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Audio peaking problem

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Taku Suzuki
Audio peaking problem
on May 27, 2010 at 2:06:42 am

I wonder if you can help me with this.

I have to say I have huge gaps in my knowledge of sound recording but naturally need to deal with audio whenever Im shooting assignments.

My question is regarding audio that "peaks" although it was recorded on camera at a reasonably low level.
By "peaking" I mean recorded audio that sounds "broken", not any different than audio that peaks because it has gone through the roof (0db.)
To give an example, I have recorded loud laughter that when levels were set nowhere near the peaking point (the red bit in the camera audio meter). Yet when I listened to it, it was "clipped" and peaking.

The same has happened at numerous live music recordings, particularly at loud music events with speakers all over the stage, no matter how low I set my levels, the sound "breaks".
I only have this problem with amplified loud music or laughter etc. Regular dialogue etc. sounds just fine.

Could this be because my mic is broken or is there something very simple that I haven't taken into account? And how would I know whether my microphone is broken or not?
Or could it have something to do with the microphone's frequency range?
(It seems as if bass sounds often come out as "broken")
In the dark here!

I'm recording on a Sennheiser MKH-416 straight into HVR-Z1


Thanks alot,





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Jordan Wolf
Re: Audio peaking problem
on May 27, 2010 at 7:35:02 am

"By 'peaking' I mean recorded audio that sounds 'broken', not any different than audio that peaks because it has gone through the roof (0db.)
To give an example, I have recorded loud laughter that when levels were set nowhere near the peaking point (the red bit in the camera audio meter). Yet when I listened to it, it was 'clipped' and peaking.

The same has happened at numerous live music recordings, particularly at loud music events with speakers all over the stage, no matter how low I set my levels, the sound "breaks".
I only have this problem with amplified loud music or laughter etc. Regular dialogue etc. sounds just fine."

Well, there are probably a few things at play here:

1. Level Meters - the meters on which you are viewing your signal levels have certain characteristics that make them better (or worse) for certain types of material. This response is called the ballistics of the meter. Certain meters have a quicker response, and therefore are more suited to peak and/or instantaneous levels (think drum hits). Other meters display an average of the signal level and are better for seeing what the overall signal is doing (better for monitoring multiple sources since they can combine oddly, etc.). And there are still others that combine these two types (for better of worse) and allow for simultaneous measurements of peak and average levels.

2. Microphone Diaphragm vs. Distance from Source - It is possible to overload the active circuitry in condenser microphones when the part of the microphone that changes the acoustic energy (sound waves) into electrical voltage produces too large of a voltage for that circuitry. Since the MKH416 is both a shotgun AND a condenser microphone, it may be overloaded more easily than a dynamic, cardioid microphone (think Shure SM58), especially if it is located too close to a loud sound source. The usual way this is mitigated is by use of a "pad" that goes in-between the diaphragm and the circuitry.


"Could this be because my mic is broken or is there something very simple that I haven't taken into account? And how would I know whether my microphone is broken or not?
Or could it have something to do with the microphone's frequency range?
(It seems as if bass sounds often come out as 'broken')"

Again, it is possible that there is a loose component in your microphone. Everything oscillates/resonates (read: vibrates) at a certain frequency or set of frequencies and, if your source material is producing frequencies that cause parts of your mic to vibrate, you may notice distortion and/or clipping.

It should be noted that there are differences in the terms you used:

Clipping refers to the actual distortion that is heard when an audio signal cannot be accurately reproduced by the gear through which it is passing. Peaking refers to the warning lights or signals used to tell the operator "be careful, I close to clipping/overload!".

I hope all that helps you and doesn't confuse you. If there are any questions, feel free to ask them and we'll be more-than-happy to help.


Wolf
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Ty Ford
Re: Audio peaking problem
on May 27, 2010 at 5:00:42 pm

Hello Taku and welcome to the Cow Audio Forum,

In addition to Wolf's excellent tutorial, I'll add the following.

The 416 is a fairly sensitive mic. I have seen such mics overload camera mic inputs when in loud environments. I suggest that you try a good mixer between the mic and camera and see what happens. The limiters and level controls in the mixer may be able to tame the 416 so you'll be able to use it with the HVR-Z1.

My suggestion would be a Sound Devices 302. If you don't want to buy one, rent one for a few days and see if that solves your problem.

Regards,

Ty Ford


Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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John Fishback
Re: Audio peaking problem
on May 28, 2010 at 9:32:47 pm

To add to the above explanations, often there are amplifier stages (pre-amps) that come before the amplifier you can adjust with the dial on your camera. Those can be overloaded and clip, and since that happens before the amp you can adjust, it's still distorted regardless where the meter reads. It is similar to what Jordan explained about the internal mic clipping. You can fight this by placing a pad (it's an in-line device which reduces the audio level by 10, 20, 30 db) in the line before you plug into the camera. Ty's suggestion of using a mixer like the SD-302 is a good one since you can use the mixer's functions to do the same thing - control the level of the audio reaching the camera. It also has excellent limiters that do the same kind of thing - prevent audio from going over a certain threshold point.

John

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Richard Crowley
Re: Audio peaking problem
on May 29, 2010 at 2:58:11 pm

Have you looked at the waveform in a computer editing program? It is possible that you really are clipping (reaching 0dBFS) but the peaks are too fast for your metering indicators.

Can you test the phenomenon with a different microphone? As Mr. Ford observed, it is possible that the clipping is happening elsewhere.


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