Re: [webaudio] possible error in DRC processing graph

That was my expectation as well (and what you're saying sounds logical to
me), but we've largely inherited code that was already running, and had to
retro-specify it.

Here is the code we had to work from, for reference:

-
https://searchfox.org/mozilla-central/rev/ff82c973f8ccb0475ec32439e9ec07014b3a681f/dom/media/webaudio/DynamicsCompressorNode.cpp#88
-
https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/platform/audio/dynamics_compressor_kernel.cc;l=189;drc=d0e87c5b5ac8f1d884f5899f4b63967fea784d07

the WebKit code was forked by Mozilla long ago because there was no
specification, and it was already shipping in Chrome and Safari, and we had
to ship a compatible DynamicsCompressorNode. Style has diverged but this
bit is the same.

Hope this helps,
Paul.

On Mon, Nov 16, 2020 at 4:44 PM Curtis Malainey <cujomalainey@google.com>
wrote:

> Thanks Paul,
>
> I am not 100% sure about the second graph. Isn't the knee the width around
> the threshold? The first graph in my mind looks correct if you just move
> the threshold forward to the hard knee so the curves remain the same after
> the knee. Otherwise it looks like you are factoring in a boost post
> threshold which seems to be the opposite of a compressors purpose. See
> slide 10 (ignoring overall boost)
> http://c4dm.eecs.qmul.ac.uk/audioengineering/compressors/documents/Reiss-Tutorialondynamicrangecompression.pdf
>
> That being said, don't take my word at face value, I am trying to fix some
> of our compression curves and making sure I understand this enough before I
> do it.
>
> Curtis
>
> On Mon, Nov 16, 2020 at 3:53 AM Paul Adenot <padenot@mozilla.com> wrote:
>
>> Yes, you're right, I don't know why I did it like that in the first place.
>>
>> Thanks for the report, I've updated with a new proposed diagram:
>> https://github.com/WebAudio/web-audio-api/pull/2277
>>
>> Paul.
>>
>> On Mon, Nov 16, 2020 at 6:11 AM Curtis Malainey <cujomalainey@google.com>
>> wrote:
>>
>>> Hello w3
>>>
>>> I was browsing the DRC web audio spec and I believe there is an error in
>>> the graph in section 1.19.4 figure 14. The graph denotes the difference
>>> between a hard and soft knee. But shouldn't a hard knee be on the threshold
>>> marker? The figure has the threshold marker at the beginning of the soft
>>> knee.
>>>
>>> Curtis
>>>
>>