[PD] Documentation
Joseph Zitt
jzitt at josephzitt.com
Wed Jun 19 19:13:25 CEST 2002
For what it's worth: I've written up the following documentation of the
PD patches that I used on tour this past winter, to be submitted as a
writing sample for a job application. (Anybody wanna hire a technical
writer?) It might serve as a model for offline ASCII-based documentation
for PD. (The patches themselves are a mess, with lots of unused objects,
test connections, and other problems, so I suspect it's not worth
releasing the patches themselves in their current state.)
<SAMPLE>
Name Purpose
improvoice Processes an audio input by shifting its pitch and adding
delays as specified by live interaction.
Description
The improvoice patch was developed to process live vocal
improvisation, with an eye toward ease of use and flexibility
as well as minimizing the amount of computer processing
needed. All interaction is done via a mouse. (In the initial
performances, a handheld pointer device was used instead of a
mouse, leaving the performer free to gesture without needing
contact with a keyboard.)
The audio signal, passed into the computer via an A/D
converter, first flows through the shift-multiply patch, which
shifts the pitch of the signal by a just-intoned interval as
set by the shiftdirection and shiftamount controls. A blender
patch then mixes the pitch-shifted signal and the original
unshifted signal, with the proportions set by the shiftmix
control. The mixed signal then flows into the delayer patch
containing four separate delays of differing lengths, with its
input volume set by an inputcontrol control and the amount of
delayed signal fed back into the delays set by the loopcontrol
control. Another blender patch mixes the output of the
delayer patch with the undelayed signal, with the proportions
set by the delaymix control. The mixed signal is then fed
through a high-pass filter set to a very low frequency (which
cleans some system noise from the sound) then out through the
D/A converter, with the output level determined by the
fadecontrol control.
Inlets
Order Type Description
1 adc~ Audio signal from A/D converter
Outlets
Order Type Description
1 dac~ Signal sent to D/A converter
User interface controls
Name Description
shiftdirection Direction of pitch shift
Controls
Type Value Result
Message 1 Pitches are shifted upward.
Message -1 Pitches are shifted downward.
Name Description
shiftamount Amount of pitch shift, by just-intoned
intervals. If the shiftdirection control is
set to "1", pitches are shifted upward by the
intervals shown for each message control. If
the shiftdirection control is set to "-1",
pitches are shifted to an octave below the
pitch to which they are when it is set to "1",
with two exceptions: if the shiftamount
control is set to "0", the pitch is not
shifted in either direction; if the
shiftamount control is set to "1", the pitch
is shifted up by one octave if the
shiftdirection control is set to "1" and down
by one octave if the shiftdirection control is
set to "-1".
Controls
Type Value Result
Message 0 No shift
Message 1 2/1 Octave
Message 2 3/2 Perfect fifth
Message 3 4/3 Perfect fourth
Message 4 5/4 Major third
Message 5 6/5 Minor third
Message 6 7/6 Septimal minor third
Message 7 8/7 Septimal whole tone
Message 8 9/8 Major whole tone
Message 9 10/9 Minor whole tone
Message 10 11/10 (unnamed)
Message 11 12/11 Median second
Message 12 13/12 (unnamed)
Name Description
shiftmix Determines the blend between the
pitch-shifted and unshifted signals.
