[pvrusb2] Occasional audio issue with recordings

[Mike Isely]

Jan:

This might be something involving the cx25840 chip-level driver which is 
part of V4L.  That corresponds to the part of the device which processes 
audio.  It's also the point in the hardware where line-in analog video 
meets up with demodulated audio - so if you are seeing a problem with 
line-in but not an RF source then it's either got to be this chip or 
something in front of it.  There may be an ADC upstream of that part for 
the line-in for the HVR1950 but it's been so long that I don't 
specifically recall.  In any case, the pvrusb2 driver doesn't do the 
actual "processing"; it just sets up the dataflows via the various 
chip-level drivers.

With that knowledge, see if unloading / reloading the cx25840 module 
might affect the issue.  (And that should actually work right now.)  
Also, you might want to see if there's a different firmware image 
floating around for that part.

  -Mike


On Mon, 4 Nov 2019, Jan Ceuleers wrote:

> Dear pvrusb2 list,
> 
> Ever so often one of my HVR1950 tuners, which records from a
> directly-connected set-top box, gets into a state where audio is damaged
> such that it cannot be played using either MythTV nor MPlayer. Video is
> fine, but audio is damaged.
> 
> A sample can be found here:
> 
> https://gofile.io/?c=DQSKjQ
> 
> Judging by the loud click when starting playback, along with the
> occasional crackling that can be heard it sounds as if a large DC offset
> has been added to the audio signal such that the audio decoder's output
> is saturated. But that's just an assumption.
> 
> The only way to recover is to reboot -- when the driver once again
> becomes removable I'm sure an rmmod/modprobe cycle will be enough. That
> is: it is not necessary also to power cycle the tuner itself.
> 
> I have already excluded the possibility of these symptoms being caused
> by an iffy power supply.
> 
> Any hints would be gratefully received.
> 
> Best regards, Jan
> 
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-- 

Mike Isely
isely @ isely (dot) net
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