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Re: ISSUE-5: pausing a subgraph

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 26 Mar 2012 16:25:29 +1300
Message-ID: <CAOp6jLZp2gnS4rr8iL4zCpre=nGeq+ecMOW7OANbahOizn80CQ@mail.gmail.com>
To: Chris Rogers <crogers@google.com>
Cc: olivier Thereaux <olivier.thereaux@bbc.co.uk>, public-audio@w3.org, jussi.kalliokoski@gmail.com
On Fri, Mar 23, 2012 at 8:44 AM, Chris Rogers <crogers@google.com> wrote:

> For dealing with arbitrary parts of the graph (sub-graphs or sub-mixes)
> one technique is to control the .gain parameter on an AudioGainNode which
> controls the overall volume for that part of the graph.  The gain/volume
> transition can be made suddenly or slowly faded out at precise times.
>  Another technique is to simply stop scheduling any new "notes" from
> playing in AudioBufferSourceNodes, and by stopping any currently playing
> notes by calling the noteOff() method.  Sometimes, it will be a good idea
> to schedule the noteOff() to not happen immediately, but to wait for the
> exact time that a loop reaches its end.
>

That's not pausing, just muting.


>
>
>> It seems to me that wouldn't be satisfactory. First of all, there are no
>> guarantees that explicitly pausing each input will pause them all at
>> exactly the same moment, so pausing and resuming would break
>> synchronization.
>
>
> AudioBufferSourceNodes can be scheduled to happen at exact times.  So
> their start and end times can be given precisely and will be synchronized.
>

I don't think that works for other sources such as media elements. Also,
you can't easily start playing an AudioBufferSourceNode in the middle of a
buffer to make it start playing again at the right point.

WHEN THE SOURCE IS RESUMED
> When paused according to (1)
> 1a. The echo/reverb is heard from old (before pausing) sounds played by
> the source, layered on top of echo/reverb from the new (resumed) sounds
> from the source.
>


> 1a is considered to be anomalous behavior in musical applications since it
> abruptly re-introduces old/stale echo/reverb state into the rendered audio
> stream.  It can be caused by a filter (echo/reverb in this case) not having
> its state reset properly at the moment of "pausing" for case (1).
>

1a is clearly desired if you're pausing output of the entire application,
or (per
http://lists.w3.org/Archives/Public/public-audio/2012JanMar/0297.html)
you're pausing part of the application. I suppose the question is whether
there are interesting use-cases where the graph to be paused is not the
whole graph.

Rob
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Received on Monday, 26 March 2012 03:25:59 GMT

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