[linux-audio-dev] Paper on dynamic range compression

[Paul Winkler]

On Wed, Oct 18, 2006 at 08:28:15AM +1000, Erik de Castro Lopo wrote:
> Dan Mills wrote:
> > --- Erik de Castro Lopo <mle+la at mega-nerd.com> wrote:
> > 
> > > You need a low pass filter on the control signal. It
> > > should
> > > be somewhere well below 1kHz.
> > 
> > Agreed that you need the filter, but a 'brick wall' at
> > 1Khz means that anything faster then 50ms or so as an
> > attack time (and there are legit uses for such), will
> > itself overshoot horrribly due to the gibb effect of
> > bandlimiting the control signal.
> 
> This is the way analogue compressors work. If you have a 
> sound with a fast transient going into a slow attack 
> compressor, the transient passes throught pretty much
> untouched (apart from any clipping that may occur due
> to other parts of the design).

Conversely, I'll just mention that it's possible to get distortion of
low-frequency audio by setting the release time extremely fast, because
the compressor is effectively trying to increase the gain at the end of
every half-cycle.  This is considered a case of giving the engineer
enough rope to hang himself, and hoping that he uses it responsibly. See
http://www.fmraudio.com/FAQ.htm#question4
for more.

-- 

Paul Winkler
http://www.slinkp.com