[Jack-Devel] Capture problems with jack2 on Axia-Alsa device

[Thomas Brand]

On Tue, January 30, 2018 20:35, Chris Caudle wrote:
> On Tue, January 30, 2018 12:46 pm, Christian Affolter wrote:
>
>> What I also observed is the fact, that capturing 10 seconds
>> (jack_capture -d 10 ...) directly from the "-d alsa" jackd takes around
>> 40 seconds (real 0m40.457s) vs. 10 seconds (as one would expect) with
>> the "-d dummy" jackd (real 0m10.339s)
>
> That is very strange, the test-arecord.wav and test-jack_capture.wav
> files are the same size, the file captured with jack is not 4 times
> larger.
>

indeed, very strange

> Does that CentOS machine have any attached audio hardware?  If so you
> could use the alsa_out plugin to play the captured audio, for example
> through a USB audio interface, and if that audio path is OK maybe just
> jack_rec or jack_capture is causing the problem.  I'm not sure what other
>  capture programs can run headless and capture from jack, NAMA perhaps?
> Actually I just checked and NAMA uses ecasound as the backend, just use
> ecasound directly, it has jack support.
>
> How did you get the file to play back at 12kHz?  Could you tell if it was
>  really distorted like the capture was mis-packing the original data,
> taking a 32 bit input word, putting just 16 bits of that into the first
> half of a 32 bit word...that only accounts for 2x time, not 4x, and is
> really a stretch, I don't see how an error that egregious could slip
> through jack or jack_capture.  Very strange.
>
i used a hand-crafted non-released player that can do it. it's just
playing the 48k file as if it would be 12k. any resampler could do it. it
was not distorted but i could hear the 's' is degraded. it could be 7.5
bit or something. very strange.