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MMD > Archives > December 2003 > 2003.12.12 > 04Prev  Next

Apparent Frequency Change With Intensity
By John A. Tuttle

Hi All,  Maybe someone can explain this to me.  Today, while on hold
on the phone, there was a beep-beep sound that played about every ten
seconds.  Initially, I had the phone right up to my ear and the beep
sounded like an "A".  Then, when I tilted the phone at an angle to my
ear, the pitch of the beep seemed to be higher, like an 'A#'.

At first, I thought I just wasn't paying close attention.  So, I tried
it a few more times (yes, I was on hold for a few minutes).  Sure
enough, every time the phone was next to my ear, the pitch 'sounded'
lower than when the phone was at an angle.  Naturally, I understand the
Doppler effect, and how it effects the pitch of a tone, but the phone
wasn't moving -- it was stationary.

My thought is that the difference might have something to do with the
fact that when the phone was flat against my ear, the sound was going
'straight in'.  Whereas when the phone was tilted, the sound had to
bounce off my outer ear to get into my inner ear...

Does that make sense?  And if it does, can we ever say for sure that
the pitch we hear is actually the pitch that is being generated?  And
with the exception of the phone or a headset, how can we tell if the
angular difference between the 'source' and our ear is effecting the
pitch we actually 'hear'?

Makes me wonder if it wouldn't be better to use an amplifier and a
headset when tuning a piano.  At least that way I would be certain that
the sounds are all coming 'in' from the same direction.  Hmmm...


John A. Tuttle
Brick, NJ, USA

 [ The perception phenomenon might be related to a familiar
 [ characteristic of the harmonica (and the clock pendulum, too):
 [ the frequency becomes lower as the amplitude of the vibration
 [ increases.  -- Robbie

(Message sent Fri 12 Dec 2003, 18:58:04 GMT, from time zone GMT-0500.)

Key Words in Subject:  Apparent, Change, Frequency, Intensity

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