Pioneer DJ DDJ-SR2 sound degradation

[Geraldo]

Until we manage to engage implicit feedback sync for Pioneer gear I'm
afraid the clock will drift on DUPLEX mode.

I reread the Pioneer related source code and implicit feedback sync was
disabled because it gave Incompatible EP Setup messages. I should know, I
was a reporter on that regression.

Only those messages are fake. They arise because our ALSA code it's not
honoring .ep_attr on quirks-table.h specifically in regards to
USB_ENDPOINT_USAGE_IMPLICIT_FB.

In fact the new improved implicit feedback sync code inside pcm.c that sets
sync upon probe is failing to set implicit_fb to 1. I commented the
conditional for testing and I told endpoint_compatible to always return
true.

Voilà, JACK started in duplex mode without nasty Incompatible EP Setup
problems and supposedly with implicit feedback sync on. We are not setting
bits 5..7 of bmAttributes, at least that's what I get from the missing
Usage field in lsusb.

My JACK transport has been rolling for 17 minutes and if it goes for two
complete hours without distortion passing-thru vinyl on Mixxxx I'll provide
the list with a more elegant PATCH and not this gambiarra as we say on
Brazil.

Hopefully their will be implicit feedback sync for Pioneer :-)


On Thu, Mar 18, 2021 at 7:41 PM Geraldo <geraldogabriel at gmail.com> wrote:
>
> Hi everyone,
>
> I'm running stable kernel 5.11.6 together with my Pioneer DJ DDJ-SR2 and
JACK. Mixxx is running on top of JACK.
>
>
> After I start JACK I have about 40 minutes of good sound quality from the
inputs. After this period the sound will begin to degrade slowly until it
is almost pure distortion.
>
> The issue is gone if I restart the JACK server, no need to reboot the
hardware. The description I gave above sounds a lot like soundcard clock
drift (which happens to those using more than one soundcard. You know)
which motivates me to believe we missed a bug somewhere around the recent
changes introduced in implicit feedback sync for Pioneer devices
>
> Dyndbg shows nothing useful I guess. No xruns reported.
>
> I've recorded a 1KHz tone and after 50+ minutes the sound degradation
kicks in. Only problem is even after cutting and encoding to mp3 128kbps
it's still a 10 megabytes file. I suppose I could post it to Soundcloud or
Mixcloud if anyone is interested.
>
> Is anyone else experiencing these symptoms with Pioneer hardware? Note
that the sound degradation kicks in after about an hour, more or less, and
it's for the inputs only. Outputs continue to operate fine without the need
to restart the JACK server every hour.
>
> Thanks everybody,
> Geraldo