Katja, that sounds like a nice approach. With sound file playback, I could just delwrite~ the audio 3 seconds so everything would resync. I'm going to have to go back and look at fft, again. I spent a lot of time figuring out how to use [fft~] a few years ago. I'm not quite clear on how to tell what Hz value each bin is indicating. Wait, is it as simple as sample-rate/block-size=Hz?

By the way, if I was starting at the beginning with [fft~] this is the place I would go to start figuring it out:
http://www.pd-tutorial.com/english/ch03s08.html
Many thanks to Johannes Kreidler for these excellent and thorough guides. It's an excellent place to discover new things, even for experienced users.

Sam






------------------------------

Message: 7
Date: Mon, 17 Oct 2011 23:43:45 +0200
From: katja <katjavetter@gmail.com>
Subject: Re: [PD] Analyzing subharmonic frequencies accurately
To: pd-list@iem.at
Message-ID:
<CAFY0eaozjc=xMoq3h2mJo6XmAhtKz-V1+XfM44ps4s+ZMb=12A@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Hi,

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
then.

Katja



On Mon, Oct 17, 2011 at 11:24 PM, Samuel Burt
<composer.samuel.burt@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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