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Re: Web Audio API questions and comments

From: Chris Wilson <cwilso@google.com>
Date: Tue, 19 Jun 2012 09:34:22 -0700
Message-ID: <CAJK2wqUcG+w_8ove+otOUt3_O1ZgsyjAm48FGc_404Uj2gVbPw@mail.gmail.com>
To: Joe Turner <joe@oampo.co.uk>
Cc: public-audio@w3.org
Hey Joe - I can respond to a couple of these.

On Tue, Jun 19, 2012 at 7:39 AM, Joe Turner <joe@oampo.co.uk> wrote:

> - Operator nodes, AudioParam nodes
> Can we have separate nodes for the basic mathematical operators (add,
> subtract, divide, multiply and modulo), and a way of having the output
> of an AudioParam as a signal?  This would allow all the flexibility
> needed for scaling, offsetting and combining signals in order to
> control parameters.  I know a bit of trickery can make stuff like this
> possible at the moment, and it's trivial to implement in JavaScript,
> but it seems like core functionality to me.

Actually, you should be able to do all of these operations by either
connecting nodes together (add and subtract - might need a waveshaper to
flip phase for subtract), using gainNodes (multiply and divide) - not sure
about how you'd use modulo.

> - Tapping DelayNodes
> At the moment it's only possible to tap a delay line at the beginning,
> and the read position cannot be modulated.  This makes it pretty much
> impossible to implement effects such as pitch shifting, chorus,
> phasing, flanging and modulated reverbs, all of which rely on either
> multiple taps or modulated taps.  It would be nice to have something
> similar to Supercollider's BufRd [4] and BufWr [5] with DelayNode
> built as a layer on top of this.  Also AudioBufferSourceNode could be
> a layer on top of a BufRd equivalent.

Not sure what you mean - you should be able to build all these.  Remember
you can chain multiple delay nodes in series as well as in parallel.  For
chorus and flanging, I'm currently working on a code sample.

- AudioBufferSourceNode playbackState change event
> Would it be useful to have an event fired when the
> AudioBufferSourceNode's state changes?  I can't think of anything off
> the top of my head, but it seems like it could be useful for some
> applications maybe?

Actually, it would be interesting to do that; I've wanted to do cleanup
(e.g., change a play button's visual state back when the BSN finishes
playing), and I've currently hacked it by setTimout(buffer.duration*1000).
 That won't work when playbackRate is being manipulated, though.

> - AudioPannerNode
> Having never done any work in 3D sound I find this all a bit
> intimidating.  Is there any chance of something simpler built on top
> of this for those of us who want sound to come out of the left
> speaker, the right speaker, or some combination of the two?

I'll come up with a sample.  It's actually quite easy to do simple panning.

> - RealTimeAnalyserNode
> This seems strange to me - the functionality could be really useful,
> but it seems focused very narrowly on creating visualisations.  I
> think a nicer solution would be to have separate FFT and IFFT nodes so
> frequency domain effects could be integrated into the processing
> chain, and then a separate node which allows access to the FFT or
> waveform data depending on where in the graph it is inserted.  So for
> visualisations you would have an AudioNode connected to an FFTNode,
> connected to a BufferYoinkerNode.

This is actually about what realtimeAnalyser is.  What scenario are you
trying to do, exactly?

> - DynamicsCompressorNode sidechaining and lookahead
> I'm not sure if these are a bit specialised, a bit of a dark art, or
> both, but they are both common and fairly well defined features of
> compressors which may be useful.  I could see sidechaining being
> especially useful for ducking in broadcast applications.

Lookahead is different, of course.  Sidechaining could be accomplished by
connecting the 'reduction'  parameter of the DynamicsCompressor to a gain
node - although since reduction is an AudioParam, it can't get connected
anywhere.  That could be fixed by adding an AudioNode copy of reduction, I

Received on Tuesday, 19 June 2012 16:34:51 UTC

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