[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 14:45:14 UTC 2005


Sorry,

I forgot to mention that I am using mythtv 0.18.1.20050510-1, installed 
via Gentoo's portage (Gentoo calls this 0.18.1-r2). I imagine you would 
all want to know that :-)

Michael

Michael Cowell wrote:

> Hi all,
>
> I am also experiencing a problem like this. I have the following setup:
>
> AMD Duron 1 GHz
> 384 MB SDRAM
> 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 You might think my box is outdated, that's because it is!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.
>
> Thanks,
>
> Michael Cowell
>
> Sérgio 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 Sérgio 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.
>>>
>>>
>>> Sérgio 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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