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From: rcd@opus.UUCP
Newsgroups: net.audio
Subject: Fletcher-Munson curves obsolete?
Message-ID: <273@opus.UUCP>
Date: Sat, 24-Mar-84 03:49:11 EST
Article-I.D.: opus.273
Posted: Sat Mar 24 03:49:11 1984
Date-Received: Sun, 25-Mar-84 13:38:32 EST
Organization: NBI, Boulder
Lines: 36

<+>
I have a manual for a piece of audio equipment which criticizes loudness
compensation circuits in preamps "...because they are based on the obsolete
Fletcher-Munson curves and produce excessive mid-bass boost..."

[Background, for general interest:  The "Fletcher-Munson" curves are a
presentation of empirical data which show curves of equal perceived
loudness on a plot of sound pressure level (acoustic power) vs. frequency.
(Say wha?...)  For example, using a 1KHz reference they show that a 60 dB
sound at 1KHz sounds as loud as roughly 70 dB at 100 Hz or as 57 dB at
3KHz - thus one constant-loudness curve passes through these three points.
Each curve has a characteristic shape which shows that the ear is most
sensitive around 3KHz and loses sensitivity at higher and lower frequencies
according to a particular pattern.  The family of curves shows how the
differential sensitivity to frequencies changes with sound level, becoming
less pronounced at higher levels.  End of digression.]

Now the question:  If these curves are obsolete, can someone please tell me
WHY they are obsolete - is the data wrong, was it presented wrong, or has
it been consistently misinterpreted?

Here's the reason I'm asking - I'm wondering if people have built "loudness
controls" with contours which mirror a F-M curve for some particular
loudness level.  If so, they've obviously misinterpreted the data; the
control contour should be based on the variation in shape of the F-M curves
for different levels.  Example:  If you have music recorded at a typical
90dB SPL but you want to play it back at a typical 60dB level, the contour
you want is one which will boost bass and treble so that the system
response (system = loudness control + ear) has the shape of the 90 dB curve
at 60 dB - NOT one which will give FLAT system (control+ear) response at 60
dB.
On the other hand, if there is something fundamentally wrong with the F-M
data, I'd like to make some careful notes about it in my copy of Beranek's
"Acoustics" book.
-- 
{hao,ucbvax,allegra}!nbires!rcd