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Old February 12th, 2007, 09:58 AM   #1
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Audio Meter says ok, but clipping is still happening?

This may have been answered in another thread, I couldn't find it....

I recorded an interview with my JVC HD100UA. We put a wireless mic on the interviewee, and plugged it into channel 1. We also set up a shot gun mic and plugged it into channel 2. I haven't touched any of the audio settings on the camera.

We had the volume meter on the camera, and we were using DVrack.

We cranked the volume on the camera all the way. That made it loud, but the meters on the camera and dvrack did not show any clipping.

When I play it back on my computer ( I bought decent speakers for it) it sounds fine. Maybe a few bits where the person gets a little emphatic it sounds a bit too loud for one syllable, but not bad. I play it back on Adobe PP2.0, and the volume meters in the NLE don't show clipping.

I burned it to a dvd, and someone watched it on their tv. They said they heard clipping.

I have to do a lot of research, of course. I'm wondering whether I really have clipping going on, or whether I just need to lower the gain on those bits in post? Do I need to change settings on my camera to get an accurate read of the volume?
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Old February 12th, 2007, 10:31 AM   #2
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Dennis,

you didn't say much about what steps you went through between the recording and burning it to a DVD. It is certainly possible to introduce audio gain in the sound processing there that could lead to clipping later.

I would suggest that while you prepare your audio for the DVD, look for peaks and make sure that there is nothing at all above -6dB in any audio channel. Some may suggest to go even lower, to -10dB. Then create your DVD.

Apart from clipping, this brings the audio level of your DVD in line with professional DVDs such as those of feature films. If your audio goes all the way up to 0dB - with our without any clipping - it'll sound much louder than what viewers are used to. Limit your peaks to -6dB, and viewers won't need to rush to the volume control when they play your DVD.

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Old February 12th, 2007, 11:59 AM   #3
 
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Actually, as long as your peaks don't exceed 0 dB, there should be no clipping. I like to run with about -.1dB headroom. You have the option of putting a limiter on your audio track, either in the HD110, or in post processing. If you're already experienceing some minor clipping, you can probably fix it with a small amount of compression or limiting.
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Old February 12th, 2007, 02:40 PM   #4
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Another thing to check is the volume on the wireless reciever and/or transmitter itself. I've been an audio guy for almost 18 years. If your gain is set too high on your wireless receiver and it is clipping, it won't necessarily show in your camera monitor. If you're "throwing a distorted signal" from the beginning, it will be distorted until the end. With the HD-110, I have found that most recordings do pretty well with the audio set to "Auto", unless you're in an extremely controlled environment.
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Old February 14th, 2007, 03:34 AM   #5
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Quote:
Originally Posted by Dennis Stevens
They said they heard clipping.
Who did, who heard it?
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Old February 16th, 2007, 08:14 PM   #6
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I think you have to be careful who and what people say about your work, the problem could be at their end.
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Old February 16th, 2007, 09:34 PM   #7
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Alot of good info here.I'll try to add a bit.Kits comment seems like it could be your situation.If the mic output is correct for the transmitter , the receiver level should be somewhere mid position to keep it from distortion before it hits your recording device control.Otherwise you may be cranking the level up at one end and down at the other.Kinda like driving your car with your foot to the floor on the gas and riding the brake to control speed.I try to center all controls when starting, then fine adjust from there.
Another thing I do is after mixing the audio , using decent monitors, I run it through a set of cheap speakers to make sure I haven't any distortion from excess freq. or dymacics that the good speakers handle but cheapies don't.
Some TV's have pretty crappy speakers/preamp.
If your building the video for TV broadcast or otherwise, you may want to roll off the low freq. at a minimum 20hz up to 80hz sometimes.
3 other things. Check it yourself,check it yourself,check it yourself.
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Old February 21st, 2007, 04:34 PM   #8
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Audio for DVD

I am also editing a documentary which will be finished to DVD.

My audio is OK from origin, being around -12db.

I am not sure how to finish my audio for DVD. There are interviews and bands playing. The interviews have the audio at a constant level, but the bands have a lot of peak variations.

I am not sure at how much dbs my final audio should be. I am also not sure if I should apply a compressor or a limiter in Soundtrack Pro so that all my audio is around the same level.

I think I should leave my audio levels at around -5 db, and limit it at -1db. But I really dont know if this is OK or not.

