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Audio lag caused on 1 track mono files?

Last response: in Home Audio
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June 18, 2011 5:26:51 PM

Okay I've been trying to fix an audio lag problem for a couple days now. At first I thought it was because I was running seperate lines from my video and audio (two different cards) so I bought a card that supports HDMI video and audio with a single connection. However the video file I was testing the sync with still had a slight lag. After looking over things a bit more I noticed my test file had a 1 track mono audio. So I tested some other video files with 2 channel stereo and it seems like the lag is gone. Could the lag have been caused by the fact I was playing a mono audio file on an HDTV that supports digital audio?
June 19, 2011 7:54:36 AM

of course it could be.
if the track was TRUE mono, then there would be some activity needed by the audio processor to split the mono signal and send it to each speaker.

the mono nowadays is actually two tracks, one for the left and one for the right.
if this was sent to the television, then there would be no activity needed of the audio processor.

there are three choices:
1. a single mono track on ONLY the left or right
2. a TRUE mono track that combines the left and right into one track that doesnt care if it leans left or right.
3. a more modern mono track that contains the exact information on both the left and right channels.

when the audio has seperate information for the left and right speaker, that is stereo.
when the audio has the same information for the left and right, that is mono.
it is probably best to say, the audio track doesnt have to have a left/right flag OR there is only one flag for the left (or a flag for the right)
and the television says 'NO.. i am not going to play audio on only one speaker'
so it is copying the audio from one side and playing it on the other side.

chances are, there is probably at least one flag.. and the copying of the audio is the delay you are seeing.

maybe you can download virtual dub.. extract the audio from the video, put the audio into a wav editor.. copy the audio track and add it again for the other channel.. save the new audio track, put it back into the video with virtual dub and save it.
playing that new video with the updated audio tracks should stop the televisions audio processor from having to do anything except amplify the signal.

if that doesnt work, then the video itself is not in sync with the audio.
there is a program called 'reclock' that will adjust the audio and video, but the algorithm is probably for the well known decoders and compressors that put the lag there in the first place.
so if you make the audio and video out of sync by 3ms on purpose, i dont expect reclock to fix that for you.
and even then, you could use virtualdub to increase or decrease the audio track to be in sync again.

i have closely watched audio that is not in sync.. and i can clearly see that the audio shifts from 'on time' to 'late' and 'more late' as it shuffles through the movie.
you could try to use the simple audio correction and retard the video by 2ms .. but the audio and video will still show signs of being out of sync.
this is when reclock can help.

the poor programs that rip the audio and video, they will cause the latency.
that is why you see movies downloaded from the internet with audio and video out of sync.

it is really bad, and really stupid, to ruin the audio and video sync.. because the person can always subtract quality from the video.
everybody that downloads a movie off the internet has the chance to see the video with less detail.
to ensure absolute highest video quality, you gotta go rent the movie.

if you think it is bad for video.. audio does it every single bloody time.
you try to get the 96khz version of a file (even when the license says it is legal) but the uploader compresses the audio with flac to save hard drive space and uploading/downloading times.

since CD quality is junk as it is, the effects are negligable with that sample rate and bit depth.
as the sample rate and bitdepth gets higher, the difference will be much more noticeable.

**edit**
you might be really poor and cant afford to rent (like me) .. but that doesnt mean you should be left out.
this economy is moving quickly, and anything that is old will become impossible to find.
for an example..
look at all of the dance music from the late 1990's / early 2000 era.
there were hundreds of songs playing on the FM radio.. and you cant find those songs anywhere (usa songs anywho)
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