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Re: Interesting case related to pitch perception

Hello Arturo,
I'm not a specialist - but I try to explain a bit.

first, the fingering for the oboe c5 and c6 are:


According to that, c5 and c6 are essentially same fingering, with c6 have tiny opening to create some leakage of air. The basic fingering of c5 gives the air column vibration inside oboe to have a wavelength, say L. the harmonic series of 500 Hz includes harmonic series of 1500 Hz as well. Creating the air leakage at the octave key emphasizes the harmonic series of 1500Hz (L/3 wavelength) but does not remove the harmonic series of 500 Hz. what you see is the 500Hz harmonic series with exaggerated 1500Hz harmonics contents by the use of octave hole.

That's the reason why you observe multiple harmonic series, from the view of the resonator (air column of the wind instruments.) I don't know much about the function of double-reed - it usually interacts with air column resonance and has something to pronounce the 1500Hz contents better.

You can find such information from musical acoustics textbooks. my favorite is the physics of musical instruments by Fletcher and Rossing.

 - hiroko

On Jul 27, 2007, at 11:13 PM, Arturo Camacho wrote:

Dear members of the list,

I am analyzing the spectrum of musical instruments in a pitch-related
study and found something that puzzles me: the spectrum of an oboe playing
the note G6 (approximately 1500 Hz pitch) contains peaks not only at
multiples of 1500 Hz but also at each multiple of 500 Hz. This was
observed in a sample taken from the University of Iowa Musical Instruments
Database (http://theremin.music.uiowa.edu/MIS.html), specifically, the 8th
note in the file "oboe.pp.C6Ab6.aiff". I do not know much about wind
instruments, but my guess is that the position used to play G6 is probably
the same used to play C5 and the only difference is the pressure in the
mouth. This could leave the harmonics of C5 alive and that is why there is
energy at multiples of 500 Hz. If someone know the reasons of this effect
please let me see the light, because it would be nice to offer an
explanation of this in my study.

As an aside, this is an interesting example of a case in which the pitch
is different from the fundamental. From the log-magnitude of the spectrum
it is very clear that the signal consists of multiples of 500 Hz (although
with boosted 3rd, 6th, 9th, etc. harmonics), and therefore, the
fundamental frequency, if any, should be considered as 500 Hz and not 1500



Arturo Camacho
PhD Candidate
Computer and Information Science and Engineering
University of Florida

E-mail: acamacho@xxxxxxxxxxxx
Web page: www.cise.ufl.edu/~acamacho


Hiroko Terasawa