puredata-doc 0.47.1-3 / usr / share / puredata / doc / 3.audio.examples / E01.spectrum.pd

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#X text 134 243 <-- click to graph;
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#X obj 85 248 tabwrite~ E01-spectrum;
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#X text 83 93 Fourier series;
#X text 88 146 magnitude;
#X text 86 131 calculate;
#X text 21 3 This subpatch computes the spectrum of the incoming signal
with a (rectangular windowed) FFT. FFTs aren't properly introduced
until much later.;
#X text 83 62 signal to analyze;
#X text 182 166 delay two samples;
#X text 181 182 for better graphing;
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#X text 146 540 <-just out of curiosity \, here's the pitch;
#X text 14 319 At load time \, calculate a good choice of fundamental
frequency for showing spectra: the 16th bin in a 4096-point spectrum
\, so SR*16/4096 or SR/256.;
#X text 135 216 "bang" into this inlet to graph it;
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#X text 531 173 ---- 0.02 seconds ----;
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#X text 523 800 updated for Pd version 0.37;
#X text 516 359 1;
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#X text 520 378 -- partial number --;
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#X text 303 136 <-- On/Off;
#X text 337 152 for each;
#X text 339 168 partial;
#X text 595 11 WAVEFORM;
#X text 578 204 SPECTRUM;
#X text 25 415 The next series of patches demonstrates various kinds
of modulation: AM \, waveshaping \, and FM. We will need a tool for
graphing spectra which is introduced here. In this patch the signal
to be analyzed is a simple sum of up to six partials of a fundamental
frequency (which is 172 Hz \, close to F below middle C \, if your
sample rate happens to be 44100 Hz. The fundamental is chosen to agree
with the analysis patch ("pd FFT") and is computed within it).;
#X text 25 546 The partials are numbered 0 through 5 \, where 0 means
DC \, or zero frequency \, 1 is the fundamental \, and so on. The toggle
switches allow you to turn them on and off separately. You have to
press the "click to graph" button to update the two graphs.;
#X text 745 344 0;
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#X text 744 282 0.5;
#X text 26 631 The upper graph is just the (time domain) waveform \,
about four periods long. The lower graph is the magnitude spectrum.
Its peaks are the magnitudes of the partials. Note that a DC signal
of amplitude one is considered a partial of magnitude 1 \, but the
other partials \, which have peak amplitudes of 1 (and RMS 0.707) \,
have peak magnitudes of only 0.5 in the spectrum.;
#X obj 41 222 *~ 1;
#X text 733 37 5;
#X text 734 157 -5;
#X text 81 221 sum;
#X text 96 5 GRAPHING SPECTRA OF AUDIO SIGNALS;
#X text 24 742 Here we're introducing a new feature: multiple signals
connected to a signal inlet (as in the "*~ 1") are added. This is the
most convenient way to sum the six partials.;
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