[pvrusb2] pvrusb2-mci-20070114 radio support - stereo?

[Rick Macdonald]

Pantelis wrote:
>> The strangest thing. Last night when I booted the old laptop back to
>> Linux, I got stereo from pvrusb2. I then powered off the laptop and
>> PVR-USB2 and rebooted and the stereo still works. I've pasted the log
>> info below. This is a 2.6.15 kernel. No ivtv installed at all. I didn't
>> update v4l.
>>
>> Still no stereo on the original desktop. When I send Stereo/Mono to the
>> ctl_audio_mode, I think what I'm hearing is the tuner switching between
>> Stereo/Mono. The mono sound is cleaner and stronger because the
>> airy-hissy sound from the FM antenna is gone, but both are mono.
>>
>> I have two laptops, but the other one has a 2.4.x kernel so I can't try
>> that easily.
>>
>> Any suggestions? Should I yank out the internal PVR-150 as a test?
>>     
>
> So, it could be:
>
> * A regression in the cx25840 support module (it seems to have changed from 
> 2.6.15, I don 't know how much, especially if its defaults have changed)
> (unlikely)
>
> * A conflict because both your pvrusb2 24xxx and your PVR-150 (IIRC)
> use the cx25840 module
> (also unlikely)
>
> * A hardware limitation, because I very clearly remember this effect happening
> _in windows_ in some stations (the stereo sign would light up in wintv radio
> but the sound would actually be mono+hiss exactly as you report)
>
> * A configuration issue (IIRC the msp34xx module has a threshold parameter
> for signal strength after which it does stereo, I think  it was called 
> stereo_threshold - maybe cx25840 has something along the same lines), maybe 
> the problem is signal strength related?
>
>
> Given that this "fake stereo" problem is also present in windows (at least for
> 29xxx devices) I 'd suspect it is a hardware limitation and there is hardly
> any generic solution to it. If the cx25840 module allows you to adjust the
> stereo threshold maybe you could experiment a bit with that.
>   
Thanks for the reply. I don't quite understand the possibilities of a 
hardware limitation, because:

* On the P450 laptop running 2.6.15, I can get stereo FM from the 
PVR-USB2. I can yank the USB cord, plug it into the 2.6.18 desktop, and 
it's mono. I can move the cable back to the laptop, and it's still 
stereo. Therefore, the PVR-USB2 29032 device itself clearly handles the 
stereo.

Where could you see a hardware limitation being?

Some things I could try:

* remove the PVR-150 from the desktop
* upgrade the laptop to 2.6.18-3 to match the desktop
* I've been meaning to plug something into the PVR-USB2 Audio Input 
jacks. Would that be a useful test?

If the cx25840 module is different and applying a stereo threshold, that 
might make sense. However, wouldn't the threshold refuse to set the 
tuner to stereo? For it to allow the tuner to process the stereo signal 
but mix it to mono would be strange. If it's unintentional (ie a bug), 
then anything goes.

...RickM...