Re: DynamicsCompressorNode no automatic make up gain

I think (as I have for some time) side-chain and noise gating should be in
v1.  :)


On Mon, Jul 7, 2014 at 10:02 PM, Hongchan Choi <choihongchan@gmail.com>
wrote:

> this is a useful feature but not something you'd want all the time.
>>
>
> Is asking the "side-chain" feature for the compressor too much? As far as
> I can tell, side-chain can't be implemented with the current version of API
> (except for ScriptProcessor node) since we do not have direct access on the
> level detector of compressor node. Currently GR is all we can get and it
> exists only for visualization/metering.
>
> As you already know, auto make-up or side-chain is not really rare in the
> real studio setup.
>
> Best,
> Hongchan
>
>
>
>
> On Mon, Jul 7, 2014 at 11:24 AM, Russell McClellan <russell@motu.com>
> wrote:
>
>> 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.
>>>
>>
>>
>
>
> --
> Hongchan Choi
>
> PhD Candidate, Research Assistant
> Center for Computer Research in Music and Acoustics (CCRMA)
> Stanford University
>
> http://ccrma.stanford.edu/~hongchan
>