[LAU] New release of jack_delay

[S. Massy]

Thanks,
Builds and runs fine on Debian Wheezy AMD64. What latency would be
considered average? What numbers should one expect?

Cheers,
S.M.


On Mon, Apr 18, 2011 at 08:21:26PM +0000, Fons Adriaensen wrote:
> Hello all,
> 
> A new release of jack_delay is available at 
> <http://kokkinizita.linuxaudio.org/linuxaudio/downloads>
> 
> > From the README:
> 
> jack_delay 0.4.0  -  18/04/2011
> -------------------------------
> 
> Jack_delay can be used to measure the round-trip latency of a soundcard.
> To do this, start the program and connect like this:
> 
> jack_delay -> playback_port -> cable from soundcard output to input -> capture port -> jack_delay
> 
> Jack_delay generates a signal consisting of 13 sine waves, measures the
> phase difference between the input and output for each of these, and
> computes the delay from those phase differences. The algorithm used is
> one developed originally for satellite ranging -  that is measuring the
> distance between a satellite and a ground station.
> 
> With a good sound card jack_delay will measure the round-trip latency
> with an accuracy of around 1/1000 of a sample. The assumption is that
> the delay is more or less independent of frequency. The actual value
> displayed is the one for a frequency of 1/16 of the sample rate. The
> phase measurement for this frequency of course only provides a result
> in the range of 0..16 samples. The other frequencies are used to extend
> this interval to 4096 * 16 samples, more than a second at 48 kHz.
> This release should be much less sensitive to frequency-dependent delay
> than the previous ones. 
> 
> The following options are avaiable (use jack_delay -h to see them):
> 
> -O playback port   connect output to named port.
> -I capture port    connect input to named port.
> -E                 show excess latency instead of full latency.
> 
> Using -E requires -O and -I, as the the computation depends on
> the latency values reported by jack for the ports used.
> The excess latency is the measured value minus the expected one,
> taking into account any corrections set by jack's -I and -O options.
> That is, if you have the right values for these options, then the
> value displayed with -E will be at most +/- half a sample.
> 
> To determine the correct values for jack's -I and -O, set both
> of them to zero ('default' in qjackctl) and measure the latency
> using the -E option. Then set each of the -I and -O options to
> half the value displayed.
> 
> 
> Ciao,
> 
> -- 
> FA
> 
> 
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