# [PD] resonant comb filter series

derek holzer derek at x-i.net
Tue Feb 15 17:48:22 CET 2005

```Hi Pun Chik,

> hi . can u send me an example patch of this harmonic series of resonant
> comb filters...im really interested in learning this. an example patch
> would be really nice

I'm a bit too busy to make a simple demo right now, but the principle is
easy to understand:

A comb filter is simply a very short delay with a high amount of
feedback. It is so short that it's length becomes an oscillating
waveform. Try making a simple [delwrite~ delayname] and a [vd~
delayname]. Now make a feedback loop by connecting the [vd~ delayname]
back into the [delwrite~ delayname], and multiply this by a number less
than 1. Something between .9 and .99 will give you a good ringing sound.
The output of the [vd~ delayname] also gets sent out to the [adc~] for
you to hear.

Divide the samplerate by the frequency you want the comb filter to
resonate at, then divide by 1000 to get the delay length to send to the
[vd~ delayname]. It would be good to put your [delwrite~] and [vd~]
objects in a subpatch with a [block~ 1] object, which sets the blocksize
to 1 and allows for the shortest possible delay times [which in turn
gives you the highest possible resonant frequencies].

To make a resonant series, make multiple instances of this [as
abstractions, don't forget to use \$0 in the "delayname"!], and send the
base frequency to the first comb filter abstraction, and multiplications
or divisions of that to subsequent "harmonic" subpatches. Integers
[2,3,4...] will produce clean harmonics, while other numbers [.98, 1.34,
2.22...] will be detuned to various degrees, resulting in an acoustic
"beating" phenomenon as waveforms amplify and cancel each other out.

The same audio input is sent to all the comb filters. Sharp, percussive
sounds will "ring" the filters, giving you a plucked-string kind of
sound. Continuous sounds give something like a guitar or sitar type of
drone. Try changing the multipliers of the "harmonic" filters for
different drone or tonal effects.

All in all, I find it is much better for people to understand the
principles of how these things work, so building your own will be great
practice! Google for "karplus-strong" for more technical/mathmatical info.

Good luck,
derek

pun chik wrote:
> hi . can u send me an example patch of this harmonic series of resonant
> comb filters...im really interested in learning this. an example patch
> would be really nice
> many thanks
> punchik
>
> On Tue, 08 Feb 2005 18:11:04 +0100, "derek holzer" <derek at x-i.net> said:
>
>>Hi Marcus,
>>
>>marcus estes wrote:
>>
>>
>>>I'm a big fan of the Keith Fullerton Whitman album "Playthroughs,"
>>
>>Me too! I got a similar effect by using a harmonic series of resonant
>>comb filters triggered by contact mike input. The mikes are attached to
>>various bits and bobs I found in the Amazon... shells, plants, bones and
>>other unidentifiable stuff that produce nice sounds when plucked,
>>scraped or bowed. The comb filters are run through a granulating
>>feedback delay that makes "clusters" of particles similar to what you
>>hear on "Playthroughs" or "21:30 for Acoustic Guitar". Three or four
>>delays set at irregular intervals [i.e. 3/4, 7/5, 5/9, etc] add further
>>texture.
>>
>>
>>>I'm also a big fan of Derek Holzer's Particle Chamber patch.
>>
>>Thanks! ;-)
>>
>>
>>>I have considered re-tooling the Particle Chamber for use with a live input,
>>>but that seems a bit tricky.
>>
>>It's not too hard, really. Particle Chamber reads from static tables,
>>grabbing sections of loaded soundfiles and playing them back. I've built
>>a few adaptations for myself of this idea using delay lines instead of
>>tables, and they perform on input audio in the same way. I just haven't
>>cleaned them up for release yet. But if you compared the "guts" of each
>>patch, you would find them almost identical except for the source of the
>>sound. The mechanics remain pretty much the same. Play around with that
>>for a while, and I promise to clean up my own version sometime in March
>>for public release.
>>
>>best,
>>derek
>>
>>
>>--
>>derek holzer ::: http://www.umatic.nl
>>---Oblique Strategy # 36:
>>"Consult other sources
>>-promising
>>-unpromising"
>>
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--
derek holzer ::: http://www.umatic.nl
---Oblique Strategy # 36:
"Consult other sources
-promising
-unpromising"

```