Klarinet Archive - Posting 000453.txt from 1998/01
From: George Kidder <gkidder@-----.edu> Subj: Re: tuning and articulation Date: Fri, 9 Jan 1998 14:27:46 -0500
>Date: Thu, 08 Jan 1998 11:48:04 -0600
>From: James Sclater <Sclater@-----.edu>
>Subject: tuning and articulation
>
>Recently, a friend and I tried out some new clarinets. We were using a tuner
>to check the notes on these new instruments. I noticed that when I started a
>note, the pitch would drop (settle) slightly after a second or so. Yet, when I
>approached the same note from another note, the pitch was at the settled
>pitch. My friend said this happens to him all the time. Is there something
>about the onset of air which causes the pitch to be slightly higher for a
>moment, or is it, as I suspect, just poor breath control? Anyone out there
>had similar experiences?
>
>Jim Sclater
I can't lay my hands on the reference, but I have read somewhere an
explanations which seems to me (as a physiologist) to make sense. Inspired
(room) air contains about 20% oxygen and less than 0.1% carbon dioxide; the
balance is mostly nitrogen. The air which we breath out contains less
oxygen (minimum about 15%) and more carbon dioxide (up to 5%). When you
breath in, not all of the air which passes your nose/mouth is delivered to
the lungs - there is a "dead volume" of air in the trachea which has never
reached the alveoli where gas exchange occurs. It is this dead volume which
is expired first, and contains more oxygen and less carbon dioxide than the
later parts of a single expiration.
Why this is important is said to be due to the different molecular weights
of the two gasses. Oxygen has a molecular weight of 32, while carbon
dioxide has a molecular weight of 44 (round numbers). Therefore, room air
(the start of an expiration) will be less dense than main-stream air (the
balance of the expiration), which will result in a higher vibration
frequency (pitch) for the same resonance structure (the instrument, lips,
reed, etc.) [Have you ever seen a demonstration of the effects of a breath
of helium on the pitch of the voice? Same phenomenon in the extreme.] The
difference in densities should be about 1.8% maximum.
Not mentioned in the source which I can't find is the effect of water vapor.
The difference in density between dry air and air saturated with water vapor
is about 2.2% at body temperature. However, water is added to the air not
only in the lungs, but from evaporation from all the passages, with the
result that the effective dead space volume is less for water vapor than for
oxygen/carbon dioxide. What effect there may be, however, is in the reverse
direction, since dry air is more dense than water-saturated air (water has a
molecular weight of 18).
So much for theory. In practice, I can't say I have ever noticed this
effect, although I have never done any careful studies looking for it. You
might try the following test - compare your normal observation with the note
produced if you exhale a bit before starting the note. I guess to be fair
you should exhale through the instrument, to make sure the air in the tube
(where it counts) is all exhaled air. I would be interested to learn if
there is any difference found under these conditions. (To do this properly,
you should not inform the person reading the tuner of what procedure you
used until after the data has been recorded.)
Hope this helps. Maybe its just a can of worms!
George W. Kidder III
Professor of Biology
Illinois State University
Normal, IL 61761-4120
(309)438-3085 gkidder@-----.edu
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