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Re: Number of channels in the JavaScriptAudioNode

From: Chris Rogers <crogers@google.com>
Date: Tue, 3 Apr 2012 13:19:54 -0700
Message-ID: <CA+EzO0nUsgUMu1aAnDa56z-vgYjcc0WtVDxMvcf1Hm3bbBqQPA@mail.gmail.com>
To: Chris Lowis <chris.lowis@bbc.co.uk>
Cc: public-audio@w3.org
On Tue, Apr 3, 2012 at 8:31 AM, Chris Lowis <chris.lowis@bbc.co.uk> wrote:

> Hi,
> In the process of working up some simple synthesis examples, I've come
> across some behaviour I don't understand. Perhaps Chris, Raymond or someone
> familiar with the Web Audio API can help.
> I'm trying to create a JavaScriptAudioNode that adds two mono signals
> together (generated by my javascript node-based sine wave generator).
> When I execute:
>  context = new webkitAudioContext
>  node = context.createJavaScriptNode(**1024, 2, 1)
> I see that 'node' has
>  numberOfInputs: 1
>  numberOfOutputs: 1
> (at least in Chrome 18.0.1025.142)
> Is it possible at the moment to create javascript nodes with multiple
> inputs and outputs?
> In general what's a good way of working with mono signals? I admit to
> being a little unsure of the best way to use the various splitter and
> merger nodes.
> Best,
> Chris

Hi Chris, a JavaScriptAudioNode always has one input and one output (the
input can be ignored and not connected).  There's a distinction between
numberOfOutputs (which is always 1) and numberOfChannels (for this single
output).  For example in the real-world there are stereo 1/4" cables.  So
although it's a single cable (or bus) it carries two channels and can be
plugged into a stereo output jack.  Another real-world example is an HDMI
cable, which can carry 5.1 channels even though you plug it into a single
output connector on your surround-sound receiver.

I should point out that there *is* a bug in  createJavaScriptNode() in
WebKit where it silently ignores the 2nd two arguments (number of input and
output channels).  So in your example, you're wanting to output 1 channel.
 But, the implementation continues to generate 2 channel output.  But,
that's a bug - not how it's supposed to work.

Received on Tuesday, 3 April 2012 20:20:24 UTC

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