On 05/03/2012 04:26 AM, Joel Roth wrote: > On Tue, Apr 17, 2012 at 05:09:52PM +0000, Fons Adriaensen wrote: >> On Mon, Apr 16, 2012 at 05:21:47PM -0400, S. Massy wrote: >> >>> Okay, so for a standard 2 periods of 128 frames each, my nominal dddelay >>> is 256 frames or 5.3ms at a sr of 48k, twice that for a round-trip. >> >> No. The nominal roundtrip-delay (physical input to physical output >> if you connect the corresponding ports directly) is period * nperiods. >> >> 1 * period occurs at the input, (nperiods - 1) * period at the output. > > Thanks for clarifying this. > > I understand that the round trip delay for the soundcard is the sum > of capture port latency and playback port latency, plus whatever > additional delay is associated with the AD/DA converters. > > However I see what appears to be a discrepency for > the latencies reported by jackd (2 + 2 periods roundtrip) > and by jack_lsp -l (1 + 2 periods round trip). > This is for jackd2. > > jackd says: > > configuring for 44100Hz, period = 1024 frames (23.2 ms), buffer = 2 periods > ALSA: final selected sample format for capture: 32bit integer little-endian > ALSA: use 2 periods for capture > ALSA: final selected sample format for playback: 32bit integer little-endian > ALSA: use 2 periods for playback Capture latency in above message is a wrong. It was reported a while back: check jack-devel archive Dec 2010: http://old.nabble.com/jack-%281-and-2%29-latency-reporting-td30420262.html > However, jack_lsp -l says: > > system:capture_1 > port latency = 1024 frames > port playback latency = [ 0 0 ] frames > port capture latency = [ 1024 1024 ] frames > system:capture_2 > port latency = 1024 frames > port playback latency = [ 0 0 ] frames > port capture latency = [ 1024 1024 ] frames > system:playback_1 > port latency = 2048 frames > port playback latency = [ 2048 2048 ] frames > port capture latency = [ 0 0 ] frames > system:playback_2 > port latency = 2048 frames > port playback latency = [ 2048 2048 ] frames > port capture latency = [ 0 0 ] frames > > Is this inconistent, or is there some other explanation? with jack2, there's also the difference of sync (jackd --sync .. -d alsa ...) vs. async mode. The latter adds 1 period of output latency. see also: http://wiki.linuxaudio.org/wiki/jack_latency_tests >> If you masure it using jack_delay you will in most cases find a value >> that is a bit higher, this is due to delay in AD/DA converters etc. For >> some types of soundcard (e.g. USB) the real latency can be significantly >> higher than the nominal value. You can tell Jack about this using the >> -I and -O options. >> >> >> The extra delay when making a loop such as Ardour -> jconvolver -> Ardour >> is one period. > > Great to have these details available for unschooled > developers as myself! > > Regards, > > Joel > >> Ciao, >> >> -- >> FA _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
