/usr/share/puredata/doc/3.audio.examples/H08.heterodyning.pd is in puredata-doc 0.47.1-3.
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#X text 336 665 updated for Pd version 0.39;
#X text 109 12 MORE ON MEASURING SPECTRA: HETERODYNING;
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#X text 56 248 signal to;
#X text 58 268 analyze;
#X text 51 44 Another method for picking out the strengths of partials
in a sound is heterodyning. We guess the frequency of a partial (as
in the previous patch) but this time we multiply by a complex exponential
to frequency-shift the partial down to zero (DC).;
#X text 47 126 Then a low-pass filter (applied separately on the real
and imaginary parts) removes all but the DC component thus obtained.
The result is two audio signals (which we take snapshots of) holding
the real and imaginary parts of the complex amplitude of the partial
we want. Compared to the previous method \, this had the advantage
of reporting the phase of the partial as well as its frequency.;
#X text 240 358 modulate;
#X text 237 394 to DC;
#X text 154 321 <-- test frequency;
#X text 236 376 test frequency;
#X text 132 471 low-pass filter;
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