On Jul 31, 2006, at 6:43 AM, Jamie Bullock wrote:
There is an cross-correlation class [cc~] in the flib library,
which you can use to do auto-correlation. It has both a time domain
and a frequency domain CC function. I found the output of the time
domain implementation to be easier to interpret.
I've forgotten all my DSP math, could you enlighten me as to how I
might use this?
There are also number of other feature extraction objects in flib
that might help with what you need, including [peak~], which does
the same as [peakit~] except that with [peak~] the magnitude
spectrum isn't calculated by the object, so you can precalculate
the power spectrum, log mag spectrum, cepstrum and pass it to the
object. With [peak~] you can also set a threshold as a percentage
below the maximum peak found.
I checked out [peak~], it looks like its outputting data similar to
what I am looking for, but in a strange format. How can I get just
the frequency of the highest peak? Also, I would like to have much
higher resolution. Is that possible?
You might find [bmax~] useful, as it returns the bin numbers of the
n most prominent partials, I think similar to ekext/[hasc~]. (ekext/ [hssc~] might also be useful, but you have probably already tried).
I played a bit, and didn't really get anywhere. More on that later...
Also you might want to try flib/[irreg~], flib/[ss~] which measure
spectral irregularity and spectral smoothness respectively.
I will play with those in the future, for sure.
.hc
I guess it depends how prominent you are expecting the feedback to
be, and how it is distributed across the spectrum.Let me know how you resolve this issue, as I am very interested in
this.HTH,
Jamie
BTW: sounds like a good installation!
On Mon, 31 Jul 2006 01:01:56 -0400 hans@eds.org wrote:
This isn't a standard feedback suppression system that I am after. I want to be able to play with the feedback while having the ability to prevent it from taking over. Its part of an interactive installation I am working on, the next generation of this:
The autocorrelation stuff sounds interesting, plus I just found Ed Kelly's [peakit~], which gives amplitude info of FFT channels.
.hc
On Jul 31, 2006, at 10:23 AM, padawan12 wrote:
Feeback tends toward periodicity at 1/t for a delay of t so you could do an autocorrelation (expensive - does Pd have an object to help with that?) of te feedback signal to look for it. Since you know the frequency in advance a simple bp filter is more effective. Not sure what you mean by "dominant" part. If gain is greater than unity then it will eventually be, but if you think of a Karplus=Strong it is by definition once the excitory signal has vanished. Am I understanding your question(?) if I say the best way is to simply monitor the amplitude , because if G>1 the amplitude will *always* keep growing.
On Sun, 30 Jul 2006 19:07:12 -0400 Hans-Christoph Steiner hans@eds.org wrote:
Has anyone done anything with trying to detect feedback in a
signal? I am not looking so much for feedback suppression techniques, but rather detection techniques. I am working on a system that has a slow feedback loop. I want to detect when feedback is the dominant part of the signal, and make the system respond in novel ways..hc
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