As a preamble, I'll note that I posted a question on chuck-dev about AutoCorr/XCorr always crashing for me. This patch <https://github.com/ccrma/chuck/pull/150> seems to fix that.
That said, I don't understand the results I get from AutoCorr. For periodic inputs, I expect to see periodicity in the output. For small FFT sample sizes, I see the expected peak at 0, and at large sample sizes I see a second peak at the end of the window. See example plots at 128 <https://i.ibb.co/BBZXgBB/autocorr-128.png> and 4096 <https://i.ibb.co/Mn5fty5/autocorr-4096.png>. That second peak is correlated with the window size, not the input frequency. Thanks to Mario for his gnuplot wrapper <https://github.com/mariobuoninfante/ChucK_various> that captured those plots. Here's the plotting code if anyone would like to repro: SinOsc s => FFT fft =^ AutoCorr c => blackhole; 4400 => s.freq; 128 => fft.size; 300::ms => now; c.upchuck(); Plot plot; "autocorrelation of 4400 hz, 128 samples" => plot.title; plot.plot(c.fvals()); 200::ms => now; Should I be using AutoCorr differently? Am I looking at the power spectrum or something, and not the correlation vector like I think I am? My current understanding comes from reading uana_extract.cpp many times with references like this <http://paulbourke.net/miscellaneous/correlate/>. Thanks, Curtis
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