[PD] latency, -frags, and -blocksize

jfm3 jfm3 at ouroboros-complex.org
Fri Jan 11 22:24:15 CET 2002

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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