- Miller Puckette msp@ucsd.edu [2014-01-28 00:02]:
Probably that's so - but Pd should still be able to deal with the mismatch. OTOH, since Pd is built-in 64 blocksize, you wouldn't be able to reduce Pd's latency by reducing jack's blocksize below 64.
Allright, then I can live without going lower.
I'm not sure about this, but I believe that Pd running standalone (using ALSA driver) can achieve as low or perhaps slightly lower latency than Pd running under jack. This is only of interest if Pd's the only audio application you're running on that particular audio interface, however.
I can currently start pd using -alsa -rt -audiobuf 2 and get click-free performance, as long as I don't the classic "Select all.." and move things around in Tcl/Tk, which of course causes drop-outs. Haven't measured latency with that setup yet, but it sure sounds promising. Using the oss emulation of alsa works too, but slightly more clicks when moving objects on the canvas.
Made a latency test with pd's own latency testing patch /usr/local/lib/pd/doc/7.stuff/tools/latency.pd
-alsa -rt -audiobuf 2 -channels 18 on an HDSPe card with Multiface and a loopback analogue cable gives 6.5ms, which I consider great!
Interestingly Pd gives this latency value regardless of setting -audiobuf to values 1-6, which I suppose is because of rounding this value to something usable by the dsp part. Pd also reports on startup "...buffer_time 2902 us opened" "using mmap audio interface"
Now what is weird, is that I can't get clean audio under alsa with any values larger than -audiobuf 6. The sound is very distorted.
Using the -oss emulation and -rt, clean audio is available for values larger than -audiobuf 2 such as:
-audiobuf 3 with measured latency of 7.9ms (Pd choses blocksze 56) -audiobuf 5 with measured latency of 9.4ms (Pd choses blocksze 56) -audiobuf 6 with measured latency of 10.9ms (Pd choses blocksze 56) and so on.
Oh this is on a Debian system running kernel 3.2.0-4-rt-amd64
Nice that Pd can do so low latencies, but that's a strange thing about alsa though...
best, P
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