[LAU] automatic gain control

[Fons Adriaensen]

On Tue, Aug 11, 2009 at 09:18:59AM +1000, James Cameron wrote:

> I've been asked to look into making an autonomous sermon recording
> device that will be attached to a monitor output of a front of house
> public address system.
> 
> I'm probably going to write it in Python with either a gstreamer or ALSA
> interface ... but getting to my question ...
> 
> ... is anyone aware of an automatic input gain control filter that can
> be applied, that will change the capture levels on the card, to ensure
> that peaking is avoided yet a reasonable amount of signal is captured?

With a decent audio card you should be able to set the HW gain
so that there's no overload ever, and do the rest of the processing
on the digital signal. Many cards have stepped mixer gains anyway,
making it more or less impossible to use the mixer settings for auto
gain control. 

For the processing a slowly acting compressor should do the trick.
Best would be one with a 'hold' function, to prevent it raising
the gain if there is a longer pause. 

Ciao,


-- 
FA

Io lo dico sempre: l'Italia è troppo stretta e lunga.