tda9887/saa7134 background noise problem solved

[Eddy De Greef <edg1@xxxxxxxxxx>]

Hi,

the problem with the faint background noise in stereo mode on
my Medion7134 card is solved (April 6 - saa7134: faint noise in
stereo mode).
It turns out that I need to set two parameters of the tda9887
module to non-default values: qss=1 and port2=0
(Note: these parameters are only available in the latest v4l
snapshots).

By setting only the qss parameter, I can get the saa7134 module
to _detect_ the NICAM or FM stereo signal.
However, for all but one of the TV channels that I can receive,
the decoding of the stereo signal results in so many errors
that the auto-muting of the saa7134 chip kicks in and shuts
off the second audio channel. For some reason, this results
in a faint background noise.

To make a long story short: after a lot of experimenting I
found out that port2 of the tda9887 chip is used for automatic
gain control of the audio signal (at least on this Medion7134
card). By turning it on (ie. by setting the bit to 0), the
decoding errors went away.

I hope this information may be useful to other saa7134/tda9887
board owners.

Then I have the following question/suggestion to the v4l
developers: wouldn't it be possible to somehow store the
hardware-specific tuner settings in the saa7134 card
information list?
Once the saa7134 module identifies a board, such as the
Medion7134, I see no reason why it could no set hardware
specific bits in the tda9887 module.
I'm sure that such a scheme could save users and/or vendors
a lot of headaches.

Best regards,

Eddy


--

Unsubscribe mailto:video4linux-list-request@xxxxxxxxxx?subject=unsubscribe
https://www.redhat.com/mailman/listinfo/video4linux-list