[pvrusb2] audio pops and cracks in the recordings

[Mike Isely]

On Sun, 21 Jan 2007, devsk wrote:

> I haven't tried the device in windows. Do I really have to? Do you 
> think its a device specific problem?

Yes, I think it is very possible.  I can imagine that bad a filter cap 
or some kind of failing transistor might produce this sort of 
distortion.  What I find most remarkable is that the example you sent 
has the pops happening in sync with the energy spikes in the audio 
track.  It really does sound like what you'd get playing audio through a 
damaged speaker cone.  That to me sounds like a hardware issue.  
Hardware isn't infallible; I was fooled for 6 weeks straight about a 
year ago chasing a software ghost that turned out to be defective 
hardware (scan the mailing list from about Dec 2005 and look for stuff 
about B&W video if you want to see).  The best way to prove (or 
disprove) this sort of thing is to swap out the software and see if the 
problem still happens.  In other words, run it under Windows and see if 
the audio is ok or not.


> 
> do you think reducing bass (from default 0 value) will help, maybe? It 
> sounded exactly like you described. Imagine listening to whole 2 hour 
> Yanni live with those pops here and there, after a while I got sick of 
> it, although the music was awesome!.

Well it's a nice idea to reduce the bass, except it's entirely possible 
that the bass control is not implemented in the hardware.  The msp3400 
chip in the 29xxx devices has a datasheet that allows for tone controls, 
and in fact the Linux msp3400 driver implements these.  For this reason 
the pvrusb2 driver makes those controls available.  However it depends 
on the exact msp3400 variant being used and I've seen examples where the 
tone control circuitry just isn't there in the chip.  (Not sure off the 
top of my head about 24xxx devices which use a cx25840 chip for audio.)


> 
> The settings were at their default when the sample was taken: cat'ed 
> the values I changed, before taking sample, to make sure. I am not 
> sure how to go about debugging this thing.

OK.

I think your next best step is to try it under Windows.  Some advice 
(from a hard lesson I just learned today): If you are installing the 
software under Windows 2000 (as opposed to XP), make sure you have your 
Direct-X installation up to date.  The driver CD from Hauppauge includes 
this, but if you just download the drivers from the web site and install 
that way, then you'll miss the undocumented Direct-X requirement.  I 
pulled my hair out for a full day today trying to figure that one out.  
Anyway, I think you definitely need to run the device under Windows and 
test the audio there.  Sorry :-(

  -Mike

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