bbystrek wrote:
>
> Does anyone have any experience with the Audio Technica AT822 stereo
> condenser mic? How does it stack up against other mics in terms of
> background noise? It's the only mic I own and I don't really have
> much perspective. I was pleased with the results recording frogs and
> various water sounds this past spring. It seems a little tricker to
> capture lower level sounds like a meadow of insects. Close miking
> helps improve signal relative to noise, but this can also throw
> things out of perspective where I'm really trying to capture a
> broader image.
Your experience is similar to what I've found my Sony MS 957's can do.
They have a fairly decent noise floor, but the reach is not that great.
I figure them at 50' or less for good stuff. And for quiet calls, much
closer. Their noise floor does not allow much amplification. I use the
MS 957's mostly for bad weather situations as they can be protected
fairly easily compared to my more usual parabolic.
Picking up a good ambient field with mics of short reach is a problem.
Bernie recommends a approach of recording several locations and mixing
to do it, and this seems like one of the better ways if you can get to
all you need to. I deal with swamps a lot in my frogcall work, so
getting close to all parts can be a real expedition even if it is
doable. I like the field I get from the Telinga DAT Stereo parabolic
setup and that can be done from one location.
> Datasheet: http://www.audiotechnica.com/prodpro/profiles/AT822.html
>
> Open Circuit Sensitivity: -45 dB (5.6 mV) re 1V at 1 Pa
> Signal to Noise Ratio: 70 dB, 1 kHz at 1 Pa
>
> Reading various manufacturers datasheets and app notes, it appears
> that quiet recordings at low SPLs are related to both Sensitivity and
> SNR. How does one compare two mics, when neither value is equal? Is
> it always subjective?
Signal to noise ratio is often against 96dBA, so will give you a
absolute noise floor for the mic. For instance a good estimate of the
AT822 would be that it's inherent noise is equivalent to 96-70 or 26dB.
That's only a estimate remember, as mics vary quite a bit under
different conditions. So, the mic will drown out any environment that's
at 26dB or below, real quiet places. But it will be noticeable well
above that as it will restrict the dynamic range from your environment.
Say you are out where the area is 46dB, not a uncommon level in natural
areas, then the usable signal will have a dynamic range of 20dB, and you
will certainly hear the mics noise in the quieter parts. And any
amplification raises that noise floor in absolute sound level, which can
quickly overwhelm anything unless the mic is very low noise. Anyway
that's a simplistic explanation that does not take into account mic sensiti=
vity.
Obviously sensitivity does help in that it can raise that ratio
sometimes. But for quiet nature recording, that noise floor is the one
that's more noticeable. Note that the actual dynamic range we deal with
in nature recording is usually not all that high. Even with loud frogs
fairly close I'll rarely measure above 90dB peaks with my noise meter,
then when you account for the noise floor of the mic that might be a max
dynamic range of 70 or 80 dB at best. Most real situations are half that
or even less.
Manufacturers and their specifications usually assume that you are
recording relatively loud noises. Performance on quiet noises may or may
not relate. And in addition, each manufacturer seems to test mics
differently and choose different specs, so it's hard to get more than a
general idea from mic specs if trying to compare. I usually try to
estimate how noisy a mic is from the specs and only pay mild attention
to the sensitivity. If there's a frequency response curve I like to look
at that too.
> Another reason I'm asking about noise - I'm thinking of getting into
> one of the more robust stereo imaging techniques like M-S or
> boundry.
To do these well does require a fair investment in mics. Worth a bunch
of study. The group archives have a lot on this sort of thing,
particularly discussions of the SASS setup and how to modify it. I'm in
the middle of building a modified SASS.
Not many have the figure 8 mics necessary for M-S. I've the mics and
expect to begin recording some in M-S by next year. Once I get
suspensions and windscreens built.
Walt
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