Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!malcolm
From: malcolm@Apple.COM (Malcolm Slaney)
Newsgroups: comp.dsp
Subject: Re: Autocorrelation Pitch Tracker
Message-ID: <51534@apple.Apple.COM>
Date: 15 Apr 91 15:59:42 GMT
References: <1991Apr6.062906.11886@cs.cmu.edu> <51258@apple.Apple.COM> <1991Apr13.013025.26614@agate.berkeley.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 57

doug@eris.berkeley.edu (Doug Merritt) writes:
>This is an interesting subject. I have to wonder whether your experiment
>might be faulty, though. What if you're simply uncovering funny behavior
>in your sound system rather than in your ear, for instance? 

Well, nobody has ever accused the native Macintosh sound system of being
high fidelity but the effect is true.  I quote from the booklet that 
accompanies the Auditory Demonstrations CD (as done by the ASA):

	How long must a tone be heard in order to have an identifiable pitch? 
	Early experiments by Savart (1830) indicated that a sense of pitch 
	develops after only two cycles. Very brief tones are described as 
	"clicks," but as the tones lengthen, the clicks take on a sense of 
	pitch which increases upon further lengthening. 

	It has been suggested that the dependence of pitch salience on 
	duration follows a sort of "acoustic uncertainty principles," 

				    delta F   Delta t = K, 

	where Delta f is the uncertainty in frequency and Delta t is the 
	duration of a tone burst.  K, which can be as short as 0.1 (Majernik u
	and Kaluzny, 1979), appears to depend upon intensity and amplitude 
	envelope (Ronken, 1971). The actual pitch appears to have little or 
	no dependence upon duration (Doughty and Garner, 1948; Rossing
	and Houtsma, 1986). 

	In this demonstration, we present tones of 300, 1000, and 3000 Hz in 
	bursts of 1, 2, 4, 8, 16, 32, 64, and 128 periods. How many periods 
	are necessary to establish a sense of pitch? 

	Commentary

	"In this demonstration, three tones of increasing durations are 
	presented.  Notice the change from a click to a tone. Sequences are 
	presented twice." 

>Besides all that, consider the Fourier domain of this. 
Bad move.  First the signals I am talking about were synthesized in the
time domain...Mr. Fourier wasn't involved.

Second, there is a famous hearing researcher (von Bekesy?) who once said
something like
	Dead cats and Fourier transforms have harmed hearing science more
	than anything else.
Dead cats are a no-no because it is now known that most of what makes the
ear work are the non-linearities and active gain control mechanisms in the
ear.  Taking measurements from an cochlea that is not living gives you a lot
of meaningless data.

Fourier transforms are not good because the ear is non-linear.  Fourier 
theory is great for linear systems but the ear is far from linear.  Sure,
we all talk about frequency and such but one must remember that it doesn't
always make sense in the ear.  A lot of people argue about how the ear works
but nobody thinks it computes a Fourier transform.

								Malcolm