[PD] Pd-list Digest, Vol 79, Issue 74

[Samuel Burt]

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 at gmail.com>
> Subject: Re: [PD] Analyzing subharmonic frequencies accurately
> To: pd-list at iem.at
> Message-ID:
> 	<CAFY0eaozjc=xMoq3h2mJo6XmAhtKz-V1+XfM44ps4s+ZMb=12A at 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 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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> 
> 

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