[PD] sampling animation example

[Orm Finnendahl]

Hi all,

I attached an animation of the basics of sampling and synthesizing
made for my csound class here in Berlin using pd and its graphic
capabilities. It had quite some effect on my students (they normally
use Max/MSP) and definetely changed their attitude towards pd ;-)

It only covers the most basic principles of sampling and synthesizing
in the digital realm but IMO explains things much clearer and easier
to understand than lengthy written explanations. It might look strange
as I'm using a 6x10 console font and didn't check it against the
standard pd font.

This also could be considered my first contribution to Krzysztof's pd
doc project (although it doesn't document pd itself and might be off
topic due to its more general nature).

--
Orm
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#X text 72 358 output table;
#X text 71 157 red - input signal;
#X text 70 169 green - sampled values from input signal;
#X text 503 81 show x - increments;
#X text 348 13 input signal;
#X text 455 13 sampler;
#X text 349 212 freq;
#X text 503 113 capture to output table;
#X text 503 132 clear output table;
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#X text 660 209 amplitude;
#X text 456 213 samplerate;
#X text 392 350 oscil;
#X text 459 350 xamp \,;
#X text 509 350 xcps \,;
#X text 331 350 aout;
#X text 330 311 csound orc-statement;
#X text 563 350 f-table-no;
#X text 392 332 oscil;
#X text 562 332 1;
#X text 350 258 scale input freq;
#X text 350 270 slider to show aliasing;
#X text 752 357 Orm Finnendahl 2002;
#N canvas 533 2 450 573 help1 0;
#X text 10 22 This patch exemplifies two basic principles of digital
;
#X text 10 34 signal processing: sampling audio and synthesizing wave
;
#X text 10 46 forms. It was written for a csound class in Berlin 2002.
;
#X text 10 58 below is a description of sampling. click on "pd help2"
;
#X text 10 70 for help on synthesizing wave forms.;
#X text 10 94 1. sampling audio;
#X text 10 118 click the toggle below "input signal" to show an animated
;
#X text 10 130 simulation of a sine wave oscillation of some signal
;
#X text 10 142 (represented by the red square) \, say \, received at
the inlet;
#X text 10 154 of a digital-to-analog converter. In order to sample
the;
#X text 10 166 signal \, the value of the input signal is measured
at;
#X text 10 178 regular time intervals \, called the "sampling rate"
(or sr).;
#X text 10 190 click on the toggle below "sampler" to show this in
;
#X text 10 202 animation. If the frequency of the input signals change
\,;
#X text 10 214 (left slider) \, the number of samples per period gets
lower \,;
#X text 10 226 if the sr isn't changed (which is the normal case in
;
#X text 10 238 digital audio). To see \, how the sampled values get
stored;
#X text 10 250 (in a soundfile for example) \, move the slider of the
;
#X text 10 262 sampler all the way up and click on the "capture to
output;
#X text 10 274 table" toggle. Watch how the frequency of the wave stored
;
#X text 10 286 in the output table changes if you move the left (input
;
#X text 10 298 signal) slider.;
#X text 10 334 aliasing;
#X text 10 358 click on the toggle below the input signal slider to
set;
#X text 10 370 the frequencies of the input signal and the sample rate
to;
#X text 10 382 the same value (5 Hz). Watch how the sample stays on
the;
#X text 10 394 same value all the time and the captured signal becomes
a;
#X text 10 406 horizontal line (if the green square is barely visible
\,;
#X text 10 418 stop the sampler and try to start it in a moment when
the;
#X text 10 430 red square is near the left edge of the f-table window).
;
#X text 10 442 If you increase the frequency of the input signal \,
the;
#X text 10 454 green square starts moving to the right \, if you decrease
it;
#X text 10 466 beyond 5 Hz \, it starts moving to the left. Notice
that the;
#X text 10 478 frequency of the sampled signal is equal for input;
#X text 10 490 frequencies symmetrical to 5 Hz (e.g. 5.141 Hz and 4.859
;
#X text 10 502 Hz). Since the green square seems to move in the opposite
;
#X text 10 514 directions \, the sampled signals below 5 Hz are 180
degree;
#X text 10 526 phase shifted versions of the signals above 5 Hz.;
#X restore 72 308 pd help1;
#N canvas 0 0 450 300 help2 0;
#X text 16 24 now go back to the previous example once again: turn
off;
#X text 16 36 the "scale input freq" toggle \, turn off "capture to
output;
#X text 16 48 table" and move the sliders for the input frequency and
;
#X text 16 60 sample rate all the way down (to 0.1 and 10 Hz;
#X text 16 72 respectively).;
#X text 16 96 2. synthesizing wave forms;
#X text 16 120 if we are going to synthesize wave forms \, we simulate
the;
#X text 16 132 previous example within the computer. If you turn on
the;
#X text 16 144 input signal \, the sampler and the "show x-increments"
;
#X text 16 156 toggle \, you can see the regular horizontal spacing
of lines;
#X text 16 168 during the sampling process. If you increase the input
;
#X text 16 180 frquency \, watch how the spacing also increases. This
gives;
#X text 16 192 a method to generate output signals of different;
#X text 16 204 frequencies using a constant sampling rate: read cyclically
;
#X text 16 216 through a stored function table of one period of the
;
#X text 16 228 waveform you want to generate. The x-increment gives
a;
#X text 16 240 measure of the obtained frequency. You can generate
any;
#X text 16 252 periodic waveform that way. To check that out \, draw
in the;
#X text 16 264 f-table window (start by clicking on any point in the
curve;
#X text 16 276 and drag the mouse).;
#X text 16 300 The window "csound orc-statement";
#X text 16 312 shows the moving values of the variables during the
;
#X text 16 324 generation of output. In addition you can change the
;
#X text 16 336 amplitude with the right slider.;
#X restore 72 329 pd help2;
#X text 131 308 click here for instructions;
#X text 111 216 restore f-table to sine-wave;
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