Audio off-sync when recording live music onto VHS?

[Ravenandkites]

Hi all, this is kind of a different project than this site typically deals with but we've been recording live shows with a handful of analog cameras, some switchers, and a video mixer and running the audio into the VCR.

This setup will sometimes get out of sync (especially when using a cheap hard switcher to change cameras) and it makes it hard to line up audio if we have a separate audio source when editing the video digitally.

A friend tipped us off on TBC but I'm not sure I quite understand. Say we bought a VCR or mixer with TBC, would this fix the audio sync issues? If we had a mixer with TBC but fed it into a cheap VCR would we still have similar issues? Is there a cheap option to get what I want without having to by a super nice VCR?

[lordsmurf]

Lack of TBC often results in dropped frames, which cascades into audio sync errors.

Why record audio on VHS?
That just seems strange to me. I'd use pretty much anything else. Even back when VHS was 'in' format in the 80s and 90s.

[Ravenandkites]

Really, we are just shooting live videos and full sets of bands and using cheap equipment that we have. Ideally we just shoot the sets, digitize them, and upload to YouTube. But there have been some audio issues and so we've been recording audio separate too. If we need to use that back up source the original audio on the VHS is important for syncing.

Another question I have is: if we got a mixer with TBC going into a cheap VCR without TBC, that could still result in dropped frames and sync issues right? So if we were to invest we should get a VCR with TBC instead of a mixer.

[dpalomaki]

To minimize audio sync issues, first it is best (but not vital) to give the same audio feed to all cameras.
Analog video mixers, such as the Videonics MX series do provide a basic TBC function and can preserve audio sync among several sources being mixed (switched) to one. They are good for live mixing, and can be used in post for analog sources with a bit of skill and cunning, either with an edit controller or by syncing the playback sources. They also allow mapping audio as well; e.g., same audio source no matter which video feed is used.

Audio sync issues arise from both dropped frames in capture, and may appear at any time if the audio and video paths have different latencies. Not unusual on PC when using different cards for audio and video capture and/or playback. Always judge sync on the final product. They can also result from "slow" PC that can not keep up with speed needed for video capture or that have too many other processes eating processor and drive time. Audio leading video is generally worse than audio lagging video (because light travels faster than sound - and ears are used to that). For every ~33 feet you are from the speaker, the sound will reach you about one frame later than the light.

If the audio and video feeding the VCR are in sync, the VCR recording should be in sync. A TBC at the VCR input signal will help assure a in spec. signal reaches the VCR, but may not be necessary on live camera feeds or the output of a decent video mixer. And it does not guarantee you will not need a TBC on the VCR output when playing back a tape. Cheap VCR (original cost) results are often marginal at best and finding good VCR today is problematic.

If using VHS (or S-VHS) to record audio, I trust you are using a stereo Hi-Fi track (which will give about FM radio quality), not the linear audio track (usually mono) which is closer to AM radio quality. Using a separate analog audio recorder, such as a cassette deck, can lead to audio sync drift issues if its speed varies or a different playback unit is used. Using modest cost digital recorders can eliminate this drift issue.

Achieving audio sync can be aided by using an impulse sound source such as a clap board or rim shot to guide alignment. If your edit software shows audio wave forms that can be a significant aid as well.