Posted by: "Donald Berk"
>
> Walt, thanks for an absolutely clear and concise comparison. I really
> can't contribute to this forum yet but hope to repay the generosity as
> I gain experience. I do have some experience with active noise
> cancellation (ANR) in aviation headsets and am wondering such circuits
> are used in canceling noise in nature recording applications.
Start by noticing there are major classifications of noise.
First is sound that's in the environment but unwanted. Planes flying
over, cars and trucks, dogs barking, people talking and so on. This is
the type of noise that ANR is designed to reduce. It does so by using a
mic to pick it up and then plays it back inverted.
The problem is the same mic will also be picking up the wanted noise.
The wanted sounds come out of the environment, not from a recording or
such like. So ANR will cut down the sound you want too.
Environmental noise like this is a huge problem. One airliner anywhere
above the horizon can ruin a recording. Same with trucks miles away and
so on. For most beginners in nature recording this is the biggest
surprise, just how much noise there is. Our ears are very good at
singling out the sounds we want, mics make no such distinction. One can
help our ears by recording in stereo as one of the major ways we filter
out unwanted sounds is directional.
A second type of noise is that produced by the mic or other parts of the
electronic equipment within the electronic signal. Good design can
minimize but not eliminate this. In nature recording we are often
recording very faint sounds and the mic self noise and so on will
interfere. The quieter the environment you are recording in, the better
the mic has to be.
There are natural environments quiet enough that even the quietest mic
the self noise will intrude. Best you can do in this situation is choose
a mic that has the least intrusive self noise because the listener will
hear it. Some mics sputter and crackle in their self noise, others can
be a nice smooth paaaaahhhhh sound. It should be obvious which is
preferable.
ANR is going to be of no help for mic self noise.
There is actually still another class of noise. Condensor mics work by
maintaining a charge between the diaphragm and a backing plate. That
charge is humidity sensitive. Many mics simply cannot be used for nature
recording due to this sensitivity. That includes high end mics. As they
are exposed to moisture they get noisier and noisier until that
overwhelms any useful signal. With some mics it's just a matter of
seconds. The mics are not generally damaged and will work again once in
a drier environment, but that does not help for nature recording.
This area is one where the Sennheiser MKH series has a big advantage.
Instead of a high voltage charge the MKH use a low voltage RF charge and
oscillator system to pick up the sound. (similar to FM radio) They are
much more immune to moisture as a result.
Walt
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