Subject: Re: [linux-audio-dev] ardour, LADSPA, a marriage
From: David Olofson (david_AT_gardena.net)
Date: Tue Nov 14 2000 - 11:23:25 EET
On Mon, 13 Nov 2000, Paul Barton-Davis wrote:
> >> > > * resonator(s)
> >> >
> >> > I don't know what one is, but there are a lot of papers on them about.
> >>
> >> I have a 12 db/oct variant built around an algo I found in one of
> >> these DSP algo sites. It needs replacing the coefficient
> >> calculations (trig funcs) with faster approximations, and linear
> >> interpolation of the coefficients, at least if it's goinng to be
> >> modulated.
> >
> >>From what I've read, aren't resonators just short, tuned delay loops with
> >variable feedback?
>
> the kinds of things i was thinking of were the streson opcode from
> Csound and the GaverHit module/opcode in Quasimodo. i haven't looked
> at their implementation, but the result is that you set the excitable
> frequency of the object (and possibly the "width" of the response),
> pass a signal through it, and it resonates if there is any energy in
> the response range. i don't know if you do this stuff with delays or
> not. i guess so, it just a filter system, right ?
Well, my experience is that this is exactly how resonant filters in
synths react, but when it comes to implementations, I think the most
common variant is to set up various kinds of IIR or state variable
filters that aren slightly "unstable" - or: resonant.
If you've tried building a very narrow analog bandpass filter, you
probably know how similar it is to an oscillator; it's very easy to
get self oscillation rather than filtering, and if there are
tendencies of that, it's triggered when you feed it with a signal
that's close enough to the passband. If the resonant is strong
enough, the oscillation will continue even if you remove the input.
(Musical applications usually don't allow that strong resonance.)
//David
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