Klarinet Archive - Posting 000236.txt from 1994/02

From: Jordan Selburn <jselburn@-----.COM>
Subj: Re: Diaphragm vibrato
Date: Thu, 17 Feb 1994 18:08:26 -0500

Cary Karp writes:
>On Thu, 17 Feb 1994, Jay Heiser, wrote:
>
>> You'd have to put a scope on it to really analyze what happens
>> to the sound, but let me take a stab at what happens with flute
>> vibrato:
>>
>> The speed of the air blowing over the tonehole does effect
>> intonation. Creating pulses in the air flow then would cause
>> minor pulses in pitch. I'd never really thought about it before,
>> but I think that flute vibrato includes both pitch and volume change.
>
>Using an oscilloscope confirms exactly what theory predicts. Flutes are
>velocity controlled -- when you blow harder, pitch increases. Clarinets
>are pressure controlled -- when you blow harder, loudness increases.
>Diaphragm vibrato on a flute modulates velocity and therefore pitch.
>Diaphragm vibrato on a clarinet modulates pressure and therefore
>loudness.
>
>It is entirely possible that embouchure adjustments applied simultaneously
>with the diaphragm bouncing may cause secondary pitch changes on the
>clarinet and secondary loudness changes on the flute.

The distinction between the two types (lip and diaphram) seems to be that
of frequency modulation (FM, pitch changes from lip vibrato) vs. amplitude
modulation (AM, loudness changes from diaphram vibrato) of the primary
clarinet output frequency and harmonics. If you've ever looked at an AM
frequency spectrum, there are in fact "sidebands" or new frequencies near
the primary (or carrier) frequency. For example, the spectrum of an A440
with diaphram pulses/loudness changes (AM modulation) at 5Hz will have
outputs at 435Hz and 445Hz (plus others as well). While this differs from
an FM modulation of the same pitch, there are a lot of similarities - you
can't completely separate periodic loudness changes from periodic frequency
changes.

Caveat: it's been quite a while since I've done any communications theory
work and this is all off the top of my head. If anyone is interested in
more detail, I'll happily look it up.

Jordan
jselburn@-----.com