At 12:26 PM -0500 2/17/05, Walter Knapp wrote:
>From: Rob Danielson <>
>
> > Hi Klas--
>>
>> I agree that people need to understand that the self noise
>>component is fixed.
>
>I'm not so sure I agree with such a statement without a lot of
>qualification. The self noise does get amplified with the rest of the
>signal. Therefore, as you change the gain on the pre, it's level changes
>too.
>
>About what stays fixed is it's relationship to the sound you want. If
>the self noise is 30 dB below the sound you want, and you amplify the
>signal, it will still be 30 dB below the sound you want, but louder.
>
>What we are really wanting to do is keep the self noise below the
>threshold of hearing, or failing that, at least below the threshold of
>awareness. And that's for the final playback volume.
>
>Walt
>
>
Sorry I'm not making myself clear. The relation I hoped to describe
with the phrase "noise component" is that the self noise introduced
by the mic is part of the total signal as a fixed percentage. The
noise introduced by the mic pre, at its current setting, is also a
fixed percentage.
The Rode NT-4 mic has 6.5 dB(A) LESS self noise than the Shure 183
but the NT-4 produces a recording with MORE noise when MD record gain
is set at 23-- which is typical for outdoors. Taking the mic self
noise spec alone can be misleading, especially if one is interested
in recording ambience.
I appreciate Walt's framing of mic self noise in relation to ambient
sound levels because in some situations it is totally irrelevant. I
can set levels for a cardinal at 15' or a snow blower down the block
and play these recordings back without noise becoming a significant
part of the experience.
However, when recording ambience under quiet conditions- mammals
walking through the woods at night, the hush of dusk, the murmurings
of a city at 3am on frigid winter morning-- the noise introduced by
mic/mic pre combination is a very audible component of the
recordings. I'm interested in the details of these spatial events so
when I play these recordings, I'm amplifying the original event 50dB
or more. In contrast, a frog or bird call played over many recordists
speakers might be amplified ~6dB louder during home playback.
Mic/pre Noise plays a very different role in these contrasting
playback situations. Rob D.
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