I appreciate suggestions.
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Old February 22nd, 2007, 11:42 AM   #9
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Hi Dennis,

There are multiple possibilities.

1) They *think* they hear clipping. Solution: listen to the same tv set in their presence, and have them show you exactly where they hear clipping. Also, make sure you are using the same terminology. While you might know what clipping technically is (= audio levels go above 0dBfs and distort because they are flattened), they might have picked up the word somewhere and use it in the improper sense (don't laugh, I've seen this over and over...).

2) The peak meter on your NLE screen is never accurate. It's a fact of life. It is slower than the actual transients of your audio. You might consider investing in a good PPM meter (RTW or DK Audio e.g.) Now you will now why these are so expensive *grin*.
Try a brickwall limiter on the master fader, set at the level you don't want to exceed (e.g. -10 dBfs). Ensure your gain staging is correct.

3) You hear the clipping on their system too, so there is something wrong on your end. If you have a buddy who is a recording engineer professional, ask him to check out your rig. It could be very simple things.

Hope this helps a bit

Cheers
Arthur
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Old February 22nd, 2007, 11:56 AM   #10
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Only one thing I can add here is that you should always monitor your audio while recording it with a good set of cans.

A meter will show you the level of your audio, but not the quality. If there is distortion due to improper gain staging before the volume knob, you'll be able to dial the knob down to where the meters look fine, but your audio will still be clipped/distorted from earlier in the signal chain.

-gb-
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Old February 23rd, 2007, 12:40 AM   #11
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Quote:
Originally Posted by Jack Smith
Alot of good info here.I'll try to add a bit.Kits comment seems like it could be your situation.If the mic output is correct for the transmitter , the receiver level should be somewhere mid position to keep it from distortion before it hits your recording device control.Otherwise you may be cranking the level up at one end and down at the other.Kinda like driving your car with your foot to the floor on the gas and riding the brake to control speed.I try to center all controls when starting, then fine adjust from there.
Another thing I do is after mixing the audio , using decent monitors, I run it through a set of cheap speakers to make sure I haven't any distortion from excess freq. or dymacics that the good speakers handle but cheapies don't.
Some TV's have pretty crappy speakers/preamp.
Good advice, I believe in the 10:30am to 3:00pm rule, if 12:00pm is the middle point for audio, anytime the audio levels have to be set lower than 10:30am or higher than 3:00pm there might be an audio mismatch somewhere along the way.
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Old February 23rd, 2007, 08:23 AM   #12
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Quote:
Originally Posted by Alessandro Machi
Good advice, I believe in the 10:30am to 3:00pm rule, if 12:00pm is the middle point for audio, anytime the audio levels have to be set lower than 10:30am or higher than 3:00pm there might be an audio mismatch somewhere along the way.
Whats that about 10:30am to 3:00pm???
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Old February 23rd, 2007, 11:42 AM   #13
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Beats me, and while we're at it, what do you mean with an "audio mismatch"?

Cheers
Arthur
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Old February 23rd, 2007, 11:56 AM   #14
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Quote:
Originally Posted by Arthur Kay
Beats me, and while we're at it, what do you mean with an "audio mismatch"?

Cheers
Arthur
If you imagine the mark on the knob of the level control as the hand on a clock, it's pointing at about 7o'clock when it's all the way off and about 5 o'clock when it's full up. The optimum setting is usually in the zone between 1/3 and 3/4 of the way up, or between 10:30 and 3:00 by the clock analogy. Audio mismatch would mean the output of one stage is too high or too low for the input of the next stage in line.
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Old February 23rd, 2007, 12:03 PM   #15
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Quote:
Originally Posted by Greg Boston
Only one thing I can add here is that you should always monitor your audio while recording it with a good set of cans.

A meter will show you the level of your audio, but not the quality. If there is distortion due to improper gain staging before the volume knob, you'll be able to dial the knob down to where the meters look fine, but your audio will still be clipped/distorted from earlier in the signal chain.

-gb-
Excellent point.

I've noticed over the years that if my audio dials have to be set ultra low or ultra high to get an acceptable reading, the odds are that the audio levels are not properly matched throughout the audio set-up. I call that the 10:30 to 3:00 rule (in which the audio dials have a full range of 7 o'clock to 5 o'clock with 12:00 o'clock being the center defaul).
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