[PD] Analyzing subharmonic frequencies accurately

katja katjavetter at gmail.com
Mon Oct 17 23:43:45 CEST 2011


With fft~ you can go up to a framesize of 2^17, that is around 3
seconds when assuming 44.1KHz SR. The bin resolution is then ~0.37 Hz
which may be just accurate enough for your purpose (spectral leakage
will always make analysis less precise than the bin resolution
suggests). Notice that the latency of your info will also be 3 seconds


On Mon, Oct 17, 2011 at 11:24 PM, Samuel Burt
<composer.samuel.burt at gmail.com> wrote:
> A friend of mine asked me if I could make some kind of filter that could provide information about subharmonic frequencies. I wasn't quite sure what he meant, but I thought I'd try a few things to see what I could get.
> He mentioned he wanted the following bands 1-3 Hz, 4-6 Hz, 7-9 Hz, 11-14 Hz, and 15-18 Hz.
> The first thing I tried was a series of [lop~] and [hip~] filters in the ranges he was wanting. I stacked multiple [lop~]s and [hip~]s, to make really hard limits and then sent the output from each band to vu~ meters. This was unreliable. In fact, a 5 Hz sine wave seemed more likely to show up in the 10 Hz band. I also tried [bp~], [vcf~], and [svf~] with no luck.
> I then took a different approach, using [threshhold~] and [timer] to time the distance between zero crossings and output the result. This is very reliable for a sine wave, but I fear it wouldn't be that useful for real world signals.
> Have any of you ever tried to separate out subharmonic frequencies in Pd? Any experience with brain wave analysis in software? What's a better technique?
> Thanks,
> Sam in Baltimore
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