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From: sethb@Morgan.COM (Seth Breidbart)
Newsgroups: rec.audio.high-end
Subject: Re: Deliberately designed to measure great AND sound rotten
Message-ID: <8585@uwm.edu>
Date: 28 Dec 90 14:26:41 GMT
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu


In article <8551@uwm.edu> noamb@over.cs.caltech.edu (Noam Bernstein) writes:
>One such box I've heard measured perfectly in every measurement anyone (at
>some audio engineering society meeting) could come up with, except listening 
>to music.  With actual music, the sound sucked.  It was a digital circuit 
>which looked for symmetrical waveforms.  When the input was symmetrical, 
>it shorted the input to the output.  When it wasn't symmetrical, it didn't 
>conduct.


That's an interesting idea.  How did it handle the following test:

Play music through it.  Subtract the output from the input.  Take the ratio
of the power of the result to the power of the input (that is, the ratio of
the integral of the square of the voltages).

In some sense, that's a measure of distortion.  0 is shorting the input to
the output, 1 is an open circuit (output = 0).  You might want to "normalize"
the output by multiplying by a constant before subtracting, using the
constant that minimizes the resulting measure.  This lets a perfect amplifier
score 0.

It should also be fairly easy to design a box that has wonderful specs when
played into a resistor, but which has terrible specs (and sounds terrible)
when played into a "real" speaker.

Seth			sethb@fid.morgan.com