On 23.11.20 15:18, Will Godfrey wrote: > On Mon, 23 Nov 2020 14:55:10 +0100 > David Kastrup <dak@xxxxxxx> wrote: > >> David Kastrup <dak@xxxxxxx> writes: > <some snippage> >> Question: is there a reason that you are going with buffer sizes of >> 3*2^n rather than 2^n? I've not actually tried what Jamulus does in >> that situation (but will do) but it seems a bit strange to me. Does it >> have some inherent advantage? > > This puzzled me too. I was under the impression that the reason for using powers > of 2 was that buffering code was more efficient. Presumably that would give the > best latency figures. > Here is data for the Focusrite Scarlett solo for all period sizes P from 16 to 240 frames in steps of 16 frames: P frames ms 16 114.847 2.393 32 176.847 3.684 48 232.847 4.851 64 294.847 6.143 80 368.847 7.684 96 424.847 8.851 112 498.847 10.393 128 566.847 11.809 144 616.847 12.851 160 684.847 14.268 176 752.847 15.684 192 802.847 16.726 208 876.847 18.268 240 1000.847 20.851 This is almost perfectly 4*P+48, for all P. I can also start it with P = 37 (an arbitrary prime number), so it looks that there is no limitation on the period size. Also for such odd numbers it remains 4*P+48 (the exact delay varies a bit between jack starts, which is normal for USB devices). This is jackd2 - I don't know if jackd1 behaves differently (although both would use the underlying ALSA layer). I started jack with jackd --sync -P 90 -d alsa -d hw:$CARD -r $RATE -p $PERIODSIZE CARD=USB RATE=48000 At 44.1 kHz it is more like 4*P+70 samples, although there is more fluctuation. Best, Giso _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx https://lists.linuxaudio.org/listinfo/linux-audio-user
