How can I use multiple soundcards with JACK?
JACK is fundamentally designed to be a component in a pro-audio/music creation environment and standard operating practice for such setups involves using only a single digital sample “clock” (something counting off the time between audio samples). This means that trying to use multiple independent soundcards is problematic, because each soundcard has its own sample clock, running independently from the others. Over time, these different clocks drift out of sync with each other, and cause glitches in the audio. You can’t stop this drift, although in some cases the effects may be insignificant enough that some people might not care about them.