Tobias, I wrote a program that does just this some years ago for IED (www.iedaudio.com). What you are doing is not trivial. When an announcement starts on the left channel (for example) you will want to fill the right channel with zeroes. However you must fill the buffers in small blocks so that if an announcement starts on the right channel, you can start stuffing the right channel without a long delay. You might want to investigate Paul's program JACK for this. It splits the audio into separate buffers for each I/O. If you really have to have it ASAP, why not just buy an IED system? :) -Ben