New member -- mic overload question
 

Hello, all --

New member here, with a new VX2100.

My first shoot involved a very loud rock concert and I used the VX2100 internal mics. The audio was distorted, and I think it might be related to the fact the house sound was pushing 120 dBA during the concert.

Does anyone have any idea what the internal mics are spec'd at for max SPL? I've looked all over and can't seem to find that info.

An earlier set at the same concert recorded fine, but it was definitely a quieter show (around 95 dBA levels). I used manual setting at all times, and kept the meter well below the red.

For the future, I'd like to figure out how I can deal with recording these kinds of audio levels, either using the internal mics or some suitable external stereo mic.

Been reading the forum for awhile and have found it very informative; but I don't recall seeing this topic discussed before.

Any help would be much appreciated!

Thanks,

Larry

Well.. If you have record these concerts for the venue or band, pick up a wireless mic kit and get the transmitter to the sound guy and have him output you the master out to the transmitter.. Good clean sound..:)

As for picking up sound and crowd at a AC/DC style loudness.. I have never had any problems turning the gain down, infact I have used AGC as well in loud loud areas because of the limiter built in. You could also pick up a mobile pre-amp for your mic that has some more settings and limiters. I use a Art Tube pre-amp sometimes with OPL it works really well and gives it a nice sound too..

Sony's limiter works well I find, but at those sound pressure levels you're not only doing your hearing no good, you're also overloading the microphone capsules themselves. Once they hit the end-stops the limiter can't help you.

tom.

Thanks for the good advice, guys!

I was actually surprised to see this much difference in sheer volume between the two acts (Radio Shack meter showed 95 dbA and 120 dbA).

The whole session was very impromptu -- I was onsite for something else and was asked to do some volunteer work. In the past, when I had the gear and the time to coordinate, I have used an outboard XLR adapter to patch in a soundboard feed (mono) and a high SPL condenser for ambience. Didn't have access to them this time, though, and tried to go with the internal mics (watching the meters like a hawk!)

I'm theorizing that what happened was that, as Tom speculated, the mic capsules themselves were overdriven because I kept the meters well below midrange.

I was wearing a set of Sony 7506 headphones at the time, which saved my ears some ringing, but really didn't do me much good in hearing the distortion in real time (the earcups don't really isolate enough).

In the future, I will definitely prepare better, equipment wise! I was still curious as to how I might find out what the VX2100 capsules are spec'd at -- mostly to validate my theory about what went wrong. Weeks of websearching have been fruitless, and I'm about to chalk it all up to experience.

Many thanks for your thoughts and suggestions!

Larry

This is a common misconception. The fact is that adjusting for good meter readings does not affect the size of the signal voltage appearing at the the input to the cam's audio preamps. The meter readings indicate recording levels, not input levels. It's more likely the mic's signal was just too darned strong under 120 dB sound pressure than it is that the mic's max SPL is lower than 120 dB.

Other higher end camcorders have built in mic attenuation options for use in loud environments. I was surprised not to find any such option in my VX2100. Anyway, if you use an external mic you will have the option to add an in line attenuator between it and the cam.

I'd almost bet the stock microphones won't handle 120 dB. It takes a fair microphone to handle that kind of level. The ever popular Sennheiser (and most other) shotguns won't do well either.

I use a very rugged microphone for those types of events, an AT SM81C. It handles 132 dB with no problems. Even will record a Barret 50 cal rifle with accuracy.

You may be right, Mike. From looking at cardioids lately, most of which cruise in the 130-145 dB range. I was thinking of all mics as being more robust. On the other hand, we're not talking about shotguns either--they tend to have the lowest max SPL.

Anyway, it's probably a good bet that the relatively cheap stereo mic on even a good cam like the VX2100 can't handle 120 dB. But cam mics tend to be very sensitive, so my own bet would still be that loud sounds causes clipping at the preamp before the max SPL of the mic is hit.

Whether or not that's true, I think you'd agree that the solution for Larry is still an external mic that can handle the sound levels, and an in line attenuator if needed (which is likely).

Many thanks to all for your ideas and suggestions!

I agree that the first thing to do is to get control of that level going into the preamps, and in the VX2100, that's only possible (without mods, of course) by utilizing external mics.

Even finding and using mics with high SPL ratings won't do me any good unless I can add attenuation where it's needed, so I'll probably just keep using my XLR-Pro (which I didn't have for this recording) for providing both the interface and the variable attenuation I need, but also pick up a couple mics that I know won't become the limiting factor.

To round out this package, I think I'll need to find some headphones with really good isolation (vice the Sony 7506) so I can actually hear what I'm recording! Live and learn....

Again, thanks for your excellent advice and insights.

Larry

interesting info here...
for headphones that isolate, i recommend the shure e2c
one of the cheapest in-ear phones that really isolate
use it on the mrt [subway], blocks out most of the noise [train noise, loud annoucements, crying babies]