Rui Nuno Capela wrote: > As a followup on this subject (see below) I've come near to a decision > about the EDIROL UA-20, but still don't know if there's any specific issue > with JACK for this USB adapter.
There isn't any specific issue with the UA-20, but with USB devices in general. What all USB devices have in common is that audio data is moved over the USB bus in frames, and that there are 1000 frames per second. So, a 48000 Hz stream would move 48 samples per frame, and a 44100 Hz stream would move 44.1 samples per frame. However, there are no fractional samples, so the frames would have 44 samples, with one out of ten frames having 45 samples. In theory, one USB frame could be equivalent to one period in ALSA, but ALSA assumes that period sizes are constant, and Jack further requires that period sizes are a power of two (which would be true for most other sound cards). Because of this, ALSA's USB driver sometimes double-buffers audio data, and emulates arbitrary period sizes on top of the USB frames. The consequence of all this is that you have to use larger period sizes and/or more than two periods per buffer with Jack, which will slightly increases your latency. Regards, Clemens ------------------------------------------------------- The SF.Net email is sponsored by EclipseCon 2004 Premiere Conference on Open Tools Development and Integration See the breadth of Eclipse activity. February 3-5 in Anaheim, CA. http://www.eclipsecon.org/osdn _______________________________________________ Alsa-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-user
