Chapter 11. Complex gestural audio control: the case of scratching
265
Figure 11.32: The loopspeed subpatch.
lected in pd tables for simplicity. Tables are read in pd scratch-o-ma-
tics. The empty “table11” is for techniques where the crossfader is not util-
ized, in this way all techniques can follow the same procedure in the subpatch
described next.
Signals from crossfader and record movements are low-pass ﬁltered at 30-
50 Hz before implemented in Skipproof. Each of the techniques is picked
out from a series of constantly performed single techniques, and so represent
an idealized model. Apart from techniques where the main idea consists of
many small movements on the record, as with chirps and scribble, only one
stroke forward and backward is included for all scratches. The scratches vary
in length.
In future versions, most of the tables will be substituted by algorithms for

266
The Sounding Object
Figure 11.33: pd tables: The recordings of the techniques in tables.
both record and crossfader movement.
The subpatch in Figure 11.34 reads the tables in pd tables using the
same procedure, but since the tables are of different sizes, some adjustments
must be done to the computations. The record-movement table readings are
sent to the main patch and replace the value from pd loopspeed in seconds
per round. The crossfader-movement table readings are sent to pd volcon-
trol as both up-fader values and volume push-button values depending on
which method is selected.
After a performed scratch, the turntable continues in the set rpm.

Chapter 11. Complex gestural audio control: the case of scratching
267
Figure 11.34: Scratch-o-matics: Reading the recorded techniques.
Noise and wearing
To simulate the wearing of the vinyl, as explained in experiment 3, a simple
noise model was implemented, see Figure 11.35. Following several notions, it
generates low-level white noise, narrow-band noise and vinyl defects as cracks
and hiss. All the noise signals are recorded to a 1.6 s long table, so the vinyl
defects always occur at the same spot on the record when it is looped.
11.A.2
Controllers
Here are some alternatives to standard MIDI and computer input controllers
that we use. The model is controlled in 4 different areas. An analogue-digital
converter from Pico sends the signals from the control objects to the computer.
The voltage output is then read in pd, controlling the described parameters.

268
The Sounding Object
Figure 11.35: Noise generator.
Substituting the turntable
The Max Mathews’ Radio Baton was used as gestural controller for Skip-
proof. The drumstick like batons were substituted by a newly developed radio
sender that ﬁts the ﬁngertips. This new radio sender allows users’ interaction
based on hand gestures (see Figure 11.36).
Substituting the mixer
The crossfader on modern scratch mixers is becoming easier and easier to
move; now some models have friction-free faders. Still it takes a lot of training
to accurately jump the fader over the critical break-in point. To make it easier
to accomplish fast clicks, a light sensor replaces the crossfader.
Substituting the record
Sounds in Skipproof are sampled sounds. The user can add her/his own
choice of sounds to be scratched. Skipproof can also be applied to the control

Chapter 11. Complex gestural audio control: the case of scratching
269
Figure 11.36: The ﬁnger-based gestural controller for the Max Mathews’ Radio
Baton.
of the sound model, such as for friction.
Substituting the DJ
Max Mathews Radio-baton is divided into nine sectors, each sector hosting
a pre-recorded scratch technique. Treated gloves (with wiring equivalent to
the drumstick used with the Radio-baton) manipulate a 3D (xyz-plane) signal
received by the antennas.

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Document Outline

Preface
Foreword
Everyday listening: an annotated bibliography
- 1979
- 1984
- 1987
- 1988
- 1990
- 1991
- 1993
- 1997
- 1998
- 2000
Prolegomena to the perceptual study of sounds
- The perceptual study of sounds
- Perception and psychophysics
- Geographical and behavioural environment
- Hearing the source
- On recognition
- On physical models
- On the ecological approach
- On phenomenology of sounds
- On expressive sounds
- Some findings and suggestions
Sound objects and human-computer interaction design
- Background
- How to design more usable auditory interfaces?
- The novelty of sound objects in interaction design
- A roadmap to interaction design with sound objects
- Implementation issues
- Summary
- Acknowledgments
Impact sounds
- Introduction
- Analysis of the physical event
- Overview of the researches
- The effect of sounds' manipulation
- Scaling with real sounds
- Interaction between height, distance and mass
- General discussion
Material categorization and hardness scaling in real and synthetic impact sounds
- Introduction
- Material
- Hardness
- Overall discussion
Size, shape, and material properties of sound models
- Spatial features
- Material
Experiments on gestures: walking, running, and hitting
- Introduction
- Control models
- Walking and running
- Modeling gestures of percussionists: the preparation of a stroke
- Auditory feedback vs. tactile feedback in drumming
Low-level models: resonators, interactions, surface textures
- Introduction
- Modal resonators
- Interactions
- Implementation and control
- Appendix -- Numerical issues
High-level models: bouncing, breaking, rolling, crumpling, pouring
- Sound design around a real-time impact model --- common basics
- Bouncing
- Breaking
- Rolling
- Crumpling
- Some audio cartoons of fluid movements
Synthesis of distance cues: modeling and validation
- Introduction
- Acoustics inside a tube
- Modeling the listening environment
- Model performance
- Psychophysical validation
- Conclusion
Complex gestural audio control: the case of scratching
- Introduction
- Experiment 1 - The techniques of scratching
- Experiment 2 - Analysis of a genuine performance
- Experiment 3 - Wearing of the vinyl
- Design issues for a control model for scratching
- Appendix
Devices for manipulation and control of sounding objects: the Vodhran and the InvisiBall
- Introduction
- The virtual Bodhran: the Vodhran
- The InvisiBall: Multimodal perception of model-based rolling
- Acknowledgments
- Appendix -- Modal synthesis
Psychoacoustic validation and cataloguing of sonic objects: 2Dbrowsing
- Introduction
- The Sonic Browser
- The Sonic Browser - An overview of its functionality
- Experiments in the validation scenario using the Sonic Browser
- Cataloguing experiment using the Sonic Browser
- Conclusions
Software tools for Sounding Objects
- Introduction
- Rapid prototyping tools
- Self-contained, stand-alone applications
GNU Free Documentation License
Index
References