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

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Subject: Re: [linux-audio-user] jackd, zynaddsubfx and iiwusynth
From: Jack O'Quin (joq_AT_io.com)
Date: Tue Mar 04 2003 - 06:25:19 EET


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
  monitoring.

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

-- 
  Jack O'Quin
  Austin, Texas, USA


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