What caused my clipping!?!?

L

lozampognaro

Member
This past summer I filmed a documentary in Italy about Italian folk music. I shot it by myself and was running and gunning like a madman in 100+ degree heat the whole time. Because of this I needed a simplistic and portable audio system. I chose to use two AT 4051a condenser mics that I plugged directly into the camera to record onto the tape.

I originally thought I would be setting the mics up on a micstand, so I brought a "sawed off" mic stand and two 50ft XLR cables. I began recording on these but was noticing clipping on the high end. I figured that the capsules were getting over loaded and decided to move the mics farther from the instruments. Ultimatly I began mounting the mics directly on top of my camara on the hot shoe in an XY pattern and I got my best results this way but was still getting the clipping. YES i was watching my levels closely and using headphones. However I couldnt hear this problem unless I hooked it up to an external speaker and played back the tape.

Bascially I'm still not really sure how I could have dealt with the problem or what exactly caused it. Italian folk instruments have got to be some of the most difficult to record accoustically. They considt of bagpipes, tambourine and a piercing oboe like instrument. All these instruments are loud and when played together create a lot of sound (bagpipe alone has 5 pipes playing at different pitches plus all the overtones). It was a real challenge to get the sound right while also operating the camera and sweating my ass off.

I think most of the clipping can be taken care of in post with the help of professional sound enginering. But I would really like anyones' ideas as to what was causing my problem. Was it my mics? Is the sound processor in the A1 crappy? Did my leves need to be turned WAY down? Were my mics too close and getting overloaded (I had them pretty far from the instruments)??

EDIT: I SHOT ON XH-A1

Thanks!
 
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Choosing the correct mic for the job then mic placement & setting levels gets the ball rolling, and you tried to do this. The next step is to use gear that is more "pro" with limiters and input attenuation.

The DVX & HVX have fairly nice limiters as far as low cost cameras go. Limiters let the sound get only so loud and then they start clamping down on it and prevent clipping. Limiters as such, are not the same as a Automatic Audio Level Control circuit that is found on many consumer cameras. These circuits cause quiet passages to raise in volume causing hiss and all sorts of unbearable anguish; they should not be used at all.

Cannon A1 camera? I believe does not have a limiter, which would explain the results. Bringing the levels way down is your best bet for a somewhat listenable recording w/o clipping.
 
You don't mention what camera you were using but I doubt you were overloading the mics. So I'm guessing the mic's were overloading the camera's mic Pre's. You said you got distortion on "the high end". Does that mean clipping on loud parts or high frequency's were clipping but others were not? If your problems were feq. dependent then I suspect your camera has a problem. It's too strange that both mic's would be defective in the same way.
 
Thanks for the responses. I was shooting with the Canon XH-A1. It does not have limiters but you can adjust each mic manually. I dont think the problem was caused from the level shooting up and not being suppressed by a limiter. The level would mostly stay constant. when the music was going. A bagpipe only has one volume level. But I would notice the clipping (i think that's what it would be called) when the pipe would hit high notes or if someone would begin singing with the pipe. This would NOT cause the over all level of sound to go up so that I would have to adjust the levels, but it would increase the number of sources of sound that the mics were attemting to capture.

Also one particular instrument that is most similar to what we would consider an oboe would cause me the most problems. Even if I had the level at a good spot and it wasnt too loud in my head phones it could cause a "crackling" sound when I played it back.

Here is an example of the type of music I was recording. the guy to the left of the bagpiper is playing the little instrument that was giving me the most trouble (I didnt film this clip, just found it on youtube):
http://www.youtube.com/watch?v=YFnvTp6gtOQ&feature=related
 
I'll bet if you shot it with a DVX or HVX, limiter engaged, you would not have posted anything here; non issue. Cannon has finally upgraded their crappy audio circuits to a more respectable quality. Those high pitches have more waves per second and I'll bet they also have increased sound pressure dB levels. Also, when someone starts to sing thtat's more signal & the waves can combine and resonate which will increase dB levels. I bet a limiter would have saved the day.
 
Interesting. So then it doesn't have anything to do with the microphones but with A1's internal electronic. Can anyone corroborate this? Has anyone else with an A1 dealt with a similar issue?
 
What this actually sounds like is the compressor freaking out. I have seen this on M ini Disk recorders. You were shooting HD I'm assuming. HD, I assume to make room for the video, uses a compressed audio format like MP3. So your audio goes through the A/D converter and is then compressed into an MPEG 1 layer 2 stream. That compression can get freaked out by things like doppler horn bys and such. I bet bagpipes would set it off also.
The good news is that there isn't much you could have done, the bad news is that this kind of sound will probably cause this kind of problem again. So you might want to consider an outboard recorder for this kind of material.
 
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