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From: phd@speech1.cs.cmu.edu.UUCP
Newsgroups: sci.electronics
Subject: Re: 3800 Hz notch filter [will] be used on CD masters
Message-ID: <1003@speech1.cs.cmu.edu>
Date: Thu, 9-Jul-87 04:42:02 EDT
Article-I.D.: speech1.1003
Posted: Thu Jul  9 04:42:02 1987
Date-Received: Sat, 11-Jul-87 17:53:05 EDT
References: <598@neoucom.UUCP> <67@sdeggo.UUCP> <1597@ihuxi.ATT.COM> <268@uvicctr.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 35
Summary: Adding Harmonics MIGHT improve the sound quality...

In article <268@uvicctr.UUCP>, collinge@uvicctr.UUCP (Doug Collinge) writes:
> I suggest that, since 3800 Hz energy in music will be mostly harmonics of
> lower frequency tones,  the thing to do is to put the music through a
> fuzzbox then filter out the 3800 Hz energy of the generated harmonics and
> intermodulation products.  This has the advantage of correlating the 
> synthetic stuff with the music that is already present - something the ear
> is extremely sensitive to.

This is a very interesting proposal! It is based upon the assumption that
most instruments generate harmonic partials in a fairly smooth fashion.
This is quite reasonable for certain instruments, for instance, the
brasses. However, some instruments have enharmonic partials (bells
come to mind), and some have very pronounced gaps (like the clarinet)
which give rise to the characteristic timbre. These might sound a little
strange when a hole that was there before suddenly gets filled when
running up a scale. Still, this is the sanest idea I've heard yet,
and might be well worth the effort. (Of course, this is only for the
real purists: I doubt most people will be able to notice the
difference without an A/B comparison anyway!)

I don't really know what a fuzzbox does (feel free to send me mail...),
but I assume it's some sort of time invariant, non-linearity. For
experimentation purposes, a saturating non-linearity might be reasonable
(i.e. a comparator), but I suspect that it is not optimal. Out of
curiosity, does anybody out there in netland know of any literature
on the the spectral properties of various non-linearities? (i.e. things
like exponentials, generic polynomials, and trigonometric functions...)

Paul H. Dietz, Graduate Slave Laborer in Trumpet Acoustics
phd@speech1.cs.cmu.edu	on ARPA
Dept. of Electrical and Computer Engineering
Caregie Mellon University

Disclaimer: I ASSUMED that the University was aware of my actions. However,
they patently deny that they were ever informed...