You need two audio files to synchronize (or ‘sync’) your rip of the VHS audio track to your HD video.
- The audio file the VHS audio track (which you have already)
- The audio file of the HD video audio
Since you are already using Audacity, will use that as an example.
Open both audio files
Compare the waveforms of each file–look at the head-end and the tail-end of each file and line up the VHS audio file to the HD file by the waveforms. If your VHS audio track doesn’t ‘line-up’ with the HD audio file, then you have to either extend or shorten the duration of the VHS audio.
There’s some YouTube videos, out here, that help you ‘line-up’ or synchronize audio files of instrumental tracks and vocal/instrumentals tracks of the same song (to make a ‘vocal-only’ audio file). Get tips on synchronizing the two files from these videos.
After you line-up the files together, ‘select’ the VHS audio file, then go to: Effect–>Change Tempo.
You have to put in the percentage value that will determine the right length of the VHS audio file to match the length of the HD audio file. This way, you change the duration of the stream, but you are maintaining the pitch.
After you change the duration, compare the waveforms of the files again. If they don’t match up, then you have to try again. Keep playing with the percentage values until the waveforms on each ends of the audio file match-up.