etan@tellab1.UUCP (Nate Stelton) (05/23/84)
I can't really say that I disagree with Mr. Hughs' article, but I feel compelled to approach the explanation of distortion somewhat differently in some of his categories. Pitch distortion There are three possibilities of this that I can think of: 1 Wow. The slow variation of playback speed (of a record or tape). 2 Flutter. Fast variation of playback speed. 3 Wrong playback speed. They can be most easily found in the following types of recordings: Wow - very slow organ music Flutter - solo acoustic piano or acoustic guitar music Wrong speed - vocal material Harmonic distortion This is the presence of higher order harmonics. HD is difficult to detect since most musical instruments have varying degrees of this. The sound could be described as richer. While listening, pick one instrument and listen to see if you hear the note an octave above also. The best way to detect HD is with instrumentation (obviously). It may not sound bad, but it's preventing you from hearing the real thing. When you hear an electric guitar note sustaining and it fades into the note 1 octave above (Hendrix, Van Halen) that's extreme HD within the guitar amp (which, of course is purely intentional). Overload Distortion Also known as 'clipping', this is what you get when you drive an amplifier stage beyond what it is spec'ed at. A good example would be the aforementioned "ghetto-blaster effect". I think this the fuzzy sound that Mr. Hughes was referring to. Intermodulation Distortion When low frequencies interact with high frequencies in such a way as to affect them, this would exemplify IM. Tape medium and speakers are the formost culprits of this. A good example would be if you hear a cymbal crash decaying and a loud bass note occurs and causes the cymbal sound to 'break up'.