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Re: Multi-channel hardware support available for testing in Chrome Canary

From: Jory <me@jory.org>
Date: Fri, 15 Mar 2013 14:15:36 -0700
To: Jory <me@jory.org>
Cc: public-audio-dev@w3.org
Message-ID: <20130315141536424978.3833f468@jory.org>
I removed the panner node and suddenly I have 5.1 playback of my 
6-channel WAVE file! Yay!


On Fri, 15 Mar 2013 11:53:55 -0700, Jory wrote:
> Ah, so it was the panner that was messing with me. Are plans to make 
> the panner into a steerable multichannel one? I'm sure I won't be the 
> only audio developer to get thrown by this, as I'd have expected it 
> behave quite differently. I guess for the moment, custom panning code 
> has to be written to handle surround steering.
> I'll give your suggestions a try in a bit. 
> Thanks!
> Jory
> me@jory.org
> http://studio.jory.org
> On Mar 15, 2013, at 11:08, Chris Wilson <cwilso@google.com> wrote:
>> I will be writing a demo, yes.  As Chris said, to utilize the 
>> multi-channel output you really want to use ChannelMergerNodes - 
>> unless you're playing a source buffer node that is multichannel.
>> I'd point out text from the spec on AudioPannerNode: "The output of 
>> this node is hard-coded to stereo (2 channels) and currently cannot 
>> be configured."  You won't get surround-sound placement from 
>> Panners, at least not based on the current spec - similarly 
>> ConvolverNodes will never output more than two channels.  If you run 
>> a 6-channel source through one of those nodes, it would get 
>> downsampled to stereo.  This is mentioned in their respective 
>> sections, but also in Section 9:
>> // PannerNode and ConvolverNode are like this by default.
>> pannerNode.channelCount = 2;
>> pannerNode.channelCountMode = "clamped-max";
>> pannerNode.channelInterpretation = "speakers";
>> As for a 6-channel WAV file - well, I don't have a 6-channel system 
>> handy, but it should work.  I tested decoding a 6-channel WAV 
>> (sample from McGill: 
>> http://www-mmsp.ece.mcgill.ca/documents/AudioFormats/WAVE/Samples.html) 
>> and it worked fine.  As in the spec, if you had 5.1 hardware, you'd 
>> have to set this to get it to output correctly:
>> // Set ´hardware output¡ to 5.1
>> context.destination.channelCount = 6;
>> context.destination.channelCountMode = "explicit";
>> context.destination.channelInterpretation = "speakers";
>> Then connect the 6-channel BufferSourceNode to the context.destination.
>> The output.L, .R, .C in section 9.1 are misleading you - that is 
>> effectively pseudocode detailing how up/downmixing should be done 
>> between layouts.  Your "forced mono gets sent to the Center channel" 
>> is shown in that section:
>>     1 -> 5.1 : up-mix from mono to 5.1
>>         output.L = 0;
>>         output.R = 0;
>>         output.C = input; // put in center channel
>>         output.LFE = 0;
>>         output.SL = 0;
>>         output.SR = 0;
>> Simplistic version: you either need to 
>> work with original multi (>2) channel sources and set your "hardware 
>> output" to interpret as speakers - which case you need to be careful 
>> with nodes that downsample (Convolver and Panner), or 
>> set interpretation to "discrete", and make sure you're sending the 
>> correct number of channels to the output to fill up all the 
>> channels.  This would use mergers, and would also be the way you 
>> would implement a digital DJ app or other 
>> multiple-paired-stereo-outputs case (e.g. a DAW).
>> Either way, of course, you'll want to set the 
>> context.destination.channelCount to the desired number of channels, 
>> and the channelCountMode to "explicit".
>> Hope that helps,
>> -Chris
>> On Fri, Mar 15, 2013 at 10:47 AM, Jory <me@jory.org> wrote:
>>> I spent a lot of time reading through that part of the spec lat 
>>> night, but to no avail. I didn't try the ChannelMergerNode, so I'll 
