At 2:00 AM +0100 2/18/04, Klas Strandberg wrote:
>
>
>Preamp noise / mic noise:
>There are several simple ways to find out, accuratelly enough:
>
>As a reference you can use a radio with fm noise between stations. Put the
>mic at an exact distance from the loudspeaker, set a certain recording lev=
el
>(perhaps - 10 db of your MD, DAT) and make a 30 sec recording of the noise=
,
>then switch the radio off and make a 1 min recording of the "silence", as
>good as you can. It doesn't matter if there is a distant traffic rumble or
>atmo on the recording.
>
>Then do the same proceedure all over, - set the same recording level by
>using the FM radio, but now with the test object connected, (preamp or oth=
er
>mic)
>
>Make a stereo file of the two recordings. Remove all frequencies below 500
>Hz. Equalize the FM radio noise of one channel so that it resembles the
>other channel as much as possible. (Perhaps you have a software frequency
>analyser?)
>
>NOTE: If you can't make the two recordings of FM noise "equal", you can't
>use this method!!
>
>Listen to the "silence" of each channel. This way you will not only hear t=
he
>db-output, but also the characteristics of the noise. Spend money on a
>preamp or other mic if you hear a difference.
Of course, I cranked the mic pre in my test with the specific
interest of _recording the background_. One can also start off with
max mic pre gain and lower it in steps listening for the "sweet spot"
where the most gain with least addition of noise is realized.
Using radio fizz to simulate local hi Hz sources like moving leaves,
grass, running water, insects, radio fizz is clever, but doesn't the
high end in many natural settings drop off so quickly that the noise
from the mic/pre combination quickly rises above them? My specrtral
curves outside are very steep.
>Consider though, that a "distant" rumble may "mask" noise. The two
>recordings may not be too different. And you really have to concentrate on
>the noise itself, unless there is a really big difference. Also consider,
>that even if two mics (pres) may measure the same self-noise, one self-noi=
se
>may be more "scratchy" than the other, and more audible.
As Walt and I discussed a while back, I find the most obtrusive noise
contributed by mic/pre combinations is in the range of 125 to 900Hz.
Lower signal to noise in this range places a sonic haze over the
subtle reflections of the local acoustics/communications. Could this
be a component of your "scratchy" description?
>
>Wayne writes about coloration due to distance, ground reflections and
>general acoustic conditions. This coloration is HUGE!!!
>
>Klas.
>
>At 14:43 2004-02-17 -0800, you wrote:
>>Wayne Brissette, you wrote:
>>
>>>All this recent talk about pre-amp noise and microphone noise has me
>>>wondering about coloration in nature recording. Unless people are using
>>>omni microphones (and recent posting suggest people are using hypers and
>>>shotguns) then there will be some frequency bumps and drops. This in
>>>addition to some of the preamps talked about leads me to believe that
>>>there will be some alteration in the sound. As a very rank amateur in
>>>this field (although I have done my time in a studio), I'm wondering if
>>>this matters much or since most people are trying to capture a specific
>>>species of animal this doesn't play that big of a role. Anyhow, I'm
>>>curious how all this plays into this field.
>>
>>For me, frequency response is the same for nature recording as it is
>>for music recording: I want the recording system to be as flat as
>>possible.
>>
>>Once I've working with it in the studio, however, I may filter and
>>equalize the hell out of it to bring out what I need, or to make it
>>sound more natural! Like a photograph, a recording is an illusion of
>>reality, and what's right is what makes the illusion you want.
>>
> >-Dan Dugan
>
What is increasingly interesting to me about this process of partial
"recovery" of mic/pre etc. prejudice through equalization is how
much more aware of the influences of the physical surroundings I
become-- like comb filtering along the ground, or the echo from a
wall of trees surprisingly far away. The practice truly does require
getting to understand the "real" better.
It seems like my work is often to lessen the resonance(s) of a
location so that the lower level phenomena may be audible. This is
contrary to experience in the field, where local resonance is often
the harbinger of overtones, edges and access to greater details.
Rob D.
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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