Clipping/Distortion using Videomic that didn't previously happen in same situation at DVinfo.net

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Old August 18th, 2006, 03:40 PM   #1
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Clipping/Distortion using Videomic that didn't previously happen in same situation

Hi

Had an audio problem i've not come across before and thought i'd bounce it off you knowledgeable people:

Taped a live band on 2 different days in (lmost.) identical cricumstances / equipment / settings and got two very differetn audio results, so i hope someone can chip in with some theory/comments as to why.

Camera was HC1000 + Rode Videomic and i was using Auto audio levels for the simple reason that i have filmed the SAME band at the exact SAME location with the SAME equipment and even standing in the SAME place and got really excellent sound before, but this time, i got a lot of distortion on the sound, am certain the mic was overloading the HC1000's preamps..

Now I'm 99% sure the band were using identical volume levels on their amps and they were playing the same set of songs even, so the question is WHY did i get excellent audio the 1st time and distorted audio the 2nd time?

- I've thought about it and the ONLY difference is that the 2nd time i was using the Rode Deadcat windshield (as the location is half indoors/half outdoors and there was a bit of wind so i was being cautious not to get any wind noise), AND i decided NOT to use the low-cut filter the 2nd time. (to get a slightly more bass-heavy audio track).

So my theory is this:
- Did leaving the low-cut filter filter OFF the 2nd-time (and maybe using the Deadcat) have caused the overloaded audio? If the majority of the output from the band's amps/speakers was fairly bass-heavy then it makes sense that the low-cut filter used the first time may have taken the levels down just enough to not cause clipping & distortion. Use of the Deadcat the 2nd time also would cut the high-frequencies a bit and this would also help create a more bass-biased sound being picked up by the mic.

Has anyone else had this happen to them on the Videomic (which i do know is a hot mic and a bit borderline on overloading) or any similar shotgun mic?

- I didn't use manual levels as the band was playing soft tracks and more rocky tracks and i wanted also to pick up the chit-chat with the audience inbetween songs and to do that with Manual levels would have meant riding them more than i wanted to and would have a bit tricky to do that and get the images right too.

Phrased a different way, if you had two "identical" shotguns and one was designed to give a more treble-oriented sound (maybe ME64-like - you know what i mean) and one was designed to give a more bassy EQ, then is it possible that if they were identically sensitive that the "treble-oriented" mic would not produce clipping like the bassy-mic ? (when taping a band using speakers that may have rather bigger woofers than tweeters...)
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Old August 18th, 2006, 06:07 PM   #2
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It was almost certainly the lack of the low-cut filter.

When mastering a CD for maximum levels, the technique is to us a multi-band compressor. In generally, they just cut the lows to keep the signal from clipping. The highs are much less likely to overload the system.

Think about it. When recording voice, it tends to overload on the "P"s (LF), rather than the "S"s (HF).

-JF
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Old August 18th, 2006, 08:08 PM   #3
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Quote:
Originally Posted by Jon Fairhurst
The highs are much less likely to overload the system.

Think about it. When recording voice, it tends to overload on the "P"s (LF), rather than the "S"s (HF).

-JF
Thanks Jon - yes this was my thought process too that it was the lack of low-cut filter giving greater low-frequency response. I think i have learnt my lesson on that and will keep low-cut filter on when filming bands using amps and biggish speakers.

- I admit I was quite shocked how bad it was compared to the first time when i used the LCF!
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Old August 19th, 2006, 07:12 AM   #4
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This seems a logical explanation. You can easily confirm it by looking at the waveform in whichever NLE/DAW you use.
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Old August 19th, 2006, 08:10 AM   #5
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Checked the battery? Does the battery have a "fade" effect? When switching the roll-off maybe this causes less more battery drain? And if the battery is under par .. maybe? Just check voltage and change battery and knock that variable out.
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Old August 19th, 2006, 12:10 PM   #6
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Quote:
Originally Posted by Graham Bernard
Checked the battery? Does the battery have a "fade" effect? When switching the roll-off maybe this causes less more battery drain? And if the battery is under par .. maybe? Just check voltage and change battery and knock that variable out.
Thanks Graham.
Haven't got voltmeter/multimeter with me as am holidaying.
9v batt is pretty new, (i'm on my 3rd or 4th one with the Videomic...) so am pretty sure it's not the batt.

Band is on again today i think, so i'll try it again with LCF switched in AND if i can get away with it, the Deadcat off (as that will itself filte any high frequencies and therefore make the whole track a bit more bassy).
I'll buy a new batt too, and swap them in and out to see if any differernce. Rode has LED that goes red when the battery is fading and i think it's fairly conservative as its gone red before and i've kept shooting and sound has been spot-on. LED is still full green at the moment.

thanks for the input geezers! top stuff, appreciate it.
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