Manually syncing audio and video

I received footage where they shot double system sound, they slated but they didn't record reference audio to the camera. Therefore, I sunk it manually. However, is there a surefire way to know if it's perfectly synced?

I nudge the audio a frame left or right and it still seems synced, it's just difficult for me tell if it's off by a frame or not, without reference audio.

> However, is there a surefire way to know if it's perfectly synced?

Yeah. Watch it. If it's imperceptible to a professional's eye, it doesn't matter anyway.


www.derekmok.com

Does your footage include any dynamic, noisy action? Hand claps or objects dropping for example? Parking on the frame were the contact occurs and looking for a spike on the waveform is always handy. P's at the end of words with pursed lips are not bad either.

Humans have a remarkable ability to force sync. After all, in nature light and sound travel at radically different rates. It is very hard for us to tell when things are out by 40 ms or less. Good thing too, as there are all sorts of things that conspire to trash sync in digital video. Image chips collect light for a frame or field before passing it along, meanwhile the audio records in near real time. Flat panel displays are also time vampires, as they assemble a full frame in a buffer before displaying it. Look us specs on monitors some time, they scare the heck out of me.

A properly engineered system accounts for some of these errors, but how do we know what kind of display our work ultimately ends up on?

> Does your footage include any dynamic, noisy action? Hand claps or objects dropping for example? Parking on the frame were the contact occurs and looking for
> a spike on the waveform is always handy.

I don't agree here. While sound spikes are great for when you have audio, the noises made by objects can be very hard to gauge. Certainly harder than the clapboard. I'd say, use the clapboard to find initial sync, then watch extended stretches of dialogue. And yes, you need a good broadcast-worthy system to judge sync.


www.derekmok.com

lets face it, if the slate is in sync, its in sync.

love what Derek said: "If it's imperceptible to a professional's eye, it doesn't matter anyway."
very zen master!

a slight drawback in FCP is that you can't slip sec on the audio that easily (Avid i believe has 1/4 frame increments, like 35mm)
so you might not get PERFECT sync. the clap could be 1/2 a frame out for instance.
in those instances, having the audio 1/2 a frame late is better than 1/2 a frame early.
(but is 3/4 of a frame late better than 1/4 early?)

simple tip:
if the bars on the PIC slate are blury, with a hint of solid, then it hit LATE in the frame

OK, now i said if the slate is in sync, it's in sync, but that's a bit simplistic,
it doesn't mean the at the entire shot is in sync, as there could be drift, or some other error (like you synced the wrong clap!)

so i always do a spot check of the clap, then a spot check of some part of the shot in the middle, and/or near the end.



nick

Last I recall, you can open an audio panel in FCP and slip the synch down to 100th of a frame.


- Loren

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