From: D & m <>
>
> Im one those who Walter refers in a previous thread
>
> "It could be very easy for this group to become nothing but technical
> discussions. But that would not be very attractive to new folks to
> nature recording. We need to get them hooked before we drop the ton of
> technological bricks on them. You can record well without understanding
> the terminology, though it's easier if you do understand the
> implications of that stuff."
>
> Even after followering to the group for several months now I still
> having a lot of trouble appreciating what is a good mic and how that
> relates to the dollar sign. From recent messages I'm not the only one.
> Some of this is terminology and unfortunitly I can not access the link
> on the groups home page which may help. Then there are varous
> specifacations one reads for example self noise, is very important but
> the difference between a mic with 25dB and 40dB are still figures.
> Something that I could relate to is how much closer am I going to get to
> that bird for the same recording. The some for self noise (how much
> extra hiss I'm going to hear in the background with an extra 10dB ) and
> there is sound to noise ratio. Other specifications such as output
> Impedance and Dynamic Range are just figures.
Unfortunately it's not straight simple answers.
For instance, on "how much extra hiss I'm going to hear in the
background with an extra 10dB". This depends, primarily on the gain
setting you use on your mic input, it's variable. As you increase the
gain, the mic's self noise is amplified right along with the sound you
want. It's generally better to think in terms of the site you might can
record. With 10dB lower self noise you can record a site that's 10dB
quieter and still end up with the same background hiss level. Since in
nature recording we are often dealing with recording quiet sites, self
noise is a limiter on how many sites we can record well. If we try to
record too quiet a site the sounds from the site will sink into the
noise floor of the mic.
The self noise number is determined in testing by comparing it to a
standard 94dB sound level. It's only really valid at that gain setting.
For nature recording we are usually recording quieter sounds, so more gain.
You may note that signal to noise specifications are generally just
another way of saying the same thing. The self noise figure is
subtracted from the 94dB test level.
Incidentally, when we say dBA we mean the test sounds had a
frequency/intensity distribution that paralleled human hearing. One can
also test using a even frequency/intensity distribution, which is
usually what it is when the figure is given in dB. The two numbers may
be quite different.
There's another aspect to self noise. It does not all sound the same.
With some mics it's a nice smooth sound that you hardly notice, with
others it might be a sputtering or crackling sort of sound. Obviously
with the smooth sound you can have it somewhat audible and not bother
the listener, but with some of the others any audibility is undesirable.
At the beginning of this group one of the first discussions was just how
good a self noise figure was needed. While there was no absolute
agreement a figure of 16dBA or less was more or less the conclusion.
Above that figure it was going to often be limiting, below that figure
it would be less of a problem.
Self noise is only one thing of importance. Others are sensitivity,
handling noise, wind sensitivity, humidity and temperature sensitivity.
It's rare that either dynamic range or max sound level is a issue for
mics in nature recording.
> I have looked at a number of sites that has a general advise on tools
> and methods. Also there have been a number of references on what makes
> a good mic in this group but there is hell a lot of messages to read to
> get a grasp of it all. I'm asking the impossible, can there be a set of
> guidelines amongst the group that would make an ideal mic, one that
> would do the job and those that will disappoint you for individual calls
> vs ambiance recordings. There is no need to mention specific makes of
> mics or other additions such as barriers as one needs to get a grasp of
> the basics befor being side tracked down another path. Some one could
> explain in practical terms what the varies specifications are. This
> maybe a useful reference for the home page.
The problem with the concept of a ideal mic is there is no such animal.
A mic that shines for one use may be a dog for another. I tend to think
in a purpose orientation. For instance if I want to record a entire
marsh full of many species of frogs I would use a SASS mic for a overall
recording of the marsh, the ambiance and all the calls together in a
wide view. That's a good purpose for that mic. But, if I wanted to pick
out a individual frog, or small group in the same marsh, I'd use the
Telinga parabolic. Because it's stereo the Telinga will still contain
some ambiance, but will bring out the wanted individual or group. By
aiming at each group I could record the entire marsh piece by piece,
something I do if recording for scientific survey. My different mic
setups are chosen to cover a range of field widths and distances. For
any particular use one or another is going to be ideal.
This is why our response to someone asking for the ideal mic tends to be
to ask what they intend to record.
For picking out individual calls the focus is usually on directionality,
we want to exclude sounds other than the calls we want. Two types of
mics are common here. The parabolic mic has the sharpest directionality,
it will reject the most of the surrounding sounds. And, because of the
reflector it's got extra gain that occurs before the mic. Gain that does
not amplify the mic self noise. A noisier mic can be used in a parabolic
as a result. For those with a limited mic budget who are doing
individual calls the parabolic is the most bang for the buck.
The alternative for individual call directionality is the shotgun mic.
It rejects sound from the side, though not as sharply as a parabolic.
It, however, provides no extra gain before the mic for the caller you
are pointing at. You have to provide that extra gain amplifying the
signal and thus the self noise. For this reason a shotgun mic has to be
very low self noise, and ideally high sensitivity. That combination
makes good shotgun mics for nature recording expensive.
Of course there is a third alternative for individual calls. That's
getting close. That opens up the mic choice. And you can get into things
other than mics. Like Ghillie suits and other stealth methods.
Ambiance adds a different problem. You want to record a soundfield, all
the sounds. You may or may not be doing this in conjunction with
recording individual calls within the soundfield. What this introduces
is that all the quieter parts become important and need to be accurately
recorded. Thus the need to have the lowest self noise in the mics. Which
tends to mean expensive. It also introduces the concept of field size,
you could record the ambiance of a small area all the way up to
everything all around you to all distances (the last for which there is
no ideal mic)
Ambiance also brings in space or physical volume. Which is best done in
stereo. This not only introduces the added cost of a 2nd mic, but the
problems of relative positioning of the mics to accurately portray the
soundfield. Here I can give you a readable reference, "The New Stereo
Soundbook" a good coverage of the techniques that does not get over
technical:
http://www.stereosoundbook.com/
I should note that, although it may seem so, nature recording does not
use the very highest priced mics much. The Sennheiser MKH mics, as high
priced as they are do not compare to others at wallet deflating. Price
is certainly a consideration, but it's easy to end up with a system
where the recorder is far more capable than the mic attached to it. The
mic is the most critical component. There is a lot of focus right now on
high sampling rate uncompressed sound recording with very little notice
that the mics used won't come close to providing the quality of signal
needed. Just recently I saw one person discussing this and he figured
the mics he could afford did not even challenge 16bit 44khz sampling.
For the most part we work with mic designs that were perfected for
analog tape. Putting the word digital on them does not change that.
Walt
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