[linux-audio-user] jackd, zynaddsubfx and iiwusynth

Jack O'Quin joq at io.com
Mon Mar 3 23:34:01 EST 2003

Levi Burton <donburton at sbcglobal.net> writes:

> I looked at jackd options, maybe someone could explain what they do for me:
>  1.  -p,--period <n>     frames per period (default: 1024)
>  2.  -n,--nperiods <n>   number of periods in hardware buffer (default: 2)
>  3.  -H,--hwmon          use hardware monitoring, if available (default: no)
>  4.  -s,--softmode       soft-mode, no xrun handling (default: off)

I'll try.  Someone please correct me if I get any of this wrong.

  -p sets the number of frames between JACK process() calls.  This
  must be a power of two (IIRC).

  -n is the number of such periods in the buffer.  P*N*4 is the size
  of the JACK buffer in bytes.  Larger buffers yield higher latency,
  but fewer xruns.

If you need low latency, set -p and -n as low as you can without xrun
problems.  Reasonably well-tuned current-generation systems with a
decent sound card and JACK running --realtime on a low-latency kernel
can handle -p 128 -n 3 reliably.  Some can do better.  Tuning a system
for low latency is challenging.

If you don't need low latency, set -p and -n higher to insulate
yourself from xruns.

  -H tells JACK that your sound card provides capture input

  -s tells JACK's ignore xruns reported by the ALSA driver.  This
  makes JACK less likely to disconnect ports when running without

  Jack O'Quin
  Austin, Texas, USA

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