[LAU] qjackctl and the hardware latency setting

[Robin Gareus]

On 01/01/2014 03:10 PM, Maciej (Matchek) Bliziński wrote:
> Hello list,
> 
> I've come across a problem where the hardware latency numbers entered into
> qjackctl setup window don't take effect. I wrote up the details here:
> 
> http://quinoa.blizinski.pl/~maciej/latency/calibration-problems.html

nice writeup.

Once the 'problem' is understood and fixed, it'd be great to make a "how
to calibrate latency" walk-trough out of it. You already have nice
"before and after" screenshots.

> The workaround was to start jackd from command line and pass the -I and -O
> options that way.

If it's jackdbus that you're using, maybe qjackctl does not configure it
properly; or maybe you're just missing 'use dbus' in qjackctl's config?!
-- but those are only guesses. One could look in the source or bug Rui :)

A few things that may help to track things down:
  'jack_control dp | grep latency'
prints the current configuration of jackdbus.

You can directly query the current port-latencies with 'jack_lsp -l'. It
lists the actual port-latencies as jack knows them, that includes
cycle-times, -I/-O configuration and latencies due to routing: eg.
effects with latencies, etc.

> It is possible (but not certain) that the problem was caused by qjackctl. I
> wrote a post on the qjackctl forum, but I'm not sure how much attention it
> gets.
> 
> http://www.rncbc.org/drupal/node/749
> 
> Since my setup is fairly common components: Ubuntu 13.10 with ardour, jackd
> and qjackctl installed from packages, it sounds like I shouldn't be the
> only person to experience this problem.
> 
> Has anyone else come across that?
> 
> Maciej
> 
>