Move or cut less than 1/1000 sec from a clip?

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Move or cut less than 1/1000 sec from a clip?

Permanent link to this post Posted by EricMC » Sat Sep 30, 2017 1:53 pm

I've inherited a film soundtrack that seems to be a fraction out between left and right.

It makes all of the sound rather like the reverb you hear clapping in a very small room with smooth walls.

Looking at the difference between the wave forms, it looks as though I might be able to correct it by shifting one channel just fractionally to the left (by about .0004 secs)

Is it possible to move (or trim) clips by less than 1/1000 sec in Audacity?

— Of course, I don't know whether this will definitely correct the problem (perhaps it's too small for the ear to notice, and the reverb caused by something else?), as I can't find a way to select between hundredths of seconds.

Grateful for any advice.
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Re: Move or cut less than 1/1000 sec from a clip?

Permanent link to this post Posted by billw58 » Sat Sep 30, 2017 3:01 pm

0.0004 seconds is about 18 samples (actually 17.64) at 44100 Hz sample rate.

Set the selection format in the Selection Toolbar to Samples
Split the stereo channel
Zoom in at the start until you can see the individual samples.
Select 18 samples and delete.

Play back to see if that did the trick. Undo and try a different number of samples if it's not right.

Alternatively, if there is a place in the soundtrack where you have the same sound in both channels (especially a short, percussive sound), then you can split the stereo track, zoom in to the place where that sound is, and time shift one channel so the sound lines up in both channels.

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Re: Move or cut less than 1/1000 sec from a clip?

Permanent link to this post Posted by kozikowski » Sat Sep 30, 2017 3:05 pm

I don't know whether this will definitely correct the problem

But you can get a good idea by splitting the stereo show into independent tracks with the drop-down menu on the left. Mute one of the two tracks. I'm betting either track by itself is still going to have the echo effect. From your description, the echo is objectionable and easily heard. Half a millisecond isn't enough to do that.

While the show is split, you can Generate > Silence at the beginning of one of the two tracks, thus pushing it later. You can do that in milliseconds and down to individual digital samples

Screen Shot 2017-09-30 at 08.03.55.png
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Re: Move or cut less than 1/1000 sec from a clip?

Permanent link to this post Posted by Trebor » Sat Sep 30, 2017 3:18 pm

EricMC wrote:I've inherited a film soundtrack that seems to be a fraction out ...

There's free video-editing software called AVIdemux

It has a control where you can shift the timing of the sound-track ...

Avidemux video editor, shift sound-track ringed in red.png
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Re: Move or cut less than 1/1000 sec from a clip?

Permanent link to this post Posted by kozikowski » Sat Sep 30, 2017 3:25 pm

Isn't that for Picture/Sound sync or "lip sync?" That doesn't give you an echo.

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