On Wed, Jul 17, 2013 at 05:21:12PM +0200, IOhannes m zmoelnig wrote: > when running zita-a2j resp. -j2a in verbose mode, i understand that > the 1st number (the "loop error") should be as close to zero as possible. > in practice they are varying wildly betweeen +16 and -10. > how bad is this?
It's not that bad, it just indicates that there is some timing jitter. This can happen for a variety of reasons, see below. > more troubling however, is that whenever i start an alsa application > (e.g. alsa_delay), one or both zita-*2* applications complain with: > > Detected excessive timing errors, waiting 15 seconds. > This may happen with current Jack1 after freewheeling. You could try playing with the value in jclient.cc, line 437 to avoid this. Note that the delay error value printed by -v is averaged over 1/4 second, while the one tested is not. > (btw, i'm using robin's jackd2-1.9.10+nobus+20130114gite4730c6c-NMU1) > after 15 or so seconds the waiting application recovers, only to > hick-up again after some seconds (see end of email). > > i'm running the programs as follows: > jackd -dalsa -dhw:0,0 -r44100 -p1024 -n2 > zita-j2a -v -d hw:Loopback,0,1 -c2 -r44100 -Q16 -p2048 -n2 > zita-a2j -v -d hw:Loopback,0,0 -c2 -r44100 -Q16 -p2048 -n2 > alsa_delay hw:Loopback,1,0 hw:Loopback,1,1 44100 2048 2 This is really a combination of all possible worst-case scenarios. * Does your HW have a high resolution timer that Jack can use for its microseconds timer ? If not there will be trouble. * Same for the aloop device. It emulates a HW device at some configured sample rate, and therefore depends on an accurate timer in order to do this without loads of jitter. * I have *no* idea of the correct implementation of the DLL used in Jack2, but zita-ajbridge does critically depend on it. * For anything USB, 44.1 kHz is really asking for trouble. With 48 kHz you have at least a a simpler relation to the USB interrupt rate of 1 kHz, and if that doesn't help using -n 3 probably will. I don't know 'Andrea Electronics'... * Keep in mind that zita-ajbridge was not designed to be used this way. Its primary use is to add an additional (decent) soundcard to Jack, and I have my doubts about aloop. > finally: i'm wondering a bit on how to choose proper values for > period-size and fragement size. > that is: should zita-*a* period/nfrags match those of jack and/or > those of alsa_delay? For Jack vs. zita-*2* there are no restrictions. In normal use (that is adding a real sound card to Jack), you would make the period size of zita-*2* shorter than the one used by Jack (unless that is already quite small) to avoid additional latency. I don't know how having different period sizes on both ends of an aloop would affect it. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
