Synchronize 2-Audio Sources

BriceWilliams2 wrote on 12/3/2007, 1:24 PM
I have 2 cameras shooting a school play (1-shot gun mic per camera). 3-microphones on mic stands near stage connected to 1mixer that is feeding a stand alone flash recorder. This is separate from camera (Mini DV) audio and not connected in any way. I wanted to connect mixer to second xlr of my camera but didn't have proper adapter with me. (they called a few hours before the play) When I drop-in the audio file from flash recorder to the timeline, it was longer then the captured audio file of both cameras. The audio gets out of sync with in 3-5 seconds and continues to get worse. I have been cutting out small sections of audio during dead air to bring it back to sync, but doing this ever few seconds for a 2 hr clip is very time consuming.

I did try to render the flash audio file (mp3-44khz) to a standard pcm uncompressed 32khz file that would match my cameras. No luck
Tried changing pitch, slow up etc. No quick fix that I can find

Any suggestions? Or previous threads help. Thanks, Bill

Comments

Kennymusicman wrote on 12/3/2007, 2:41 PM
It depends on what software you have available.

What you could do, is extract the 2+ audio files form the videos into their own audio files. Then, align the beginning up together, and finally timestretch the second ones' ending to match the ending of the first.

It's a nice & easy trick in something like Cubase and takes all of about 30 secs.


Second trick, which is on similar theme, but keeping in Sony...
Take the 2 audio files as above, and find the same start on both, and note time. Then find same end on both, and not time. Calculate both durations, and time stretch latter to fit first, in SForge.



ps, I wonder if perhaps 1 camera was set to 44.1, and another to 48 sample rates by mistake? If so, correcting the sample rate will solve the problem
Chienworks wrote on 12/3/2007, 3:09 PM
Or in Vegas, Ctrl-drag the end of the audio event to match the end of the other material. No need to do any math at all. Just Ctrl-slide the end and you're done.
Kennymusicman wrote on 12/3/2007, 3:13 PM
Odd... I was going to suggest that, but when I tried it before to double check, it wasn't working for me. Tried it again, works fine this time. Hence why I "went round the houses"
pwppch wrote on 12/3/2007, 6:19 PM
BriceWilliams2:

Ctrl-Drag the ends of the audio you want to correct the duration/time of and match it to the correct audio.

Done.

A lot easier than breaking out the calculator approach or using Cubase.

>>ps, ...44.1, and another to 48 sample rates by mistake? If so, correcting the sample rate will solve the problem <<

How will this solve the problem?!?

Peter

Chienworks wrote on 12/3/2007, 7:05 PM
There does seem to be a contingent who believe that if the sample rates are different, the clips will play at different speeds. Not sure why. Hmmm, maybe some other software has trouble with this?

In Vegas, a 44.1KHz clip will play back at 44.1KHz*, with 44.1K samples lasting one second. A 48KHz clip will play back at 48KHz, with 48K samples lasting one second. So, no matter what sample rate, one second = one second. Vegas takes care of all the resampling automatically, invisibly, and on the fly. It's never a problem mixing them together in the same project.

*Assuming, of course, that the original recording device was really running at that speed. It may be off by a tiny bit, as was evidenced in the original question.
pwppch wrote on 12/3/2007, 7:24 PM
*Assuming, of course, that the original recording device was really running at that speed. It may be off by a tiny bit, as was evidenced in the original question

Exactly! Even worse, a clock source that drifts over time.

This is why we lock things to common clocks.

Also a good reason to place sound markers when recording. Even clapping hands together to provide some reference, though you can usually find something in both recordings to use as reference points.

Peter
Kennymusicman wrote on 12/4/2007, 6:31 AM
"There does seem to be a contingent who believe that if the sample rates are different, the clips will play at different speeds. Not sure why. Hmmm, maybe some other software has trouble with this?"

Because there are times when Vegas does play the things at different speeds.
pwppch wrote on 12/4/2007, 8:13 AM
>>Because there are times when Vegas does play the things at different speeds.<<

Really?!? Can you give me an example/scenario how you achieve this behavior?

Peter
Kennymusicman wrote on 12/4/2007, 8:46 AM
Yes, I will work on a repro for you.

In short, it can happen when I record audio in Vegas (say at 44.1)and at the same time record audio (from different source) in SF(say at 48).

Import the audio from SF into Vegas, but it does not correctly resample/compensate for different sample rate. Some of the time it does work as expected, but not always. I've even managed to recreate this with the same audio source just to confirm (for myself a fair while ago) when I thought there was a pitch change due to incorrect sample rate configuration.

I had narrowed it down at the time to Vegas locking onto a master clock stream (through a master clock via ADAT), and not adjusting non-matching sample rates to fit.

I will try and produce a repro for you at end of the week, can't play around with settings atm as I need to maintain my current settings for a few more days.
pwppch wrote on 12/4/2007, 11:36 AM
I am very interested in exactly how you do this.

I am curious as to why you would work this way?

However, it sounds like your audio hardware/drivers are not doing the right things.

So, to be clear:

Case 1:

You are recording in Vegas with one physical audio device (which one? ASIO? Wave?) and in Forge with a different physical device (which one? ASIO ? Wave?) Forge set to record 48 kHz and Vegas set to record 44.1 kHz.

Case 2:

Using the same physical device (which one?) in both Forge and Vegas. Forge set to record at 48 kHz and Vegas at 44.1. Which driver models are you using in each app?

If Vegas (or Forge) record at the project sample rate but the hardware is changed to a different and Vegas/Forge don't warn you, then you have a driver issue. We listen to ASIO sample rate change notifications. Wave has no way to tell us this, so if the driver is permiting this external change, there is nothing we can do about it.

Peter
PS: Please fill out your system specs in your user profile.

BriceWilliams2 wrote on 12/6/2007, 2:52 PM
Thanks for input. I didn't realize that my video/audio clip was missing 10-15 seconds. I must have stopped capture short of full tape. After I discovered this, I went back to Ctrl / Drag and everything is in sync and perfect. I wish I could have 5 hrs of my life back for my oversight. That's what happens when you edit in the wee hours of the morning. Any way Thanks again, much appreciated.

BILLL (third L is silent) ; )
Geoff_Wood wrote on 12/9/2007, 1:44 AM
One tip for lining things up. If there is a disticntive audio event near the start and the end, then these can be used as markers for stretching.

Hope that's relevant ...

geoff