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Audio echo/delay/passthru problem
http://forum.linhes.org/viewtopic.php?f=6&t=5022		 Page 1 of 1
Author:  waffffffle [ Thu Jun 23, 2005 7:22 pm ]
Post subject:  Audio echo/delay/passthru problem
I finally got MythTV running on my Dell SC420 (SATA was a pain). I have a WinTV Go card and an old Soundblaster Live! card. I have the passthrough cable setup but I can't seem to get rid of this crazy echo when watching live TV unless the audio is way ahead of the video.

It seems like I would need to turn off the passthrough, but I can't figure out how to do that. I have alsamixer open right now, but I can't get it configured so that I have working audio.

It seems the two audio settings that effect what I hear are PCM and Line. If PCM is on then there is a huge echo. If Line is on then the audio is way ahead of the video. Actually even with just PCM on the initial audio somes on a about a split second before the video.

I can't seem to figure out how to fix this.

Any ideas? Thanks.
Author:  tjc [ Fri Jun 24, 2005 7:59 pm ]
Post subject: 
It's just like using a real mixer board, turn down or mute the inputs you don't want to pass through to the output. In this case, you don't want to listen to the input being recorded on "line" so you should mute it, you do want to listen to the playback "input" being generated by PCM.

The echo is because you're actually hearing two inputs one of them delayed with respect to the other (just like a real echo). The out of sync problem is because you're listening to the wrong input.

BTW - This is an FAQ, it gets asked and answered weekly, you really should have been able to find the answer to this for yourself via a search of the MythTV documentation or the forum. Just for example:

http://www.mythtv.org/docs/mythtv-HOWTO-7.html#ss7.2
http://mysettopbox.tv/phpBB2/viewtopic.php?t=4413

Please search first and ask questions when you can't find something that way.
- Remember to use the "search for all terms" option
- If the builtin search is returning too much or too little use the google site option
Quote:
site:mysettopbox.tv audio sync
Author:  waffffffle [ Sat Jun 25, 2005 1:05 pm ]
Post subject: 
I did search and I didn't find an answer.

Your links haven't solved my problem either. Setting the mixer exactly as stated does not solve the problem. With line muted and PCM on I still get the same echo. With the line unmuted it sounds the same other than that the initial sound (out of sync) is dramatically louder.

It seems as if the initial sound is bleeding into the pcm ouput. Does anyone know why that would be? Aslamixer identifies my sound card as:

Card: Sound Blaster Live!
Chip: TriTech id 3

I don't get it.

Should I invest in a better sound/capture card? I took the sound card from a dead ancient PC at work. I recently ordered my WinTV Go capture card for $20 online.

Thanks.
Author:  tjc [ Sat Jun 25, 2005 1:35 pm ]
Post subject: 
Did you plug the jumper into the right input jack? You didn't for example plug it into the microphone jack by mistake and fail to mute that?
Author:  waffffffle [ Sat Jun 25, 2005 3:10 pm ]
Post subject: 
Nope. The mic is muted anyways. It seems if I use the mic jack, set it as the capture and mute it, it has the exact same problem that I have with line. It seems like my card may be bleeding or something. I'm not sure though and I don't know how I can test this.
Author:  waffffffle [ Sat Jun 25, 2005 3:15 pm ]
Post subject: 
I think I got it. I had to turn down AC97 to zero.
Author:  tjc [ Sat Jun 25, 2005 7:04 pm ]
Post subject: 
'Kay now you're in charge of explaining this to the next newbie with the same problem around here... ;-)

BTW - You could also write this up on the wiki while it's still fresh in your mind and then you could just tell them to "look here on the wiki"...
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