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Re: DynamicsCompressorNode no automatic make up gain

From: Hongchan Choi <choihongchan@gmail.com>
Date: Mon, 7 Jul 2014 09:54:13 -0700
Message-ID: <CAH8-aR1kOiDS_Xz6-nzjOCcJyNjWBrfAtCwsQfMK9Wf9bzQvVg@mail.gmail.com>
To: Raymond Toy <rtoy@google.com>
Cc: Robin Reumers <robinreumers@gmail.com>, "public-audio@w3.org" <public-audio@w3.org>
Hello Ray and Robin,

I guess the relevant part is this:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/platform/audio/DynamicsCompressorKernel.cpp&l=233

What I can see is the post gain processing is not transparent. However, I
do not believe this is a complete automatic makeup mechanism either. (there
is no consideration on envelope/knee and etc). The comment also says
"*Empirical/perceptual
tuning*," so I was told the intention behind this implementation is to make
the compressor node sound good out of the box. The issue on de-emphasis is
in the same vein.

I thought the same thing with Robin before - there should be a way to turn
off the post gain processing. However, it would be great to have automatic
makeup and side chain (since they are not easy to implement on JS level),
but IMHO making it transparent should be the first.

Best,
Hongchan




On Mon, Jul 7, 2014 at 9:23 AM, Raymond Toy <rtoy@google.com> 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.
>
> If this is what you are seeing, then this should have been removed and
> Chrome 36 should have this fix.
>
>
>
>> For education, it’s important, that I can show this manually to my
>> students, so compression is basically taking the down the signal, above the
>> threshold, by the ratio. Then using a manual make up gain, I can offset why
>> I just compressed and bring all the levels up.
>>
>> Is there a way to turn off the automatic make up gain added by the
>> DynamicsCompressorNode? I tried linking the reduction meter with a gain
>> offset and doing the exact opposite gain of the reduction, but this only
>> results in glitches and I can’t get it to work properly.
>>
>> Any ideas would be welcome.
>>
>> Best wishes,
>>
>> Robin
>>
>
>


-- 
Hongchan Choi

PhD Candidate, Research Assistant
Center for Computer Research in Music and Acoustics (CCRMA)
Stanford University

http://ccrma.stanford.edu/~hongchan
Received on Monday, 7 July 2014 16:55:00 UTC

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