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

Michael Krufky mkrufky at linuxtv.org
Fri Jan 19 14:59:44 CST 2007

Pantelis wrote:
>>> This could very well be a bug in the V4L chip-level driver for the
>>> demodulator.  Or it could be that the FM radio simply doesn't work in
>>> stereo (which would be rather astounding).  There are a few other leads
>>> to chase here.  I'm going to try this same experiment under Windows.
>>> If someone would like to try that first, I'd welcome hearing about the
>>> result. 
> [ snip ]
>> OK, I installed the USB2 onto a WinXP laptop. The WinTV Radio program is
>> stereo. A red STEREO 'led' lights up, and there's a MONO toggle button
>> that does what it says. My original package just says "FM radio
>> receiver". It doesn't mention stereo (but their web site does).
> I can confirm that under windows the WinTV Radio program does stereo
> and even autodetects which stations broadcast stereo vs mono (not
> everybody broadcasts stereo here). Unfortunately I cannot test that under
> linux since my test system does not have any speakers and I 'm testing
> with a *single* headphone (the one attached to a close-talk mic). So no
> chance of testing whether it sounds like stereo. (Otherwise I would probably 
> have caught this earlier). This is for a model 29034.
> So, it is either a bug in the demodulator, or we are missing some bit
> of (initialization?) code or doing something different. In any case, this 
> needs more investigation.

I could be wrong, but, to my understanding, the determination of stereo vs mono
lies 100% in the programming of the tda9887 analog IF demodulator.

The tda9887 is handled by tuner.ko, and it should already know how to handle FM
Stereo.  I haven't looked closely at the tuner handling code within pvrusb2, but
perhaps the tuner handling has been abstracted such that the tuner.ko module
isnt getting full control of tuning commands?  just a thought... Mike Isely will
know better on how to check about my theory, here.

Another theory, although unlikely, is that the tuner and tda988x is already
being programmed correctly, but the mpeg encoder isn't encoding the mpeg audio
in stereo mode.  This *is* possible, although unlikely due to the fact that we
know that the stereo stream is being encoded properly in television mode.

Anyway, just a thought... I could be totally wrong here.  Mike, what do you think?
Michael Krufky

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