Fixing out of sync Audio

[Wingston]

Bear with me. This is an audio question. I have captured many hours of VHS recordings on my mac using VideoGlide from EchoFX. Stupidly I didn't check it all properly. Got rid of the tapes and then found my sync problem. I know what the issue was now. In the VideoGlide audio settings, I have a choice of 'Size' - 8 bits or 16 bits. I have to be honest. I don't know what that is or means. But it was set to 16 and when I changed it to 8 - problem solved.

What I want to know is - is there any way to fix the captured files by separating the audio and making it the length/speed, or whatever the 8 bits setting would have done before putting it back with the video?

Cheers

Phil

[jagabo]

You don't have to extract the audio. Most A/V editors will allow you to change the audio length and skew. Try VirtualDub2.

[Cornucopia]

Yeah but 8bit audio is gonna sound like crap!

"Got rid of the tapes"? Smh.


Scott

[jagabo]

Yeah but 8bit audio is gonna sound like crap!

Probably better than no audio.

[Wingston]

The 8 bit audio sounds fine on the ones I am capturing now. I have premiere pro and FCP7. Will they do it?

[Wingston]

Yeah but 8bit audio is gonna sound like crap!

"Got rid of the tapes"? Smh.


Scott

Yes, i dumped the tapes.

[abolibibelot]

Yeah but 8bit audio is gonna sound like crap!
"Got rid of the tapes"? Smh.
Scott

Yes, i dumped the tapes.

SMH = “Shaking my head” (implied : that was dumb).

[Wingston]

Yeah but 8bit audio is gonna sound like crap!
"Got rid of the tapes"? Smh.
Scott

Yes, i dumped the tapes.

SMH = “Shaking my head” (implied : that was dumb).

Something of which I am well aware

[Wingston]

So, can anyone tell me exactly how I do this? I have video editing software but there is no 'reverse to 8 from 16 bit button'. Is there a percentage by which to reduce or anything?

[jagabo]

Pretty much every video editor will allow you to change the audio sample size and sample rate. Here's VirtualDub2's Audio -> Conversion... dialog:


[Attachment 56395 - Click to enlarge]

But capturing 8-bit audio is a huge compromise. I highly recommend you figure out how to get 16 bit audio capture working properly. For video you should usually be capturing 16 bit, 48000 Hz, stereo (2-channel).

[abolibibelot]

But sample size and sampling rate have nothing to do with the synchronization issue, which could be due to either random dropped frames, or a wrong framerate setting. If dropped frames are the cause, it's not going to be an easy fix. (Unless there are sophisticated methods I'm not aware of to deal with that sort of problem automatically — not an expert in that particular field, but I can't see how missing frames can be detected on a single digital transfer with no possibility to go back to the analog source.)
Is the audio shifting forward or backward, and is the shift slowly increasing from the beginning to the end, or are there specific spots where it increases suddenly and then stays stable for a while ?

[lordsmurf]

So, can anyone tell me exactly how I do this? I have video editing software but there is no 'reverse to 8 from 16 bit button'. Is there a percentage by which to reduce or anything?

Advanced restore work will be required to attempt to make it sound richer than 8-bit, but understand it'll never again be 16-bit or better quality.

SMH = “Shaking my head” (implied : that was dumb).

I've also seem it as "smack my head", but same thing.

due to either random dropped frames,

99%+ the case

or a wrong framerate setting.

Unlikely.

If dropped frames are the cause, it's not going to be an easy fix.

Or fixable whatsoever. Drift is asynchronous.

(Unless there are sophisticated methods I'm not aware of to deal with that sort of problem automatically

Nope.

but I can't see how missing frames can be detected on a single digital transfer with no possibility to go back to the analog source.)

Correct.

Is the audio shifting forward or backward, and is the shift slowly increasing from the beginning to the end, or are there specific spots where it increases suddenly and then stays stable for a while ?

Mostly like the answer is "al of the above", depending on clip location. This is what happens when not using a TBC, and also using a crappy capture card. What's really sad is when "professional" (hack, quack) transfer services do this. Seen it, far too many times.

[dellsam34]

What the bit depth has to do with audio sync, If it sounds like chipmunks than it could be the sampling rate Khz not the bit depth, If it's lip sync then you may have to detach the audio and reset the length and re-attach it again.