Re: Interesting case related to pitch perception

[Hiroko Terasawa <shiraiwa@xxxxxxxxxxxx>]

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

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

http://www.wfg.woodwind.org/oboe/ob_bas_1.html
http://www.wfg.woodwind.org/oboe/ob_bas_2.html

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
> Hz.
>
> Arturo
>
> --
> __________________________________________________
>
> 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
http://ccrma.stanford.edu/~hiroko/