Re: DynamicsCompressorNode no automatic make up gain

As a user of the API, I'd love a switchable make up gain, as this is a
useful feature but not something you'd want all the time.  Also, it would
be ideal if the exact implementation of the make-up gain were precisely
specified.

Thanks,
-Russell


On Mon, Jul 7, 2014 at 1:00 PM, Paul Adenot <paul@paul.cx> wrote:

>  On Mon, Jul 7, 2014, at 06:23 PM, Raymond Toy wrote:
>
>
>
>
> On Thu, Jul 3, 2014 at 7:18 PM, Robin Reumers <robinreumers@gmail.com>
> wrote:
>
> Hi all,
>
> For educational purposes, I used the DynamicsCompressorNode to teach
> compression. However, the DynamicsCompressorNode in the Web Audio API uses
> some sort of automatic make up gain, so it’s not just compressing above a
> threshold, but actually taking the soft parts up.
>
>
> I don't quite understand what this make-up gain is, but originally the
> DynamicsCompressor node had an emphasis and de-emphasis filters for high
> freuqencies that would cause the compressed audio to have a gain applied.
>  See the discussion at
> http://lists.w3.org/Archives/Public/public-audio/2014JanMar/0010.html.
>
>
> Make-up gain is a feature present in most hardware and software dynamic
> compression unit, that adds a gain stage after the compression stage, to
> bring the level back to where is was, often within a window.
>
> This can be useful (and this behaviour is most of the time configurable
> using an on/off switch), because sometimes, the input signal is simply too
> loud, and you want to harmonize the levels, but you don't want the gain
> stage afterwards, because you intend to have another mixing stage where you
> bring the level up independently of the input level.
>
> In other occasions, you just want to harmonize the levels, so the make up
> gain is an easy way to do that, because it tracks the input level
> automatically. Think of a singer that just did a voice track, but at some
> point in the performance, she moved a bit further from the microphone: you
> just apply a compressor with make up gain, and you've got your levels right
> (the reality is often more complex than that, but that's the idea).
>
> We could implement that either by having a `makeUpGain` property that
> would default to true.
> We should be able to implement make up gain using the `reduction`
> AudioParam, but I'd have to check to make this this is appropriate (in
> terms of windowing, etc.).
>
> That reminds me of the issue where we can't implement side-chaining, but I
> was planning write a proposal to the group when I'll write the spec text
> for the DynamicCompressorNode.
>
> In any case, I agree this is something we need, especially now that we
> have more and more complex applications that use real instruments audio
> tracks, recorded live in the browser (like this year's Google I/O
> conference). It could certainly be useful for WebRTC as well, as it would
> make it dead easy to write some custom Web Audio API code that would
> harmonize levels.
>
> Any thoughts?
>
> Paul.
>