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Re: Web Audio API sequencer capabilities

From: Chris Rogers <crogers@google.com>
Date: Mon, 8 Oct 2012 12:30:43 -0700
Message-ID: <CA+EzO0mZLvKFNX3_Nh8xkmXGRQ-RpQ1vH6f4QJ+wNM4F2-7a9w@mail.gmail.com>
To: Patrick Borgeat <patrick.borgeat@gmail.com>
Cc: Joe Berkovitz <joe@noteflight.com>, Jussi Kalliokoski <jussi.kalliokoski@gmail.com>, Srikumar Karaikudi Subramanian <srikumarks@gmail.com>, "public-audio@w3.org Group" <public-audio@w3.org>
On Sat, Oct 6, 2012 at 1:09 AM, Patrick Borgeat

> I'm having a related problem at the moment with
> setValueCurveAtTime, having a hard time figuring out how to scale a
> normalized Float32Array (values from 0 to 1) to another range (say, for a
> frequency from 2000 to 3000). Off course this could easily done in
> JavaScript but I'd prefer to generate just one Array for each curve at
> startup and scale it in the API, since it already can scale it in time.
> Scaling a signal is pretty easy: Put the signal through through a Gain
> with value 500, patch it into the param, and set value to 2500 (it now
> should oscillate between 2000 and 3000).
> Since the GainNode doesn't produce a signal we would need to feed him a
> Unity signal, but all the possibilities I see in the API would require the
> developer to specify the lifetime of the unity signal (I think it would be
> more straightforward for a UnitySourceNode to be collected automatically).
I think Joe already mentioned this, but if an AudioBufferSourceNode is in
"loop" mode, then it's not necessary to manage it's lifetime, and it will
simply play forever until gc.  Also, if an application often needs to deal
with these "unity sources", then it's pretty easy to just create a single
one, then share it among any nodes needing it.

> Easiest way for the setValueCurveAtTime would to have 2 additional
> parameters, a mul and an add (this is common in SuperCollider for example),
> with a formula like value * mul + add. As mul could default to 1 and add
> default to 0 you wouldn't need to set it if you don't need it.
Adding these optional parameters to setValueCurveAtTime() seems quite

> Mut maybe a more general Mul/Add scheme for AudioParams could be found,
> such as a mul/add parameter, which would be applied to any value change.
> Again, with defaults of 1 and 0 it
I was looking at the other AudioParam scheduling methods such as
setValueAtTime(), and it seems like it's already trivial to call them like:

param.setValueAtTime(value * mul + add, time);

It's useful for the setValueCurveAtTime() method, since the operation needs
to happen for all values in the curve, but for the other methods, it seems
easy to do with the existing API.
Received on Monday, 8 October 2012 19:31:11 UTC

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