[mythtv-users] Crackling and popping in non-PVR analog card -- I think I can say it's MythTV's fault

Michael Cowell michael at mousewasher.dk
Sat Sep 3 14:39:04 UTC 2005

Hi all,

I am also experiencing a problem like this. I have the following setup:

AMD Duron 1 GHz
Twinview DVB-T capture card
Pinnacle PCTV bt878 based capture card
SBLive! emu10k1 based audio card

Linux distro is Gentoo. Kernel version is 2.6.12-gentoo-r8. I am using 
unpatched V4L.

Obviously the popping / clicking occurs only with the analog card.

You might think my box is outdated, that's because it is! Interestingly 
I had this same hardware running MythTV 0.15 a while ago, also with 
Gentoo and a 2.6 series kernel (I think it was around 2.6.2 back then), 
but there was no clicking.

My CPU does not max out when doing analogue recording. I have tried ALSA 
and OSS, and have changed recording levels extensively. This did not fix 
the issue.

I don't mind the popping too much because I only use the analogue card 
when the digital one is busy.

I mention this because it seems to me that my experience indicates that:

1. This does not appear to be a hardware fault (I had clear audio going 
using this hardware before software upgrade).
2. This does not appear to be a capture card problem (my capture card is 
different to Sergio's, at both the board and chipset level).
3. The emu10k1 chipset is a common factor here. Maybe that is the 
problem. I imagine the driver has had a lot of work since 2.6.2.

If I can provide any more information please let me know. This problem 
interests me because I can't see a clear reason for it occurring. The 
distortion "sounds analogue" (like clipping / RF interference), but DSP 
is so advanced these days that this could easily be a digital hardware / 
software issue.


Michael Cowell

SÚrgio Gomes wrote:

> David Ellis wrote:
>> Lower your volume level on the card setup in mythsetup.........I 
>> think the
>> problem is with an input volume level that is too high.
>> David
>> -----Original Message-----
>> From: mythtv-users-bounces at mythtv.org
>> [mailto:mythtv-users-bounces at mythtv.org] On Behalf Of SÚrgio Gomes
>> Sent: Friday, September 02, 2005 5:00 PM
>> To: mythtv-users at mythtv.org
>> Subject: [mythtv-users] Crackling and popping in non-PVR analog card 
>> -- I
>> think I can say it's MythTV's fault
>> Hello everyone!
>> I'm probably one of the very few people left with a non-PVR analog 
>> card (a simple Hauppauge WinTV Go, based on cx8800). The audio goes 
>> from the TV card to the sound card via a simple external stereo 
>> cable, as I'm sure is the case in many setups out there.
>> Now, I have been having a problem with audio on my MythTV since I 
>> installed it yesterday: I get a lot of crackling and popping in my 
>> recordings and in LiveTV. I've been running several tests.
>> Outside MythTV:
>> - The audio gets to the sound card in great quality: if I turn on 
>> playback of the line-in channel, the sound is perfect
>> - It is also not the recording hardware of the sound card that is 
>> ruining the sound, as both "record" and "arecord" record perfect sound
>> - "record" and "arecord" still record perfect sound with high CPU and 
>> disk loads
>> - "record" and "arecord" record perfect sound whether or not video is 
>> playing (with XawTV, for instance)
>> - If I start recording sound then start mythfrontend and select 
>> "Watch TV", it won't get any sound (understandable, the device is 
>> busy), but the "record" or "arecord" program will keep on recording, 
>> and the sound is, once again, perfect
>> - Recorded MythTV shows play with crackling in mplayer
>> Inside MythTV:
>> - The amount of crackling (or at least the loudness) goes up with the 
>> loudness of the broadcast; if it's quiet there's almost no crackling, 
>> but if there are a lot of people talking or loud sounds, there is a 
>> lot of crackling
>> - Happens with ALSA and OSS
>> - Happens with MJPEG and MPEG4
>> - Happens with or without "Agressive Sound Buffering"
>> - Happens with both WAV and MP3, at any of the available rates
>> - Happens with or without internal volume controls, at any level
>> - Music and videos play without any problems
>> - The amount of crackling goes up with the quality of the video; 
>> there is almost no crackling at 160x160, but a lot of it at 768x576
>> So, given all this I think we can rule out any interference on the 
>> sound from external sources, hardware or other software, and assume 
>> the problem is limited to the TV functionality in MythTV. My guess 
>> would be that the sound is being clipped due to volume adjustments 
>> inside MythTV, and is only then recorded, assuming that MythTV does 
>> some volume processing on the sound (even if just boosting it).
>> Now, this is all fine and well and a good theory until the last 
>> point. I don't understand why the problem gets worse with higher 
>> video resolutions. That completely ruins my theory. With that in 
>> mind, I guess the problem could only be some kind of multiplexing or 
>> demultiplexing bug (probably multiplexing, because for it to be a 
>> demultiplexing bug it would also have to be present in mplayer), but 
>> that wouldn't account for the problem getting worse on loud samples 
>> (since WAV is constant bitrate).
>> So, I'm hoping someone who knows MythTV better than me can help me 
>> out with this... I'll gladly provide recording samples if anyone 
>> wants them. Here are my PC specs:
>> - Athlon 64 3200+
>> - NForce 3 motherboard (ASUS)
>> - Gentoo Linux with 2.6.12-r5 gentoo-sources kernel
>> - video4linux CVS (due to some cx8800 problems with the release 
>> version). --> shouldn't be the problem because of all the above reasons
>> - WinTV Go 2 with cx8800 chip
>> - Audigy 2 ZS (snd-emu10k1 module), with hardware mixing
>> - MythTV 0.18.1 compiled from source in AMD64 (as the rest of my system)
>> - Using PAL BG
>> Thank you for bearing with me through this exhaustive description.
>> SÚrgio Gomes
>> _______________________________________________
>> mythtv-users mailing list
>> mythtv-users at mythtv.org
>> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
> Well, I've tried that and it still happens :-/
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