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MisterP 09-06-2013 06:08 AM

Audio AGC problems with CX23885 based DVB-S2 card
I am running 32-bit lubuntu and XBMC with a DVBSKY S952 PCIe card as part of my media centre project.
I am using the DVBSKY-provided V4L modules to get the S952/cx23885 working.

Everything is working, but the TV audio sounds nasty. It sounds like AGC is being applied, so background noise goes up and down depending on whether people are speaking. I believe this is called pumping.

Music/DVDs etc. sound OK, so it is not a general audio problem.

I cannot find a detailed datasheet for the chipsets, so I cannot decide if this problem can be adjusted in the driver.

Card: DVBSKY S952 using Conexant CX23885 and Montage DS3103/TS2022 chipsets.

The cx23885-dvb.c code contains AGC fields, but these seem to relate to analogue broadcasts:
static struct dibx000_agc_config xc3028_agc_config = {
BAND_VHF | BAND_UHF, /* band_caps */

Does anyone have any ideas on:
a) whether the problem can be adjusted.
b) where I can get a spec of which ports/values need to be used if adjustments can be made.

Guesswork and fiddling with the agc fields in the structure have made no noticeable difference. They may well relate to the RF not audio gain.

alan@xbmcal:~$ uname -a
Linux xbmcal 3.8.0-30-generic #44-Ubuntu SMP Thu Aug 22 20:54:42 UTC 2013 i686 athlon i686 GNU/Linux

alan@xbmcal:~$ lspci
02:00.0 Multimedia video controller: Conexant Systems, Inc. CX23885 PCI Video and Audio Decoder (rev 04)

Your help would be appreciated.


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