"Rui Nuno Capela" <[EMAIL PROTECTED]> writes: > Thankyou Clemens. And also everyone else who kindly replied to this query. > > Clemens Ladisch wrote: > > > > 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. > > OK I see. > > I can live with the latency thing, but not with jitter nor silence :)
I don't recall any reports of a USB device working really *well* with JACK. Has anyone gotten satisfactory results (even at high latency)? > BTW Is firewire/ieee1394 based specifications any better? Can't remember > if ALSA has anything to do with it. We will have to do something about this isochronous device issue. There is an open bug report on it. I am willing to work on it, but... (1) I'm busy doing other things, and (2) I don't own any such device to test with. Has anyone had any success with JACK and Firewire? I might be willing to buy a Firewire audio device (depending on cost). Good luck with your purchase. Perhaps the situation is not as dark as some reports imply. -- joq ------------------------------------------------------- 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
