Precision cuts - light and sound

FoskeyMedia wrote on 6/13/2015, 9:51 AM
I do a lot of music and dance videos. Oftern they require precisions cuts to an exact beat. My preview seems to lag sometimes and so I'm not sure if that video cut is RIGHT ON the click. I read somewhere that because light travels faster than sound ..you should cut slightly ahead of when you want to see it. Any words of advice or formula on this ?

Comments

ritsmer wrote on 6/13/2015, 10:17 AM
Simple - but it works: Normally I just preview the audio track solo and set markers to the beat - then you have these markers to synchronize the video cutting....
... however it is often not enough just to preview once to be able to place the markers correctly - you may have to hear the music several times to get familiar with the actual beat which is not always simply 4/4 or whatever.

When the video tracks are finished I render to some mpeg-2 720 25p at just 10 Mbps which just nearly any player can play at full speed to check if video and audio is well synchronized.
musicvid10 wrote on 6/13/2015, 10:24 AM
A slight delay (5-20 ms) is common if you are slipping the audio to a visual sync point.
Never let the audio lead the visuals; it will sound wrong.

Sound travels at 1100 feet/s under average conditions.
So 36.7 feet per video frame (30fps) is a useful reference for surround mixing.
In practical use i assume the listener is midway between front and back of house, so the delay sounds best when reduced to half its calculated value.
FoskeyMedia wrote on 6/13/2015, 11:54 AM
When I find the spot that I need to click audio and video I usually go down to almost sample level and sync... sometimes it looks like the vid is slightly behind on playback. It could be perception, fatique, bad video card....What I'll also start doing is rendering just those few seconds and play back to see if it clicks.
musicvid10 wrote on 6/13/2015, 12:24 PM
Start with a 5 ms audio delay and work up from there.
Exact sync has never felt right to me.
FoskeyMedia wrote on 6/13/2015, 9:03 PM
Thanks....
I think one of my issuse it my PC and graphix card. When I rendered and played back this last project it was perfrct. It's mainly in preview I get confused. I'm finding I have better luck if I line it up visually with the track and don't depend on the preview window.

Chienworks wrote on 6/13/2015, 9:07 PM
Do you know about dynamic RAM preview? Highlight a short selection around your possible edit point and press Shift-B. This causes Vegas to render that section to memory and then it will play back in preview full speed. Depending on how much RAM you set aside you might not get more than a few seconds at a time, but it's probably enough to assist you with this sort of thing.
musicvid10 wrote on 6/13/2015, 9:37 PM
Kelly makes a good suggestion.
You've probably got audio latency.
Hook in to your asio drivers directly from Vegas.
Don't use windows mapper..

PeterWright wrote on 6/13/2015, 9:40 PM
Yes, as Kelly says, Dynamic Preview is great for a quick preview of how a cut looks..

Whilst cutting on a beat can be dynamic, you also need to listen to the phrasing of the vocalist - a singer will often anticipate the timing and sing just before the beat - if he or she does this it can be jarring to make a cut halfway through a word, so an early cut is better.

It doesn't work the other way so well though - if the singer phrases a line late, a late cut seems wrong - better to do the cut on the beat and be there ready for their "late" entry" (Sinatra often did this)