7D FCP matching external sound

[Declan Smith]

Not sure if this is quite the right forum for this question, but here goes;

Captured clips from 7D converted into Prores 422(HQ) codec with native 7D sound, then imported sound captured form H4 recorder. Both audio sources report 16bit 48Khz sampling.

I have synced the external audio in the FCP timeline, however as the clip progresses, the sound starts to drift. This happens within 60 seconds.

Any ideas ?? Is this FCP related or the way h.264 -> editing codec translates?

[Bill Davis]

Declan,

Audio drift is most common when the sampling rate of two audio streams are different.

I'd double check the settings on both your 7D and on your H4. Make SURE they're not marching to two different drummers. I've seen instanced where a "setting report" indicated one thing, but the actual sample rate was something different.

It can't hurt to take your H4 audio and transcode it of them to match the other. You can do this simply in Quicktime Pro (which you own because you own FCP). Just load up your audio clip in QT - then Export it with the same settings used in your FCP timeline.

BTW, if you're using an H4 and not the newer H4n, there are stories of timing problems. So I'd also do a web search on that.

Let us know if that helps.

Good luck.

[Evan Donn]

I'm surprised this is happening with the 7D - with the 5D's 30fps you have to create a special custom preset with the correct timebase as detailed here:

25 Hour Day: DSLR Dual-System Audio: The 99.9% Solution

I assumed this would no longer be necessary since the 7d shoots 29.97/23.94 but my guess is whatever preset you're using has a timebase that doesn't perfectly match the camera's frame rate, so FCP retimes the audio on import.

[Declan Smith]

I think I must have messed up the sample rate in SoundTrack pro somehow for the external audio or the transcoding, as a second test setup worked as expected. Probably was recorded as 44.1 and converted to 48 as suggested by Bill.

So now, with pluraleyes plugin for FCP (suggested by Philip Bloom), my audio setup for the 7D sings!

Use external mics into H4 and use the H4 to record the audio whilst letting the 7D record it's crappy sound for syncing later.

[David Chapman]

Pluraleyes looks pretty cool. I don't know how I missed it before.

I just ordered the H4n and this is what I'm thinking....

1. connect XLR mic into H4N
2. split audio output for:
a: headphone monitoring
b: input for 7D (to record the same signal, but with the auto gain)
3. Match up video with better quality audio in post (now better waveform or audio source to sync up to)

Any problems seen with this that I'm missing?

[Brian Luce]

Originally Posted by David Chapman

Pluraleyes looks pretty cool. I don't know how I missed it before.

I just ordered the H4n and this is what I'm thinking....

1. connect XLR mic into H4N
2. split audio output for:
a: headphone monitoring
b: input for 7D (to record the same signal, but with the auto gain)
3. Match up video with better quality audio in post (now better waveform or audio source to sync up to)

Any problems seen with this that I'm missing?

I use Plural eyes with Vegas. It is brilliant and totally saved my butt this week. Don't tell clients about it, make them think you're syncing it all manually -- which is extremely labor intensive...as reflected in the professional fee.

Btw, my guide track for PE was recorded with an me66, dunno if the built in mic makes life more difficult for PE.

[Declan Smith]

Also, if you look at Philip Blooms website, there is an interesting link regarding pluraleyes and a code to use until 15/11/09 to get a discount.