[pvrusb2] audio pops and cracks in the recordings

[Mike Isely]

On Mon, 22 Jan 2007, devsk wrote:

> After 1.5 hours, I have booted back into linux and I can immd. see that I don't have to wait for even 45 seconds on pbs to make it produce pops.
> 
> I notice this occurring in the mythtv logs pretty often, but its not there for every pop.
> 
> 2007-01-22 19:16:34.386 WriteAudio: buffer underrun
> 2007-01-22 19:16:34.536 NVP: prebuffering pause
> 
> -devsk
> 
> ----- Original Message ----
> From: devsk <funtoos at yahoo.com>
> To: Communications nexus for pvrusb2 driver <pvrusb2 at isely.net>
> Sent: Monday, January 22, 2007 6:12:44 PM
> Subject: Re: [pvrusb2] audio pops and cracks in the recordings
> 
> > Anyway, I think you definitely need to run the device under Windows and test the audio there.
> 
> ok, I have been watching the pbs channel for more than 45 minutes in windows xp pro and I can't hear even a single pop so far. The channel has played much more intense music compared to the clip I posted earlier. So, it doesn't look like the device problem. I have tried various channels (CMT has lot of guitar and no pops there) and no pops anywhere so far. Where do we go from here?
> 
> I will stay in windows xp until I hear from you, if you want me to do some troubleshooting in windows. And also to see if with time it heats up or something and starts popping.....:)
> 
> -devsk

Sorry, on Mondays I've away from the net for pretty much the entire 
night.

I don't have any obvious solutions here.  So far you're still the only 
person to tell me of problems like this and I can't really seem to 
reproduce the problem here (but read on).

Given that XP is OK, then the hardware has to be fine and we're left 
looking at the software.  So what's difference?  The pvrusb2 driver is 
clearly the same.  The kernel version is different.  I'm still running 
2.6.18.1 here.  I did test against 2.6.19-rc2 (I think) briefly a while 
back and don't remember encountering any kind of problem like this.  I 
can try to update my kernel here and see if the problem happens.

Is there anyone else here with devsk's setup and is or is not seeing 
this problem?  The key to this problem is to figure out what is 
different.

Now with that said, I *did* manage to do one thing here that seemed to 
produce a similar symptom.  On a 29xxx device I had accidentally left 
the coax plugged into the TV F-connector while trying to listen to the 
radio.  The result?  I got the audio but it was full of cracks and pops, 
similar in pattern to what you got.  But this was in radio mode on a 
29xxx device, which is different than your situation.  I tried the same 
experiment on a 24xxx device but the result was total static that time.

Thinking further, I can see how a weak FM-modulated signal could do 
something like this - bursts of audio energy might displace the carrier 
faster than the tuner can track the weak signal and thus it pops.  That 
might suggest something is misprogramming the tda9887 on your device 
causing the audio signal to be too weak.  I think there have been cases 
like that on other (non-pvrusb2) hardware, but I'm not really sure.

The best strategy here may be to compare environments and try to match 
them up.  I will try out a 2.6.19.2 environment and see what happens.  
But it may be a few days yet before I can try that experiment.  You 
might want to try kernel 2.6.18.1 and see if the cracking and popping 
still happens.  I'm not hopeful that this is your problem, but we seem 
to be running out of options.

You might also want to try building the latest v4l-dvb repository and 
installing that in your kernel.  That will give you the absolute latest 
versions of all the support modules, so if the problem has been recently 
fixed then we don't have to keep chasing this.

  -Mike

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