[LAD] Rate of change damping in digital mixer controls

Fons Adriaensen fons at linuxaudio.org
Wed Jan 29 02:44:18 UTC 2014

On Tue, Jan 28, 2014 at 03:34:39PM -1000, Joel Roth wrote:
> If I understand correctly, this click is the consequence of
> an unfiltered step in the waveform that carries a lot of
> harmonics.
> So I'm wondering how digital mixers and DAWs deal with this.
> Do they provide rate-of-change damping just for pan and
> volume faders, or perhaps some generalized rate damping on
> all parameters?

A pro-quality digital mixer will be designed to avoid clicks
and zipper noise on all controls. Even on/off functions will
be replaced by short fades.

All plugins should internally smooth their parameters when
a step change would generate artefacts and these would be
unexpected for that type of plugin. There is no such thing
as 'generalised rate damping'. It has to be done by the
plugin code and not by the host because

1. only the plugin (or rather its author) knows what is required
  (it depends on both the function and the actual algorithm),  

2. expecting a plugin to use already smoothed parameters (which
   would have to be audio rate) can make them very inefficient. 

As an example of [2], calculating the actual filter coefficients 
corresponding to the user parameters typically requires much more
complicated calculations than the real filter algorithm. So any
interpolation is done on the internal filter coefficients instead
of the user parameters. In some cases doing that requires the user
parameters to be rate-limited first.



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