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

[Christian Affolter]

On 31.01.2018 15:20, Kjetil Matheussen wrote:
> On Wed, Jan 31, 2018 at 3:08 PM, Christian Affolter
> <c.affolter at purplehaze.ch <mailto:c.affolter at purplehaze.ch>> wrote:
> 
>     On 31.01.2018 11:42, Kjetil Matheussen wrote:
>     > On Wed, Jan 31, 2018 at 11:29 AM, Christian Affolter
>     > <c.affolter at purplehaze.ch <mailto:c.affolter at purplehaze.ch>
>     <mailto:c.affolter at purplehaze.ch <mailto:c.affolter at purplehaze.ch>>>
>     wrote:
>     >
>     >
>     >     Yes, it's a proprietary driver and I don't have access to the source
>     >     code. I could contact the vendor and ask if they observed the same or a
>     >     similar issue already.
>     >     However, I'm wondering what arecord and jackd-dummy/alsa_in are doing
>     >     different compared to jackd-alsa.
>     >
>     >
>     > Sorry if this is not relevant (I'm not quite following what's
>     > happening), but could
>     > it be that the difference can be explained by different alsa paremeters set
>     > by arecord and jack? Have you tried to run "arecord -L" and find the most
>     > low-level device to record from (which jack probably uses).
>     >
>     > For instance by running something like "arecord -D iec958:CARD=M2496,DEV=0" 
>     > (my soundcard).
>     >
>     > If that is the case, then it's probably the default alsa device that
>     > does something magic
>     > when accessing a more low-level device.
> 
>     I ran both, arecord and jackd with hw:0 initially. I re-ran the capture
>     again with "arecord -D default:CARD=Axia ...", which didn't make any
>     difference (the recording sounds correct).
> 
>     For the record, here is the ALSA capture PCM and device list:
> 
> 
> Maybe jack will work if you give it the same parameters that arecord
> uses. I.e. compare
> the content of  /proc/asound/card0/pcm0p/sub0/hw_params (or a similarly
> named file)
> when running arecord and when running jack.
> 
> Also, maybe it works to record in jack if you change audio from "duplex"
> to "capture only".

BINGO and thank you so much for this pointer!

If I start jackd in capture-only mode with only two channels, the
capturing finally works as expected:

jackd -d alsa -d hw:0 -C -i 2

Interestingly, the different period size of 4096 vs. 1024 doesn't seems
to have any impact (I first tried to run with -p 4096 as well).

Below are the HW parameters of the ALSA device, during different states.

# hw_params during arecord
cat /proc/asound/card0/pcm0c/sub0/hw_params

access: RW_INTERLEAVED
format: S32_LE
subformat: STD
channels: 2
rate: 48000 (48000/1)
period_size: 4096
buffer_size: 16384


# hw_params during jackd -d alsa -d hw:0
# jackd -d alsa
cat /proc/asound/card0/pcm0c/sub0/hw_params

access: MMAP_INTERLEAVED
format: S32_LE
subformat: STD
channels: 8
rate: 48000 (48000/1)
period_size: 1024
buffer_size: 2048


# hw_params during jackd -d alsa -d hw:0 -C -i 2
cat /proc/asound/card0/pcm0c/sub0/hw_params

access: MMAP_INTERLEAVED
format: S32_LE
subformat: STD
channels: 2
rate: 48000 (48000/1)
period_size: 1024
buffer_size: 2048



Thank you everyone for your valuable help!
Chris