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help with correct audio levels
I shoot using my GL-2 with a Beachtek and wireless lavs. I set manual audio levels on the camera to keep them in the acceptable range, hovering around 12dB. I’ve always gotten really good sound doing this.
I recently had a shoot requiring two wireless mics and a boom, so I hired a professional sound person to record and mix from the three sources on to the two channels of the camera. She did a great job, but as I’m looking at the footage in PPro 1.5 where I edit, the file has the classic flattened tops and bottoms of audio that has clipping. On the audio mixer in PPro 1.5, it never goes into the red “clipping” zone, but it does sound a little hot, and I’m concerned about the tops and bottoms of the file being flattened like that.
When I asked the sound person about it, she replied:
“Be sure to check what you set your system up to read at the head of the tape. Tone for what we shot was at -20db not 0db.
Perhaps the program set a default for tone at 0 db?”The GL2 doesn’t have an option to set bars and tone as far as I know, so I didn’t set tone in the camera.
In the PPro documentation it says:
“Some audio workflows must be calibrated at a specific tone level. The default level of the 1-kHz tone is 012 dB referenced to 0 dBfs. You can customize the tone level to match your audio workflow by choosing Clip > Audio Options > Audio Gain with a clip selected.”It seems that doing this and setting the gain to -20dB just makes the audio very low, not resolving the flattened tops and bottoms of the file.
I don’t have experience or really understand the implications of what having tone set at -20 vs. 0dB means, or, if this does mean that the files are clipping, even though it doesn’t appear so on the meter, how to re-calibrate within PPro 1.5 to make it right.
Any help here greatly appreciated!
thanks-
Ruby -
1 Reply
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Unfortunately you can’t set an audio level on capture with 1394…how it was recorded on tape is how it gets captured. If the tops of you waveforms are flat…they are flat on the tape as well.
With analog audio (such as audio from a Betacam VTR), you would set the recording level of the analog capture using the tone at the head of the tape to set the level. In that scenario, if the level for analog capture was set too high, the audio would be clipped even though the waveforms have been recorded correctly on the betacam tape. Analog audio can go well past 0db, and not suffer, however with DV audio, 0db is the max…anything above it is clipped.It might be interesting to capture the tone at the head of the tape and open Premieres mixer and see what that tone is at. -20db should have given enough head room to prevent clipping for normal conversational levels.
Possible causes for your problem, might have been if the mixer was set to “line level” output, while the camera was set to “mic level”. Some cameras also have internal limiters that could clip the audio input at the jack if the level is too hot…I think the XL1 cameras had a problem with that.
Also, If your audio guy didn’t ride the levels to lower high volume areas (screams, yells, etc…) it could have clipped.Erik
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