audio out of sync

[jonwolf]

I recently filmed a convention and got the audio straight from a mixing board. The audio seems to be out of sync. Is there anyway to fix it. I tried just alighing it myself and that doesnt do the trick. It gets worse as times goes on. I recored the audio via xlr from a board as 'line'.

I need help. Deadlines are the worst.

 

[stanb17]

Jon,

Ah... the o'l sample rate monster has reared it's head. Take a close look at the sample rate your audio is in. The sample rate of an audio recording partially determines the overall sound quality. In the recording process, audio samples are saved to memory or disk; the rate each sample of audio input is recorded per second is the sample rate. The sample rate is measured in Hertz (Hz - cycles per second) and Kilohertz (kHz - thousand cycles per second).

CD quality audio has a sample rate of 44100Hz, 16-bit (resolution) and stereo (channels). The most common sample rates are 11, 22 and 44kHz, with most recording software supporting sample rates from 6kHz up to 192kHz. Like early footage filmed at a low frame rate looks flickered and robotic, the quality of an audio recording decreases as the sample rate is lowered. For audio recordings destined to be encoded to MP3, 22kHz is considered acceptable.

So... what does this have to do with sync'ing. I dunno. Doesn't really matter. What you need to do is either save the audio at another resolution, or... an oldie but a goody trick is to use stills over your motion footage, letting the audio run under it, then re-sync'ing the video when you cut back. If that is not an option, I would try saving the audio in a few differing resolutions (pick the obvious and standard ones first). Label each in some way so you don't get lost. You can also Google "audio sample rates" and find a great number of on-line resources to help you figure out whether you need to up-sample or down.
I've been in your shoes before. It's funny.. but obnoxious.

One more thing I just remembered... if you had to change video cassettes in the middle of the shoot, but the audio was on a single DAT or disc... make sure you account for the time it took to change tapes, reels or whatever. That's actually a quick fix and oft times results in you palm slapping your forehead.

Stan