Klarinet Archive - Posting 000148.txt from 2002/11

From: "William Semple" <wsemple@-----.com>
Subj: Re: [kl] dB (was tuners)
Date: Sun, 3 Nov 2002 01:42:17 -0500

Along these lines, to what is the variation in clarinet sound attributable?

----- Original Message -----
From: "Jeremy Yager" <bomber@-----.com>
Subject: [kl] dB (was tuners)

>
> To expand on Mark C.'s arguement:
>
> The dB scale is a logarithmic scale--it can represent great changes in
> values in a given context without having huge numbers (or exceedingly
small
> ones).
>
> The human ear percieves sound energy on a logarithmic scale--making the dB
> ideal for describing human hearing. This is why you can play a stereo (or
a
> clarinet) at a given volume, and adding a second acoustically identical
> source (another identical stereo or clarinet) and it will not sound much
> louder. There is actually twice the energy present, but since your ear
> hears on a logarithmic scale, it does not sound significantly louder as
> 'twice' on a log scale is very little difference--3dB, as stated before.
> Think of the 120dB jet engine and the 60dB conversation that most folks
are
> familiar with.
>
> The only difference between that and dB in the hands of recording
engineers
> (and electricals, too) is the definition of the baseline. On the scale
used
> by hearing health folks (and most people are familiar with), 0dB is nearly
> perfect silence--almost no sound energy, yielding values >0 for any
audible
> sound.
>
> When used by recording engineers, 0dB (unity gain) is different--recording
> equipment systems (IIRC) are defined to be the ideal recording level, and
> consistantly setting the equipment to record at >0 dB levels can result in
> distortion in the loud sections, and recording levels <<0dB, system noise
> (i.e. tape hiss) becomes a problem.
>
> The dB scale can actually be used with any baseline--it is a purely
relative
> scale--you can sensibly say that one signal is at -10dB compared to
another.
> What Dr. Pyne seems to have done is set 0dB to the RMS amplitude of the
> fundamental frequency, and all of the harmonics are merely given in
relation
> to the fundemental--they are all less than the fundamental, so the dB
values
> are all negative. RMS is 'Root Mean Square'. The average value of a pure
> acoustic signal is 0, and thus meaningless, where RMS gives a positive
value
> in all cases, and thus better describes how much energy is in a signal
(the
> harmonic, for example) of interest.
>
> ----- Original Message -----
> From: "Mark Charette" <charette@-----.org>
> To: <klarinet@-----.org>
> Sent: Saturday, November 02, 2002 11:59 PM
> Subject: RE: [kl] Tuners
>
>
> >
> > Perhaps someone else here does?
> >
> > ---
> > You need to read carefully. The scale is dbVrms, where 0 db references
the
> > microphone nominal output. 0 db is just a reference level.
> >
> > If you also check carefully, you will find that some even partials are
at
> a
> > higher level than neighboring odd partials.
> >
> > "1/2" or "3/8" are irrelevant fractions on a log scale ... the whole
idea
> of
> > using decibels and log scales is to amplify small differences. A 3 db
> > difference mean twice the power, a 10 db difference 10 times the power.
A
> 40
> > db difference (as in the 1st chart) means a 10,000 times difference.
> >
> > In a different type of scenario, and extremely simplified, if a trumpet
> puts
> > out a maximum 90 db sound level and a clarinet a maximum 70 db sound
> level,
> > you'd need 100 clarinets to equal the sound level of one trumpet ...
> >
> > Mark C.
> >
> >
> >
> >
> > ---------------------------------------------------------------------
> >
> >
>
>
>
> ---------------------------------------------------------------------
>

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