[Jack-Devel] Linking apps together from script

Chris Caudle chris at chriscaudle.org
Tue Jul 26 22:29:54 CEST 2016

On Tue, July 26, 2016 1:16 pm, james-rpf wrote:
> I'm trying to get receive audio data from a USB software defined radio and
> pipe it through jack to alsa out and also to another app dl-fldigi.

Are you using alsa_out because you need sample rate conversion?  Why are
you not sending to the ALSA hardware device directly?  Or do you mean you
connect to the output of your ALSA hardware, and not that you are using
the "alsa_out" resampling jack client?

> Secondly I have some audio issues, there are fractional pauses every so
> often which make the audio had to decode, is there anything about piping
> through jack that could cause this, on something which might mitigate it?

Look for underrun/overrun messages in jack (probably displayed as "xrun"
If you have xrun problems you can try increasing the number of frames per
period, and when using USB the recommendation is typically to use 3
periods per buffer (-p and -n arguments to jackd respectively).

If all else fails you can switch to a kernel with real-time extensions
(-RT patch series).  I don't think you mentioned what kernel you are
using, before switching completely to the -RT variant you could also try a
kernel compiled with the low latency configuration (shown as voluntary
preemption in the kernel config options, will show as PREEMPT in the
kernel config file).  Often a PREEMPT kernel with large number of frames
per period will work well enough that you don't need the PREEMPT-RT kernel

Chris Caudle

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