[LAU] [LAD] Document on using Jack Apps

Arvind Venkatasubramanian mdu.arvind at gmail.com
Sun Aug 1 18:37:09 UTC 2010

Thanks to Julien and Rui Capela.  Being a musician and engineer, this seems
to be a great place to land in and learn new stuff in this world
of Linux audio.  Currently, I am still not able to find document that I need
to solve 2 existing problems:

*Question on using JDelay:*

I have only one web source that has some details about using this tool:

http://www.kokkinizita.net/linuxaudio/   and this reads:  "It uses a phase
measurements on a set of tones to measure the delay from the output to the

How do I use these phase measurements and how do I pass in these tones?  Are
they special tones?  What kind of oscillator do I need to use to generate
these special tones?  How do I pass in an audio tick or click?  How do I do
other settings?

$ jack_delay -h --help does not show me the help menu

*Question on using QJACKctl:*

I was able to create some basic setting, load and read latency that gets
printed on the terminal.  But what do the parameters on the setting tab of
console pop up mean?  No soft mode, monitor, priority, time out etc and the
options tab.  How do I use these options and tine tune them in order to set
the minimum feasible latency for the application that I intend to develop?
 Above all, if the drop down menu options does not allow me to choose lower
sampling rates, what command do I use on the CLI to do the setting.  Or Do I
need to edit QJACKctl's .conf file to set lower sampling rates manually.

My Intel sound card supports sampling rates of 8kHz and 16 kHz.  I confirmed
this by looking into Audacity device ID setting.  I know that I am asking
some basic stuff but my problem is that I do not find the right
documentation for solving my problems.

Your reply in this regard will be greatly appreciated.

Kind regards,
Arvind V

On Sat, Jul 31, 2010 at 7:01 PM, Rui Nuno Capela <rncbc at rncbc.org> wrote:

> On 07/31/2010 11:23 PM, Arvind Venkatasubramanian wrote:
> > Hello:
> >
> > I am very much new to Linux and Linux audio.  I am trying to measure
> > audio IO latency for my system.
> > Jdelay seems to be the right tool but when I run it on the terminal, I
> > am getting message "Signal below threshold..." which probably might be
> > because Jack is trying to capture audio and ends up getting the low
> > noise floor because I do not have meaningful signal source connected.
> >  But then I tried to patch the this App to the qJACKctl app but the
> > settings console is not straight forward to interpret. as it involved
> > many parameters.
> >
> > I guess there are # of frames per period that may eventually be used
> > to calculate the target latency but *is there a step-by step document
> > description for Jdelay and any other JACK tools and also using JACK
> > audio server in an effective manner*?  Also, qJACKctl console does not
> > offer options for very low sampling rates like 8 KHz.  With ALSA, this
> > should be possible but may be this particular tool does not support it.
> >  Can anyone help here?
> >
> re. qjackctl settings you can actually write whatever sample-rate you
> want. you're not limited to the options given in the drop-down list.
> however, that doesn't mean that the soundcard will stick to it, ever :)
> cheers
> --
> rncbc aka Rui Nuno Capela
> rncbc at rncbc.org
> _______________________________________________
> Linux-audio-dev mailing list
> Linux-audio-dev at lists.linuxaudio.org
> http://lists.linuxaudio.org/listinfo/linux-audio-dev
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