>>> give that a shot.
>>> Something that was completely unclear to me was what output.L, 
>>> output.R, output.C, etc referred to. Where is output coming from? I 
>>> didn't see anything like that in any of the examples elsewhere, nor 
>>> could I found anything that subdivided channels inside the 
>>> Inspector in Canary.
>>> Also, should multichannel audio files play? If so, what formats?
>>> Jory
>>> me@jory.org
>>> http://studio.jory.org
>>> On Mar 15, 2013, at 10:34, Chris Rogers <crogers@google.com> wrote:
>>>> On Thu, Mar 14, 2013 at 11:11 PM, Jory <me@jory.org> wrote:
>>>>> On Thu, 14 Mar 2013 15:53:50 -0700, Chris Rogers wrote:
>>>>>> For those interested in multi-channel output in the Web Audio 
>>>>>> API, here's
>>>>>> your chance to try out an early build.  This could be of interest for
>>>>>> digital DJ type applications, or rendering to multi-channel speaker
>>>>>> installations...
>>>>>> Please note this is an early build and little testing has yet 
>>>>>> been made.
>>>>>>  So far I've tested on several devices on OSX.  I'm interested in your
>>>>>> feedback!
>>>>>> The .maxChannelCount attribute is now exposed to show the actual 
>>>>>> number of
>>>>>> hardware channels:
>>>>>> The .channelCount attribute should now be settable on the
>>>>>> AudioDestinationNode to values up to .maxChannelCount
>>>>>> Cheers,
>>>>>> Chris
>>>>> Well, I've spent a couple hours playing around, since multichannel
>>>>> audio certainly interests me, both for games and music. I've had very
>>>>> little success, though.
>>>>> I'm finding it very difficult to get any audio to play out anything but
>>>>> the Left and Right channels. The only success I've had was forcing a
>>>>> down-mix to 1 channel, where sound finally came out my Center channel.
>>>>> So clearly the system functions in some manner. I've tried setting up a
>>>>> 3D panner and hard-coding positional panning, but sound never leaves my
>>>>> Lft-Rht channels.
>>>> Hi Jory, I believe Chris Wilson will be writing an article with 
>>>> more details and complete sample code.  In the meantime, you can 
>>>> look at some of the partial example code here:
>>>> Just to add a little more detail, with the "digital DJ" example 
>>>> you'd want to use a ChannelMergerNode to combine two separate 
>>>> stereo mixes.  The first one would be connected to input 0 of the 
>>>> merger and the 2nd to input 1.  Then the merger would be connected 
>>>> to the destination as configured in the partial example code.
>>>> The ChannelMergerNode turns out to be really important for these 
>>>> types of applications.  In another example, if your hardware 
>>>> supported 8 channels of output, you could configure it as 
>>>> 8-channel discrete, then create a merger and connect eight 
>>>> independent mono AudioNodes to inputs 0 - 7 of the merger.  Then 
>>>> you could hookup eight speakers and place them anywhere in the 
>>>> room you like.  And the mono sources could be whatever you want - 
>>>> maybe 8 de-correlated channels of white noise...
>>>> Hope that helps.
>>>>> I also tried playing back a 6-channel interleaved WAV file, but while
>>>>> the file appears to "play", sound doesn't come from any speaker, no
>>>>> matter how I try to configure the channelCount.
>>>>> I'm beginning to wonder if 6-channel source files are playable at this
>>>>> time or if that's unsupported. (Everything seems to have choked when I
>>>>> supplied a 6-channel AAC file, but I'm not even 100% the file I
>>>>> supplied was even playable, since getting multi-channel AAC output is
>>>>> kinda challenging with today's tools.) Also, a bit of sample code would
>>>>> do my morale wonders right about now. :-)
>>>>> Thanks!
>>>>> Jory
>>>>> me@jory.org
>>>>> http://studio.jory.org


Received on Friday, 15 March 2013 21:16:06 UTC

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