Re: Directly setting biquad coefficients

Sorry, I forgot to add the option for a new node, even though we just
talked about it. :-(

I'm ok with a new node. Unfortunate that they would overlap in basic
functionality.

On Wed, Oct 8, 2014 at 9:15 AM, Chris Wilson <cwilso@google.com> wrote:

> 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
>>
>>
>