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Re: effect of mic sensitivity

Subject: Re: effect of mic sensitivity
From: "Eric Benjamin" ericbenjamin2
Date: Sun Feb 24, 2008 3:11 pm ((PST))
Oryoki wrote:
> Let's say the sensitivity of Mic A is rated at 30 mV/Pa, and mic B is
> rated at 15 mV/Pa
and
> will the recording of a reference sound made with Mic
> A appear to the listener to be twice as loud as the recording of the
> same reference sound made with Mic B?
or
> will the recording made with Mic A appear
> to the listener to be only slightly louder than the recording made
> with Mic B?

When you say 'loudness' in this way, then I assume that I assume that you
are referring to the perception of loudness.  The perception of loudness ha=
s
been studied for more than 100 years and there is still a good deal to be
learned, but it is widely held to be true that a change in level (what is
measured by a meter) of about 10 dB is perceived to be a change in loudness=

(what you hear) of about a factor of two.  These sorts of things are
quantified simply by exposing a large number of test subjects to a variety=

of levels of sounds, and asking them the question: How much louder is A tha=
n
B?

The above relationship holds relatively true for sounds at around mid-range=

levels (say, the level of conversational speech), but it deviates at very
low and very high levels.  We'll skip the very high level problem, and just=

concentrate on low levels since it probably applies more to nature
recording.  Assume that I present you with two sounds, one just slightly
below your threshold of hearing, and one 6 dB (twice the level) greater tha=
n
the first sound.  Then I ask you to rate the relative loudness.  Well, you=

will say that the second sound is a great deal louder than the first sound.=

After all, you couldn't even hear the first sound!

For this reason the growth of loudness at low levels is considered to be
steeper (it gets louder, faster, with increasing level) than at mid-range
levels.  And this is important for nature recordings.  Because we tend to
play back the recordings of nature sounds at higher levels than they
occurred in nature, which means that the growth of loudness curve has a
different slope than it did when you heard the sound in nature.  That means=

that the dynamic range of the reproduced sounds is in some sense less than=

it was for natural hearing.

There are other effects that affect our perception of low-level reproduced=

sound, like the fact that the threshold of hearing at low frequencies is
much higher (for example, 76 dB SPL at 20 Hz vs. -4 dB SPL at 1 kHz) than i=
t
is at middle frequencies.  So reproducing a recorded sound just a little
louder than it was in nature can bring out low- and high-frequencies
components in the sound that were inaudible in the original event.

So the answer to your questions is: It depends on the reproduction level.
But for mid-level sounds you will probably judge 'B' to be nearly twice as=

loud as 'A'.

Eric





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