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Web Audio thoughts

From: Ray Bellis <ray@bellis.me.uk>
Date: Tue, 12 Jun 2012 17:21:52 +0100
Message-ID: <4FD76CA0.3030408@bellis.me.uk>
To: public-audio@w3.org
Hi Chris & co

I've been looking at your work on the Web Audio API and been
experimenting a little with it.

My current goal is to produce a virtual modular synthesizer using Web
Audio.  To that end, I'm building a framework where I can create a
visual graph of AudioNodes and connect them together.

The current (but *very* early) work in progress is at
<http://alnitak73.dyndns.org/> and requires Chrome Canary because the
stable Chrome version doesn't include an Oscillator.

It's only 200 lines of code at the moment, but with that I'm able to
wrap an arbitrary AudioNode into a visual representation showing its
inputs, outputs, and any AudioParam properties it has.  Outputs of nodes
can be clicked on and then connected to inputs and AudioParams of other
nodes.

To make a full synthesizer I need to build additional pseudo-nodes to
represent things like envelope generators and other control signals -
equivalents to CV and gate, as it were.

I will also need to find ways to describe the controls to existing nodes
that aren't managed by AudioParams, such as the impulse response for a
ConvolverNode, or the filter mode for a BiquadFilterNode.

In any event, I think I can see some things that would be useful, but
that don't appear to be available in the current API:

1.  AudioParam variables

There's no way I can see to have an AudioParam property in a
JavascriptAudioNode and then have that node sample the parameter.  The
JS node is very useful, but without access to AudioParam features it's
kind of a second class citizen.

For example I might want to implement my ADSR EG using a JS AudioNode.
In "real" synthesizers it's common to have the ability to tweak the ADSR
envelope based on input frequency.  I don't think I can do that with the
current API.

I can't even implement a custom JS oscillator that has the same external
interface as the standard Oscillator without access to AudioParams.

2.  More fine-grained "disconnect"

With the current API and my framework I can connect specific outputs to
specific inputs, but the API only allows for disconnecting _every_ link
from a specific output.  This feels like a significant limitation.

3.  Interrogation of the node graph

It would be really handy to be able to ask the AudioContext (or
individual nodes) for their list of connections.

I'm not sure how well that sits with "one shot" generator nodes seeing
as they automatically disconnect themselves, though...

I'd appreciate your thoughts on these, and apologise if they've already
been covered or otherwise addressed in the mailing lists.

cheers,

Ray Bellis
Received on Tuesday, 12 June 2012 16:51:16 GMT

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