Hector Martin

Recent problem I had: You have two .wav files. You're playing through an external sound card. 'A' always plays fine. 'B' plays sometimes, and sometimes not, randomly. If you play *both* at once, it makes no difference: you always hear 'A' and sometimes 'B' mixed in.

You're using 2 channels on the interface (files are stereo). It has a hardware level meter. The level meter always shows activity (in both L/R channels), even when playing 'B', regardless of whether it worked that time or not. When playing both files, mixing is done in software.

It's not a stereo cancellation issue: you can hear both channels and it doesn't sound like 'A' is suffering from cancellation. It's not a software channel routing issue: you've verified that both files mix into the same two main outputs, every time.