I believe Timidity++ just uses its synthesizer to convert the MIDI information into an audio stream, which it then either writes to a file or plays through the soundcard. So it doesn't need precise timing, since the audio callback it uses is already timed by the sound system. When dealing with real MIDI, timing is more critical, though usually you simply use timestamps which tell the sound system when a MIDI event should be played, instead of dealing with the timing yourself. (At least I know this is the case with PortMidi, I've never programmed with ALSA directly.) By the way, there are more ways to time things than just *sleep(). For example, using sigalrm and setitimer. Don't know anything about that. I think all soundcards use an built-in timer for playing their FIFO. As for interrupting the computer to tell it when it needs more data, I guess it's possible that sometimes it uses the card's timer and sometimes uses the system timer. Someone more informed may have something to say. Steve

Mulyadi Santosa wrote: Most sound cards don't have an internal timer that could be used for MIDI timing. ALSA uses whatever timer is configured, the default for this is the RTC timer. HTH Clemens