Re: Web Audio API Proposal

I have a pretty good idea how to make the optimizations, so we should be
good there.  Conceptually, I think Jer's idea is the simplest and most
transparent.

On Tue, Jun 22, 2010 at 4:20 PM, Chris Marrin <cmarrin@apple.com> wrote:

>
> On Jun 21, 2010, at 4:47 PM, Jer Noble wrote:
>
> >
> > On Jun 21, 2010, at 3:27 PM, Chris Marrin wrote:
> >
> >> On Jun 21, 2010, at 2:34 PM, Chris Rogers wrote:
> >>
> >>> Hi Chris,
> >>>
> >>> I'm not sure we can also get rid of the AudioGainNode and integrate the
> concept of gain directly into all AudioNodes.  This is because with the new
> model Jer is proposing we're connecting multiple outputs all to the same
> input, so we still need a way to access the individual gain amounts for each
> of the separate outputs.
> >>
> >> Right, but if every node can control its output gain, then you just
> control it there, right? So if you route 3 AudioSourceNodes into one
> AudioNode (that you're using as a mixer) then you control the gain of each
> channel in the AudioSourceNodes, plus the master gain in the AudioNode. For
> such a common function as gain, it seems like this would simplify things.
> The default gain would be 0db which would short circuit the gain stage to
> avoid any overhead.
> >
> >
> > Actually, I don't agree that modifying the output gain is so common an
> operation that it deserves being promoted into AudioNode.  Sure, it's going
> to be common, but setting a specific gain on every node in a graph doesn't
> seem very likely.   How many nodes will likely have a gain set on them?
>  1/2?  1/4?  I'd be willing to bet that a given graph will usually have as
> many gain operations as it has sources, and no more.
> >
> > I can also imagine a simple scenario where it makes things more
> complicated instead of less:
> >
> > <PastedGraphic-1.tiff>
> >
> > In this scenario, there's no way to change the gain of the Source 1 ->
> Reverb connection, independently of Source 2-> Reverb.  To do it, you would
> have to do the following:
> >
> > <PastedGraphic-3.pdf>
> >
> > And it seems very strange to have to create a generic AudioNode in order
> to modify a gain.  Alternatively, you could create multiple
> AudioReverbNodes, but again, it seems weird to have to create multiple
> reverb nodes just so you can change the gain going to only one of them.
> >
> > Right now, every AudioNode subtype has a discreet operation which it
> performs on its input, and passes to its output.  To add in gain to every
> AudioNode subtype would make things more confusing, not less.
>
> Ok, fair enough. My concern is that adding a gain stage will require extra
> buffering and extra passes through the samples. Do you think it will be
> practical for an implementation to optimize the gain calculation? For
> instance, I might have some software algorithm doing reverb. Since it's
> running through each sample, it would be easy for it to do a multiply while
> it's accessing the sample (either on the input or output side). If the
> reverb node knows it has a single input and that input is from a gain stage,
> it could do the gain calculation itself and avoid another pass through the
> data.
>
> As long as optimizations like that are possible, I think having a separate
> AudioGainNode is reasonable.
>
> -----
> ~Chris
> cmarrin@apple.com
>
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