On Fri, 2013-12-20 at 15:04 +0100, Clemens Ladisch wrote: > Ralf Mardorf wrote: > > I never tested it myself, however, I remember that it often is mentioned > > not to use -n >2. Is there a reason to avoid -n >2 or is t juts a myth? > > The buffer size is the product of the period size (-p) and the number of > periods (-n). A larger buffer size increases latency, but reduces the > risk of underruns. A smaller period size _slightly_ increases CPU usage > because of the overhead needed for handling a period. > > Therefore, when optimizing for low latency, one typcially uses two > periods and makes -p as small as possible. > > With USB devices, the period boundaries (where interrupts are supposed > to happen) are not necessarily coincident with the USB frame boundaries > (where interrupts actually happen). This results in delays (jitter) of > up to 1 ms in the timing of period interrupts; with very small buffer > sizes, this increases the risk of underruns greatly. So if, e.g., the > machine is not able to handle "-p 64 -n 2" reliably, increasing the > number of periods to 3 results in lower latency (3*64=192) than > increasing the period size (2*128=256). (Using "-p 96 -n 2" would have > the same latency, but works only if that particular Jack version allows > period sizes that are not a power of two.) Thank you too. Jeremy already posted a link to a thread where _you_ explained it :) (less detailed than now). Résumé: As Fons pointed out, the sound quality isn't affected by the -n size. I assume even sync between audio and MIDI, between several devices isn't affected by the -n size, but just some prosumer USB devices could cause less good sync between audio and MIDI, irrelevant for this thread. Regards, Ralf _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