Controls
Type Value Result
Message 0 Unshifted signal only
Message 0 1000 Change to unshifted signal only
over one second
Message 50 Even balance of pitch-shifted
and unshifted signal
Message 50 1000 Change to even balance between
pitch-shifted and unshifted
signal over one second
Message 100 1000 Change to pitch-shifted signal
only over one second
Message 100 Pitch shifted signal only
Number 0-100 Slides between integer values
from unshifted signal only (0)
to pitch-shifted signal only
(100)
Name Description
inputcontrol Determines the volume of signal fed into
the delayer patch
Controls
Type Value Result
Message 0 No signal
Message 0 1000 Fade out input over one second
Message 100 1000 Fade up to full volume over
one second
Message 100 Full volume
Number 0-100 Slides between integer values
from no signal to full volume
Name Description
loopcontrol Determines the percentage of feedback in the
delayer patch
Controls
Type Value Result
Message 0 No delay
Message 0 1000 Change to no delay over
one second
Message 99 1000 Change to maximum delay feedback
over one second
Message 99 Maximum delay feedback
Number 0-99 Slides between integer values
from no delay to maximum
Name Description
delaymix Determines the blend between the original
and delayed signals
Controls
Type Value Result
Message 0 Original signal only
Message 0 1000 Change to original signal only
over one second
Message 50 Even balance of delayed and
original signal
Message 50 1000 Change to even balance between
delayed and original signal
over one second
Message 100 1000 Change to delayed signal
only over one second
Message 100 Delayed signal only
Number 0 100 Slides between integer values
from original signal only (0)
to delayed signal only (100)
Name Description
fadecontrol Determines the output volume
Controls
Type Value Result
Message 0 Silence
Message 0 1000 Fade down to silence over
one second
Message 99 1000 Fade up to full volume over
one second
Message 99 Full volume
Number 0-99 Slides betwen integer values
from silence to full volume
Other patches called
blender
delayer
shift-multiply
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Name Purpose
blender Mixes two audio signals.
Description
A numeric control inlet determines the balance between the
signals. For example, when the control value is set to "75"
the blender patch attenuates the first signal to 75% of its
incoming strength and attenuates the second signal to 25% of
its incoming strength, returning the mixed signal at the
signal outlet.
Inlets
Order Type Description
1 Signal First audio signal
2 Signal Second audio signal
3 Control Number 0-100 Controls the mix of the first and
second signal. The number
indicates the percentage of the
first signal in the mixed output.
The percentage of the second
signal is 100 minus the control
value.
Outlets
Order Type Description
1 Signal Mixed audio signal
User interface controls
None
Other patches called
None
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Name Purpose
delayer Sends audio signal through a series of looping delays
Description
This patch uses a set of four delays, with delay times of
1000, 1010, 1015, and 1025 milliseconds. Each delay sends its
output to the patch's signal output and feeds its output back
into itself, attenuated to the percentage of its output value
determined by the control inlet. For example, a control value
of "75" causes the output of each delay to be fed into itself
at 75% of its output strength each times.
The control value affects the number of repeats exponentially:
For example, when the control value is set to "50", the signal
is attenuated to 50% of its original strength when first fed
back in, 25% the second time, 12.5% the third time, and thus
disappears rather quickly. When the control value is set to
"99", the signal is fed back in at 99% the first time, 98.01%
the second time, 97.03% the third time, and fades away much
more slowly.
You can clear the delays instantly by setting the control
value to "0", or clear it quickly but more gradually by
setting it to a value below "20".
Due to the very close but varied delay times, input signals
with gradual envelopes tend to smooth out into steady washes
of sound. Sharp attacks or decays result in phasing rhythmic
patterns, reminiscent of the early music of Steve Reich.
Inlets
Order Type Description
1 Signal Incoming audio signal
2 Control Number (Range: 0-99)
Percentage of signal fed into delay on each
repeat
Outlets
Order Type Description
1 Signal Outgoing audio signal
User interface controls
None
Other patches used
None
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Name Purpose
shift-multiply Shifts the pitch of a signal by an indicated ratio
Description
This patch, derived from the "56.delay.pitchshift.pd" pitch
shifter supplied with the PD documentation, shifts the
frequency of an incoming signal according to a control value.
If the control value is positive, the patch shifts the
frequency by the ratio of n/(n-1) where n is the control
value. For example, a control value of "3" shifts the
frequency by a ratio of 3/2 (a just-intoned perfect fifth
above the frequency of the incoming signal).
If the control value is negative, the patch shifts the
frequency by the ratio of n/n+1 where n is the absolute value
of the control value. For example, a control value of "-3"
shifts the frequency by 3/4 (a just-intoned perfect fourth
below the frequency of the incoming signal).
If the control value is zero, the incoming signal is passed
through unaltered.
While the patch can accept non-integer control values, integer
values provide simpler and clearer pitch relationships.
Inlets
Order Type Description
1 Signal Incoming audio signal
2 Control Determines ratio of pitch shifting
Outlets
Order Type Description
1 Signal Outgoing pitch shifted audio
User interface controls
None
Other patches used
None
</SAMPLE>
--
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