Audio Sync issues

[Chris Wright]

I'm working on a wedding video with multiple sound sources. So far I have my wireless on the groom, a cardiod on-camera mic, and a GL2's on-camera mic all sync'ed just fine.

Now I have a cassette tape of a recording from the church's mixer, which gives me audio from the pastor's mic, the piano, the guitars, and singers. I used my GL2 to import the audio from my cassette player into the computer, so now I have a digital file. However, every time I sync this audio file to my other audio tracks, it seems to drift, and doesn't remain in sync. It's almost as if it's playing at a different speed than the other tracks.

I'm working in Final Cut Pro 4.5, if that makes any difference.
Is there any way to fix this?

Thanks!

[Wayne Starick]

Hi Chris,

I would suspect that the major problem lies in the original cassette recording - this medium, according to the experts, will always exhibit drift. Even though you have then imported the audio, you always take the original drift with you (does that make sense??)

I always use my trusty mini-disc recorder as well as my iRiver and have never had any problems with drift as these are both digital devices as opposed to the analogue cassette recorder.

[Patrick King]

Chris,

Two options I can see for you to sync the digitized cassette audio:

1. Sync the beginning of the digitized cassette audio. Then find a place as close to the end of the digitized cassette audio that you can positively sync with the other sources. Sync that point by increasing or decreasing the length of the digitized cassette audio event on the timeline. Now check points in the middle to see if they are in sync. If they are, the playback rate of the digitized cassette audio was just different than the pure digital sources and you're good to go (Vegas will change the length of the event without pitch shifting, don't know about other NLEs). If the middle sections are not in sync with the other pure digital sources, then proceed to 2.

2. Segment the digitized cassette audio into smaller audio events and manually syncronize each segment. You will only need to syncronize the segments that have audio that no other source has (pastor speaking, musicians playing), don't even add the other segments to the timeline.

[Chris Wright]

Thank you very much for the replies. Patrick, I will try your suggestions today.

Fortuneately, It's not critical that I use the tape. My wireless lav on the groom pleasantly surprised me by picking up the bride, groom, pastor, and music wonderfully. but the signer and piano were both mic'ed by the house system which is what I have on the tape. If I can get the tape sync'ed it will sound a little better, but it's definitely not necessary.

[Steve House]

Inconsistent tape speeds and tape stretch were the bain of double system sound in the pre-digital days. To remedy it, movie audio was/is recorded alongside a track of synch tone - the most common system was called Pilot-tone - cabled over from the camera that varied with the speed of the camera. Other systems used a matched pair of crystal controlled clocks to both generate the recorded tone and control the camera motor speed. The recorded tone was used to control the speed of a post-production dubbing device that transferred the tape masters to magneticly coated sprocketed filmstock so that there would be a one to one correspondence between a frame of picture and a frame of sound. These were then aligned mechanically in an set of ganged sprocket wheels called, surprisingly <g>, a synchronizer for editing. If you look at a picture of a classic Movieola editor you'll see it has two film feed and takeup reels side-by-side - one is the picture film and beside it is another feeding magnetic stock with identical sprocketing for the sound.

DAT, miniDisc, memory cards and other digital recording devices make double system sound for DV much easier since the clocks in both the camera and recorder are stable enough to run at identical speed over reasonable shot lengths and it's relatively easy to correct any slight drift that might occur. But use an analog recorder like a cassette tape and all the synchronization gremlins of the moviemakers of the 1930's come roaring back to haunt you. Both film movie cameras and DV video cameras are run at very stable speeds but analogue audio is all over the place, its speed varying wildly (compared to a video camera's clock) even from place to place within the same continuous reel of tape.

[Patrick King]

Steve,
Great explaination of why the analog audio might be out of sync; you obviously know far more about this topic from your personal experience that I do. Can you recommend any other options than those that I laid out above (do you even consider them valid)? Your vast experience in this area may provide a shortcut that I'm not aware of and save Chris precious time (and sanity).

[Steve House]

Your suggestions seems spot on to me, coupled with trying to use fairly short shots so the synch doesn't drift too much during the shot. Look at most theatrical films and broadcast video programs, commericals, etc you'll see they tend to use far more frequent cuts than you see in many videos for weddings etc. Try counting the number of cuts in a beer or auto commercial, divide into 30 seconds running time, and you'll see they're put together in shots averaging 2 to 5 seconds on screen. It might be a PITA to sync up wild sound with that many cuts but it should be doable with decent results.

[John DeLuca]

The sampling rate of digital video is 48khz...... I didn't think cassette or mini disk recorded at that sampling rate, but I could be wrong ;-) A great way to do the audio at a wedding is running four wireless kits into a field mixer like the rolls mx422, wireless shotgun taped on podium, priest omni lav, groom omni lav, and optional bride omni lav. I wouldn't even mess with the church board unless I was forced to. Pan and mix your channels, then run solid XLR to one or more cams. If you have prem pro 1.5 you can scrub in real time between cam A and cam B with the multi cam plug in(no worries about audio sync, both cams have main audio). If your doing alot of weddings time is a valuable asset.

John