[PD] latency, -frags, and -blocksize
mpuckett at man104-1.ucsd.edu
Sat Jan 12 06:28:01 CET 2002
Hi, one small comment... "blocksize" only controls the I/O block size,
not the DSP block size, which is always 64. Control latency is always
64 samples but timing accuracy of I/O for control depends on I/O block
size, since timing is all derived from ADC and/or DAC transfers which are
made each I/O block.
On Fri, Jan 11, 2002 at 04:24:15PM -0500, jfm3 wrote:
> Thanks for your reply.
> I set -noadc (since I don't really use the audio in anyway, just
> prerecorded material). The lowest I could get it was
> -frags 8 -blocksize 64
> The default is 12 and 64. Then, at that point, removing -noadc made no
> I can also run
> -frags 4 -blocksize 128
> -frags 2 -blocksize 256
> That's about as far as she goes.
> I don't see anything simple in the code that would suggest I'm doing
> -noadc wrong. How did you get it to happen?
> Andrew (Andy) W. Schmeder wrote:
> > blocksize is the dsp vector size, also controlls the temporal resolution
> > of messages... ie. your midi messages can only be processed on block
> > boundaries. Midi having a clock with 1 ms resolution means you want a
> > small blocksize to match. bs = 64 => ~1.4 ms resolution which is
> > decent.
> > frags is latency... i.e. the number of blocks of lag. IMHO its better
> > to have more frags than a large blocksize.
> >>My laptop has a i8x0 sound card built in that I'm using. For MIDI I use
> >>the serial port and a MIDIator 124W. I have lowlatency patches applied
> >>to a 2.4.18 kernel, and am using ALSA 9b10. Thanks for any and all help.
> > I have an i8x0 sound card in a laptop as well (tosh portege 3440ct) and
> > with lowlat patch and alsa 0.9b. Basically the card sucks. In full
> > duplex its impossible to to run with less than 15 ms latency... i.e.
> > blocksize 64, 10 frags. However if I disable the dac or the adc (-nodac
> > or -noadc) then I can get it down to 1.5-3 ms latency.... but usually
> > that's not desirable. I'm certain its a fundamental limitation of the
> > card. Someday we will get a decent USB or pcmcia sound solution for
> > linux and everyone with a laptop will rejoice.
> > andy
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