Re: Directly setting biquad coefficients

That's CLEARLY an application for a custom worker.  Or a completely
separate node.  :)

The current biquad filter node only applies its parameters at k-rate.  I'll
ask the same question I asked Raymond - should we just make this a separate
node, so we can more carefully define custom behavior (and not have the
params like frequency, detune, gain, Q that don't apply to a custom filter?)

On Wed, Oct 8, 2014 at 9:03 AM, Norbert Schnell <Norbert.Schnell@ircam.fr>
wrote:

> Whoopee!!! Great idea (in meantime we didn’t dare asking again :-).
>
> On 08 Oct 2014, at 17:22, Raymond Toy <rtoy@google.com> wrote:
>
> Chris and I were discussing the possibility of allowing a user to set the
> coefficients of a biquad filter directly, as mentioned in
> https://github.com/WebAudio/web-audio-api/issues/323
>
> This ability makes it possible to have a first-order filter, which isn't
> possible now. This also makes it easier to create higher-order filters from
> biquads where you've decomposed the filter into a set of biquads with the
> coefficients. No need to convert each biquad into a lowpass, bandpass, and
> highpass filter with appropriate frrequency and Q values.
>
> We think this is a good idea, but were not sure on exactly how to expose
> this.
>
>    - Should we have setCoefficients(b0,b1,b2,a1,a2) create a "custom"
>    filter type?
>       - This would preclude any kind of automation.
>       - The values of frequency, Q, gain would be undefined (in some way)
>       for this filter type.
>    - Should the individual coefficients be exposed as audioparams?
>    - We couldn't come up with an actual use-case where any one would
>       want, say, a linear ramp for, say, coefficient a1
>       - Some possibly interesting filtering affects might be possible.
>
> Thoughts?
>
>
> I clearly would vote for the second (the audio parameters).
> For many time variant filters it makes sense to update the coefficients
> with a more sophisticated algorithm on one rate (e.g. every few
> milliseconds) and add linear transitions between successive sets of
> coefficients in audio rate to generate smooth filters.
>
> N.
>
> _____________________
> N o r b e r t   S c h n e l l
> { Sound Music Movement } Interaction
> IRCAM – Centre Pompidou
>
>