Re: Hercules P32 DJ: severe sound distortion during MIDI transfers

[Takashi Iwai <tiwai@suse.de>]

On Fri, 22 Mar 2019 14:44:48 +0100,
Guido Trentalancia wrote:
> 
> 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.

Did you test the very same kernel, too?  Without that confirmation, no
one can conclude that at all...

If the kernel makes difference, you can try identify which kernel
version starts showing the problem, and at best, do git bisection.


thanks,

Takashi


> 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@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@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@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 !
> > >                      
> > > 
>