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From: csc@watmath.UUCP (Computer Sci Club)
Newsgroups: net.audio
Subject: Re: What does "distortion" sound like?
Message-ID: <7819@watmath.UUCP>
Date: Tue, 22-May-84 11:36:36 EDT
Article-I.D.: watmath.7819
Posted: Tue May 22 11:36:36 1984
Date-Received: Wed, 23-May-84 19:01:05 EDT
References: <32900004@convex.UUCP>
Organization: U of Waterloo, Ontario
Lines: 69

This question actually merits more than the superficial treatment it
has been getting so far.  Description of sounds is rather difficult
as the terms, "muddy", "crisp", "metalic" etc. often seen on this net
are somewhat ambiguous and can be quite useless to the neophyte.
The best way to describe sounds is to give examples.

Noise: The most straightforward type of distortion, noise is additions
       to the signal you are amplfying that are not related to the signal.
       Noise can be heard quite easily, listen to a system with no input
       and turn up the volume, or "white noise is the noise you hear when
       you turn on the TV and there isn't any station". To hear noise 
       together with music play a tape and turn of the Dolby, (if the
       deck doesn't have Dolby play a tape :-) ).  Clicks and pops due
       to scratches on records are another common type of noise.
       
       Noise is generaly fairly easy to identify, you hear it as
       something seperate from the music, "tape hiss" for instance.
      

Frequency Distortion.   This occurs when some frequencies are amplified
       more than others.  To hear it fool around with the tone controls
       on your amplifier.  If you have access to an equalizer fool around
       with that to hear more subtle frequency distortion.

       Frequency distortion is much harder to pin down.  You cannot
       seperate it from the music.  If you turn the bass way down or
       the treble way up it is fairly clear what is happening, but
       if you just tweak the controls a bit the music will sound
       different but it is not clear why.  It has been shown that
       humans can hear quite small amounts of frequency distortion, but
       that they do not always identify it as such.  Frequency distortion
       has been cited as the reason some people perceive a difference
       between CD's and Lp's

       Pitch change (mathemaically I think this is harmonic distortion but
       who cares :-) )  If the pitch of the music is shifted uniformly up
       or down, we have another type of distortion.  A good example of
       this in the extreme form is a 33 1/3 record played at 45.  Small
       amounts of pitch change are not annoying (or even likely to be
       detected unless you have perfect pitch) if they are constant.
       If the pitch change varies with time (e.g. the record speeds up
       and slows down) this can be very annoying.  The best way to
       detect this is to play some long steady note and listen for
       variation (test records and tapes have such notes for this reason).

Harmonic distortion,  This is distortion that introduces frequency components
       not in the original signal.  An extreme example is the distortion
       of an electric guitar used for effect by many groups.

       In its extreme form harmonic distortion is quite easy to detect.
       (The usual description is that the music sounds "fuzzy")  In milder
       forms it is much more difficult to hear.  There is a large body
       of opinion that maintains that the amount of harmonic distortion
       produced by any reasonably good amplifier is quite inaudible.  There
       are no unanimous opinions in the audio field.

Small amounts of distortion are very difficult to hear.  In the end you can
only compare to some standard, "actual" sound, very difficult to do if you
have poor audio memory.  I am of the heretical if it sounds good to you
go for it school of audiophiles, who listen quite happily to our $800.00
systems with our tin ears.  How low a level of distortion is acceptable
and whether some types of distortion actually sound better, can be
determined by listening to a wide variety of music on a wide variety of
systems.
                                           William Hughes

P.S.  Anyone have any other tricks for detecting small amounts of distortion
      (like listening to steady tones to detect variation in pitch)