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

[devsk]

I have an observation to make on a 24xxx device (PVR USB2):

# cd /sys/class/pvrusb2/sn-*

# cat ctl_audio_mode/cur_val
Stereo

# cat ctl_mpeg_audio_mode/cur_val
Stereo

# cat ctl_audio_modes_present/cur_val
Mono

# cat ctl_audio_modes_present/bit_val
Mono
Stereo
Lang2
Lang1

# echo "Stereo" > ctl_audio_modes_present/cur_val
-su: ctl_audio_modes_present/cur_val: Permission denied

So, if the audio mode present and settable is "Mono", how is the overall audio stereo? Is the value of ctl_audio_modes_present/cur_val decided by the signal strength? Signal strength should be same between whether I am booted in linux or windows, right?

I did the 'mplayer -vo null -ao alsa -af pan=2:1:1:-1:-1 /dev/radio0' experiment and I hear "squeaking noises like from a tape bewing in extremely fast forwind most of the time."

I have had pops/cracks in the sound on mpeg2 stream on /dev/video0 which I worked around by setting bass and treble, which makes it sound sort of flat. Even otherwise, it hardly sounds like anything remotely close to how it sounds in windows (sorry, that comparison keeps coming). I wish I could help more to find the exact cause of the audio problems, but now you have another data point and tester....;-)

-devsk

----- Original Message ----
From: Pantelis <pakt223 at freemail.gr>
To: Communications nexus for pvrusb2 driver <pvrusb2 at isely.net>
Sent: Saturday, January 27, 2007 5:56:50 AM
Subject: Re: [pvrusb2] pvrusb2-mci-20070114 radio support - stereo?

Στις Σάββατο 27 Ιανουάριος 2007 15:05, ο/η Andreas Beck έγραψε:
> Pantelis <pakt223 at freemail.gr> wrote:
> > now, play it like this:
> > mplayer -vo null -ao alsa -af pan=2:1:1:-1:-1 test.mpg
>
> You can just use that while streaming from the device as well.
> I tune down video bitrate to 100kbit, which stops mplayer telling me the
> system is too slow to play. Maybe I should tune down video size as well.

Yep, of course you can, I was just being a bit anal. With a recording you
can apply several different tests and you know it is the same stream
so you can have more confidence in your interpretation of the results.

It is unlikely to make a real difference, but unlikely problems happen
just often enough to keep a technician/engineer humble ...

>
> > notice the added -af pan ...  This subtracts the right channel from the
> > left.
>
> Yes - I (24xxx device, Germany, some stations should be good enough, but
> got to use a good arial first, before I can say for sure) hear squeaking
> noises like from a tape bewing in extremely fast forwind most of the time.

I 'm not sure that this is very good news. If also the volume of this noise
is very low, then this matches what I 'm getting here with all stations and
in windows with _mono_ stations.

If it was stereo (phase difference) you should probably hear the same song
(no noise - not much anyway) with a noticeably reduced volume. Or if it
had positioning effects (like one instrument coming only from one channel)
you should be able to hear those.
 
>
> However this is heavily influenced by the setting of the
> ctl_mpeg_audio_mode control. Mono completely mutes the channel (no
> surprise), but Dual, Stereo and Joint Stereo already give a very audible
> difference - not only from mono, but also from each other.
>
> So I suppose there might be an extra issue with the MPEG encoding
> distorting phase differences.

Hmm, this is different here. I cannot hear any difference between the various
settings. Mono certainly doesn 't "completely mute" the output here.
The difference in windows is _very_ noticeable. Maybe this is due to the fact 
that you have a 24xxx device while I have a 29xxx one.

>
> So according to my tests, I do get Stereo, but the differences are
> rather weak. I should try to locate a classic or 60ies station that will
> play stuff with pronounced stereo effects often.

This shouldn 't matter. If ctl_audio_modes_present/cur_val is Stereo,
then you should get something different than the squeaky/bubbly/"fast forward"
sound.

>
> If someone has one of those little FM transmitters they now sell for
> attaching your MP3-Player to your car stereo (a few microwatts output,
> so they only work at very close proximity), they could as well use it to
> send a defined stereo signal and do further testing.

Yep, that would be nice :-) But I don 't think this is crucial as you should
be able to tell the difference in most cases (I 've tried this test with 
several mono/stereo stations in windows, it worked every time. Mono
stations produced the squeak, stereo stations the same song with reduced
volume)

-Pantelis
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