I'm not sure if I've understood all this, but if weighting is critical to k=
nowing what a noise figure will mean for a particular application, wouldn't=
it be better for manufacturers to abandon the quest for a single noise fig=
ure, and supply graphs of noise instead? Or would that make it too hard to =
sell equipment, with the public unable to decide how to compare graphs?=0D
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Peter Shute=0D
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Sent using BlackBerry=0D
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From: =0D
To: =0D
Sent: Mon Dec 24 11:06:01 2012=0D
Subject: Re: Summary: [Nature Recordists] Re: EIN values and bits and peaks=
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> I agree; the 5 dB figure may apply to urban interior noise, which=0D
> has a lot of traffic rumble.=0D
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The noise figures which we are discussing as "excess noise" are=0D
relative to the fundamental thermal noise of the air. This rises at=0D
the rate of 3dB per octave so, in comparison, low frequency noise is=0D
much greater than low frequency thermal noise. Fortunately our ears=0D
are less sensitive to LF at low levels.=0D
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The thermal noise level from 0Hz to 1kHz is 12dB lower than the=0D
thermal noise from 0Hz to 16kHz. I'll let someone else integrate the=0D
noise under a A-weighting curve. :-) White noise energy is constant=0D
over the same bandwidth, say over a range of 1kHz, but thermal noise=0D
energy rises in proportion with frequency, hence the 3dB per octave=0D
figure. (Why is it not 6dB per octave?)=0D
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This is why weighting is important in all noise measurements. I=0D
haven't concentrated on the source of the 5dB figure but this is=0D
probabably about right with A weighting.=0D
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Going back to a related subject, adding noise at -4dB to a signal at=0D
0dB raises the level by 1dB, which is just about what we could detect=0D
on a meter. However to the ear, adding hiss to a rumble will be very=0D
noticeable and this is only one instance when the theory breaks down.=0D
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David=0D
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David Brinicombe=0D
North Devon, UK=0D
Cogito cogito ergo cogito sum - Ambrose Bierce=0D
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