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

Pantelis pakt223 at freemail.gr
Thu Jan 25 01:59:55 CST 2007

> 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)

* 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.


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