[alsa-devel] Hercules P32 DJ: severe sound distortion during MIDI transfers

[Guido Trentalancia]

Hello Takashi.

I have carried out the test that you proposed...

My reply follows your quoted text.

On Fri, 22/03/2019 at 11.12 +0100, Takashi Iwai wrote:
> On Fri, 22 Mar 2019 11:04:01 +0100,
> Guido Trentalancia wrote:
> > 
> > Hello Takashi,
> > 
> > I am using the latest version of everything, including kernel and
> > ALSA
> > userspace library / tools.
> > 
> > The other user has exactly the same hardware and has tested same
> > firmware
> > (both 1.36 and latest 1.46), but with Fedora 29 and it is working.
> > 
> > Perhaps Fedora 29 has a different version of the ALSA library, I
> > will find
> > out, try to downgrade, test again and report back.
> 
> Yes, that'd be really helpful.  If aligning the software doesn't fix
> the issue, it's either because of the hardware or the difference of
> usage patterns.

I have tested exactly the same ALSA userspace library and plugins
distributed by Fedora 29 and it does NOT work !

As already explained, the usage pattern is exactly the same between me
and the user which is not experiencing this severe problem.

Also, the hardware is the same: Hercules P32 DJ (with exactly the same
firmware version 1.46 which is the latest).

So, the conclusion is that it must be a kernel bug ! I was expecting
this, as already pointed out in previous messages.

Can you please help me fix this bug since you wrote the driver and/or
are maintaining it ?

Thanks,

Guido

> thanks,
> 
> Takashi
> 
> > 
> > Guido
> > 
> > Il 22 marzo 2019 10:53:11 CET, Takashi Iwai <tiwai at suse.de> ha
> > scritto:
> > 
> >     On Fri, 22 Mar 2019 10:17:17 +0100,
> >     Guido Trentalancia wrote:
> >          
> >          It cannot be a firmware bug, as you say, because:
> >          
> >          - it does NOT happen on Windows!
> >     
> >     It doesn't mean that the device behaves correctly as
> > advertised.
> >     
> >          - it does NOT even always happen on Linux: other users
> > (with different kernel
> >          / ALSA library) are not experiencing the same problem;
> >          - it happens with several firmware versions, including the
> > latest one (1.36
> >          and 1.46).
> >          
> >          So it is either a bug in ALSA kernel driver, USB sound
> > driver (more likely) or
> >          ALSA library.
> >          
> >          Now, you are in charge of the USB sound driver, can you
> > please double check??
> >     
> >     If it doesn't happen for other users with the very same device,
> > you'd
> >     need to identify what's the difference between your case and
> > others.
> >     For example, if the difference of alsa-lib matters, you can try
> > the
> >     very same condition.
> >     
> >     This kind of bug can't be easily debugged without the actual
> >     hardware, unfortunately.
> > 
> >     Takashi
> > 
> >          Regards,
> >          
> >          Guido
> >          
> >          Il 22 marzo 2019 09:55:52 CET, Takashi Iwai <tiwai at suse.de
> > > ha scritto:
> >          
> >              On Thu, 21 Mar 2019 23:27:46 +0100,
> >              Guido Trentalancia wrote:
> >                   
> >                   I wonder if this might be due to a bug in the
> > "USB Audio Driver for Alsa"?
> >                   
> >                   https://git.kernel.org/pub/scm/linux/kernel/git/t
> > orvalds/linux.git/tree/sound/usb
> >                   
> >                   https://git.kernel.org/pub/scm/linux/kernel/git/t
> > iwai/sound.git/tree/sound/usb
> >              
> >              More likely a buggy firmware of your USB audio device
> > :)
> >              
> >               From the driver implementation POV, both audio and
> > MIDI devices are
> >              handled by individual endpoints, hence they shouldn't
> > conflict.
> >              
> >              Or another possibility would be some USB host side
> > issue like the
> >              bandwidth.  But
> >              it's a MIDI stream that is very low data rate, so this
> >              sounds also unlikely...
> >          
> >              thanks,
> >              
> >              Takashi
> >          
> >                   Guido
> >                   
> >                       On the 20th of March 2019 at 21.47 Guido
> >         Trentalancia
> >                       <guido at trentalancia.com wrote:
> >                      
> >                       Hello.
> >                      
> >                       I am hitting a very serious bug (ALSA kernel
> > driver or ALSA library)
> >                       when using the Hercules P32 DJ audio
> > interface.
> >                      
> >                       The sound is severely distorted during MIDI
> > transfers.
> >                      
> >                       To reproduce:
> >                      
> >                         + start playing something in a first
> > console:
> >                      
> >                       console1# AUDIODEV=hw:2,0 play audio.wav
> >                      
> >                         + the audio plays fine
> >                          
> >                         + now start "amidi" in a second console
> > while the above track is still
> >                           playing
> >                          
> >                       console2#
> >                  amidi -p hw:2,0,0 -d
> >                      
> >                         + the sound is now severely distorted
> > (basically noise, with some
> >         hard-
> >                           to-distinguish features resembling the
> > original track) until "amidi"
> >                           is
> >                           interrupted !
> >                      
> >