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Clipping issues

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SaldivarClipping issues
by on Jun 7, 2007 at 9:15:45 pm

Hi,

I recently shot some video interviews with the Sony HDR-FX1 and the BeachTeck DXA-8 (an adapter that allows you to run two XLR mics into the camera).

Even though the sound levels on the camera looked fine the voices recorded have some audible clipping. If you look at the waveforms you don't see a noticeable peak but the clipping is still audible.
Also, after importing the footage into Final Cut Pro I notice that the levels never go beyond -12db.

As I already mentioned I'm editing these interviews in Final Cut Pro and also have access to Sound Track Pro.

Any suggestions on how to solve this?

Thanks a lot




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Rodney MRe: Clipping issues
by on Jun 7, 2007 at 11:05:16 pm

When looking at the waveform, any clipped areas will appear as flat spots at the height of the wave. Unfortunately, there's not really anything you can do to reverse the effects of clipping with the sound tools you have at your disposal.

It sounds as if one of two things is happening. Either the Beachtek's gain was set too high (the clipping occured at the Beachtek unit) or something is happening upon importing it into FCP. To get to some type of solution, I should ask a few questions. When you listen to the audio from the camera (through the headphone jack), do you hear the clipping? Also, what did you have plugged into the Beachtek - wired or wireless mics? If you were using condensor mics, did you have phantom power turned on? Were you using the limiters on the Beachtek?

One of the unfortunate things about the Beachtek is that there are no real level indicators or meters on it, so you're never really sure what your levels are (unless you activate the limiters and you see them light up). That's why portable sound mixers have tone generators built in, so that all gain stages can be calibrated to 0 dBu.



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SaldivarRe: Clipping issues
by on Jun 7, 2007 at 11:19:51 pm

Rodney,

Yes, I hear the clipping when I listen to the audio through the camera, with my headphones.

I don't remember how my BeachTek adapter was set up at the moment of the shooting but I can tell you that I was using two different microphones, one on each imput: a Sennheiser shotgun and an Audio Technica lavaliere, I hear the clipping in both.

Also, the problem might also be caused by the battery I was using on the BeachTek adapter. I remember changing it, among all the things I tried, and after that the clipping disappeared.

Thanks!

Javier







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Rodney MRe: Clipping issues
by on Jun 8, 2007 at 12:29:14 am

I was hoping you wouldn't hear the clipping from the camera, indicating that FCP was causing the problem. I'm sorry to say you are stuck with the clipping in that portion of the interview.

The battery going low appears to be the likely culprit, especially if you changed it and the clipping disappeared. The shotgun and the lavalier are both drawing phantom power (assuming they aren't powered by internal batteries) and probably are creating quite a draw. How long did the battery last before you started hearing the clipping? Are you using regular alkaline or lithium ion?



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Ty FordRe: Clipping issues
by on Jun 8, 2007 at 4:27:24 pm

No. You are hosed.

If you had been wearing headphones, you would have heard the distortion while you were shooting.

The correct answer to the question, "When do you listen to the audio going to the camera?" is ALWAYS, followed by ALWAYS, after which just plain always.

Regards,

Ty Ford



Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com
Download Ty Ford's "Existential Boogie" from iTunes now.


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