[linux-audio-dev] Silence Detection

[Conrad Parker]

On Thu, Oct 17, 2002 at 03:31:36PM -0400, Taybin Rutkin wrote:
> On Thu, 17 Oct 2002, David Arney wrote:
> 
> > I work with a small community radio station, and since we're continually
> > strapped for cash we implement our studio-transmitter link by streaming
> > audio over a network. We use a variety of players and formats (mainly xmms
> > and realplayer), but all of them share a common problem. Despite our
> > process monitoring software, the stream occasionally goes silent. We would
> > like to find a way to detect when the output of the playback computer's
> > soundcard is silent- or at least quiet enough to count as such.
> 
> Were you planning on using a noisegate algorithm?  I think you would have
> to.  One common mistake people make is thinking that silence is going to
> be all zeros.  But that's almost never the case when doing real work with
> analog equipment.
> 
> I'm not sure where to find an algorithm for that, but Steve Harris has
> many many open plugins at plugin.org.uk .

we've got some bits of code for doing that at CSIRO:

	* MPEG Maaate has an analysis plugin for detecting loudness
	  levels in the MPEG compressed domain:

	  http://www.cmis.csiro.au/maaate/
	
	* we did a "select by energy" plugin for Sweep that works on
	  PCM data by a similar algorithm; have a look at
	  plugins/byenergy/byenergy.c in the Sweep source distribution:

	  http://sweep.sourceforge.net/

(both are GPL)

Conrad.