[PD] change in compression detection

Ludwig Maes ludwig.maes at gmail.com
Mon Jan 10 12:21:04 CET 2011

Or more generally, watch the histogram of samples

On 10 January 2011 11:09, Roman Haefeli <reduzent at gmail.com> wrote:
> On Sun, 2011-01-09 at 20:26 -0500, Mathieu Bouchard wrote:
>> On Mon, 10 Jan 2011, ~E. wrote:
>> > I'm searching how i can detect the change in the compression of an audio
>> > signal. The purpose is to detect (and quantified) the compression
>> > changes between the music and the ads in a radioshow. Have any ideas ?
>> If you don't have the original uncompressed recordings, I don't see how
>> you could be doing that. You'd have to guess how complex sounds are
>> supposed to fade out normally, to find out how much the fade out has been
>> messed with.
>> And then, in the compressor, you have both a measurement of input volume
>> and a formula for turning that input volume into a gain to be applied, and
>> both of those parts are subject to a lot of variation and tweaking.
> Assuming that the more compression is applied, the more the RMS
> amplitude [1] approaches the Peak amplitude [2] of an audio signal, you
> could measure the two and probably get a raw grasp how much compression
> was applied. This is simply an idea for which I don't have any reference
> that it is really working.
> I could imagine that recordings of certain sets of natural instruments
> show always a similar relation between peak and RMS amplitude for that
> set. However, usually there is already some compression applied when
> releasing the recording which makes it hard to distinct compression
> applied in the radio station from the compression shipped with the
> recording. I also could imagine, that it's much harder to find
> applicable rules for synthesized sounds.
> Roman
> [1] http://en.wikipedia.org/wiki/Amplitude#Root_mean_square_amplitude
> [2] http://en.wikipedia.org/wiki/Amplitude#Peak_amplitude
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