On Sun, May 30, 2010 at 11:02 AM, Grant <emailgrant@xxxxxxxxx> wrote: >> ALSA uses the sound card interrupt for timing. The hrtimer is used only >> for MIDI playback and for sound cards without interrupts, such as the >> SuperH, i.MX, PC Speaker, and dummy devices. > > Are you sure? CONFIG_SND_HRTIMER says: > > "ALSA uses the hrtimer as a precise timing source. The ALSA sequencer > code also can use this timing source." > > Would ALSA use the sound card interrupt for timing with my USB DAC? I too would like to better understand these statements and the benefits, if any, provided by loading snd-hrtimer. For example, if snd-pcm wasn't dependent on snd_timer, why this dependency from lsmod?:: > snd_timer 19840 5 snd_seq,snd_hrtimer,snd_pcm What kinds of timing info is snd_pcm deriving from snd_timer?? What are the benefits of using HRtimer versus system timer with ALSA? Which results in best performance (latency and drummer-accurate MIDI timing). Which uses least system resources? On Fri, May 28, 2010 at 12:11 PM, Paul Davis <paul@xxxxxxxxxxxxxxxxxxxxx> wrote: >> Does setting "--clocksource" only affect MIDI, or also Audio? >> ( http://old.nabble.com/Re:-Quality-of-sound-on-RHEL-6.0-beta-and-Fedora-13-p28587664.html ) > > neither. Then what is the purpose of the --clocksource flag, and what are the advantages/disadvantages of the different settings: "c(ycle) | h(pet) | s(ystem)"?? In a different thread you mention, regarding jackd's use of snd-seq: > the timing behaviour of the two -X options (seq and raw) are not very good. some might be sufficiently uncharitable as to call them unusable". Would using snd-hrtimer with snd-seq change this assessment? I haven't done any precise measurements myself, but I didn't hear anything sound terribly "off" w/r/t my usage of ALSA midi through qjackctl/jackd ( "/usr/bin/jackd -dalsa -dhw:M66 -r44100 -p256 -n2 -Xseq -zs -H -M"). Certainly not "unusable" just using MIDI alone. Is this issue related to timing of MIDI versus audio, or MIDI timing itself causing the music to sound different than the musician intended? Thanks for all the helpful advice, Niels http://nielsmayer.com PS: To get snd-hrtimer at boot in Fedora: http://old.nabble.com/-etc-modprobe.d-dist-alsa.conf-patch-to-boot-with-high-res-timer-for-ALSA-seq.-to28718916.html _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
