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Klarinet Archive - Posting 000221.txt from 2001/02

From: Tony@-----.uk (Tony Pay)
Subj: [kl] Organs and combination tones
Date: Wed, 7 Feb 2001 12:50:06 -0500

On Wed, 07 Feb 2001 06:50:09 -0500, bhausmann1@-----.com said:

> At 08:20 PM 2/6/2001 -0800, William Wright wrote:

> > So far as I know, the word "hear" is very important because (so far
> > as I have read) a difference tone is manufactured by flesh in the
> > human ear, not by interference or summation of sound waves outside
> > of the ear. (See Arhur Benade, "Horns, Strings, and Harmony, Chapter
> > IV, pg. 80+ in the Dover paperback edition.)

> > I don't think that the insides of a tuner manufacture a difference
> > tone, and therefore the tuner won't "hear" a difference tone.....
> > but I could be wrong.

and later:

> > ....in other words, a difference tone is not the same mechanism ---
> > is not produced the same way --- as the 'beats' that we use to
> > verify whether two instruments are in tune with each other. Benade
> > is quite firm about this, and he discusses this confusion in both of
> > his books.

> You may be misreading Benade or something, but I don't think things
> like wall-shaking resultant bass organ notes would work if summation
> of sound waves was not purely a matter of physics. Nor would standing
> waves cause any problems. A difference tone does not need to be
> manufactured; it exists in the air, as surely as two pebbles dropped
> in a pond will cause interfering waves in the water.

This subject is quite complicated. To the degree I understand it,
difference tones of frequency (f1 - f2), (as well as other less strong
combination tones of frequencies (2f1 - f2) and (3f1 - 2f2)) are
perceived because of the non-linear response of parts of our ear
(thought to be the cochlea, though not the eardrum itself) to the
acoustical signal. "They are not present in the original sound
stimulus." (Roederer, Introduction to the Physics and Psychophysics of
Music.)

The 'organ' effect mentioned by Grant, which Roederer says is called the
"periodicity pitch, subjective pitch, residue tone or virtual pitch" is
even more removed from the physical stimulus, occurring at low
intensities, and perceivable even if the two tones are fed into separate
ears (Houtsma and Goldstein, 1972). Thus it "must be the result of
neural processing at a higher level."

"...repetition rate detection [of the fundamental frequency of the
combined waveform] has been used in music for many centuries (and
wrongly attributed to a combination tone effect). For instance, since
the end of the 16th century, many organs include a stop (the "5 1/3 -
foot fifth") composed of pipes sounding a fifth higher than the pitch of
the written note actually played. The purpose is to stimulate or
reinforce the bass one octave below the written note (ie, to reinforce
the 16' sound of the organ). Of even older usage is the 10 2/3 - foot
fifth in the pedals, which, in combination with 16' stops, simulates or
reinforces the 32' bass (two octaves below the written note)....this
tone is called the *missing fundamental*.

Tony
--
_________ Tony Pay
|ony:-) 79 Southmoor Rd Tony@-----.uk
| |ay Oxford OX2 6RE GMN artist: http://www.gmn.com
tel/fax 01865 553339

.... When everything's coming your way, you're in the wrong lane.

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