Re: [linux-audio-user] My MIDI latency is crap

On Fri, 2006-05-05 at 12:32 -0500, Josh Lawrence wrote:
> On 5/5/06, Lee Revell <rlrevell@email-addr-hidden-job.com> wrote:
> > What is HZ set to in your kernel config?
>
> This is a new term to me. What does HZ mean, and how do I grep for it
> in my kernel config?

It's the kernel's internal tick rate and will determine the best
achievable MIDI output latency. The default changed from 1000 (1ms
ticks) to 250 (2.5 ms ticks) around 2.6.12, over the objections of the
linux audio community.

  grep HZ /boot/config-`uname -r`

or

  zgrep HZ /proc/config.gz

if you have those files. It should be 1000 for optimal MIDI latency.

I actually discussed this with Joachim from the MuSE team at LAC - we
need a way for applications that need a low latency capable kernel to
discover whether the kernel is good enough. One option would be to
simply make MuSE depend on a "known good for audio" kernel in the
package manager which is probably too aggressive, and not reliable
enough. A better solution would be to have a simple, user friendly app
that does a latency test and reports the results, and if a problem is
found would recommend that the user upgrade the kernel, change some
config options or file a bug report with their distro.

Unfortunately it's a tricky problem, as you can see there's not even a
distro independent way to check the kernel config.

Lee
Received on Sat May 6 04:15:03 2006