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

SÚrgio Gomes sergiomdgomes at netcabo.pt
Sat Sep 3 13:45:18 UTC 2005

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.
>-----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

Well, I've tried that and it still happens :-/

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