Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 (Tek) 9/26/83; site tekchips.UUCP Path: utzoo!watmath!clyde!burl!ulysses!harpo!decvax!ittvax!dcdwest!sdcsvax!sdcrdcf!hplabs!tektronix!tekchips!wm From: wm@tekchips.UUCP Newsgroups: net.audio Subject: Re: What does "distortion" sound like? - (nf) Message-ID: <809@tekchips.UUCP> Date: Sun, 20-May-84 16:13:15 EDT Article-I.D.: tekchips.809 Posted: Sun May 20 16:13:15 1984 Date-Received: Sat, 26-May-84 12:29:58 EDT References: <32900004@convex.UUCP> Organization: Tektronix, Beaverton OR Lines: 169 A simple definition of audio distortion is anything that happens to the music that you didn't want to happen. If this sounds stupid, let me give a few examples, and then I will try and answer what I really think you were asking. Example: When you turn the volume control on your stereo up, you probably want the music to get louder. If instead, turning up the volume control overdrives the amplifier so that it clips, or overdrives the speakers so that their voice coils try to "reach out and touch someone", then that's distortion. If you purposely turned up the volume control so that the amplifier would clip (ignoring what that will do to the rest of the system, or to your ears), because you like to listen to your favorite Spinal Tap album that way, then that is NOT distortion (to you). 'nother example: If the heads on your tape deck get dirty, so that you can't hear the high frequencies as well, then that is distortion. If you turn down the treble control on your stereo so you can't hear the high frequencies as well, that is not distortion (to you). To a "golden ears" listening to classical music, then, a useful definition of distortion is anything that makes the music sound different from "the real thing" (whatever that really is). What I really think you are asking: commonly heard distortions in a stereo system, and what you can do about them. Clipping. When an audio signal is larger than the circuit trying to handle it was designed for. Called clipping because the tops and/or bottoms of the waveform get clipped off, like with a machete. Sounds just like that, like someone took a machete to the music. Note that it is VERY common to plug electric guitars into what is called a "Fuzz Box" which does exactly that, it clips the sound. When done on purpose it is not distortion, as noted above. When not done on purpose, it can destroy amplifiers, speakers, ears. To hear what it sounds like, turn the volume control on your stereo up until your cat leaves the room. If you have no cat, fake it. Clipping mostly causes Harmonic Distortion. To fix, get a more powerful amplifier and speakers that can handle the extra power. And new neighbors. Or use headphones, and go deaf alone. Actually, most any normal amplifier is clipping quite often. To reproduce the peaks of the waveform from a piano, at normal room volume, with reasonable speakers, would take at least 5000 watts. Make that 15,000 just to give you a couple of dB headroom. Not very many people without football stadiums have amps like that. So the point is not to eliminate clipping, but both to minimize it, and to clip "softly", i.e., round the corners off smoothly, instead of cutting them off sharply. Sharp corners have lots of high frequencies, and get on your nerves. Another interesting effect. Music sounds "too loud" because of clipping, more than because of the actual sound level. Try this experiment: Play a piano. Observe mother come in and praise you for such pretty music. Play similar piano music on standard (less than 15000 watts) stereo at same volume. Observe mother come in and tell you to turn the stereo down before you go deaf. Fuzz boxes are one reason that rock music sounds "loud and obnoxious" even when played at low levels. Harmonic distortion sounds like one frequency turning into a higher, related frequency. Play middle C on your piano, then play the C above middle C. The higher note is the second harmonic of the lower C. If a concert pianist plays middle C, and it come out of your stereo like 15 different notes, most of which are higher in frequency than the real note, that is harmonic distortion. Intermodulation Distortion. Caused by anything that changes the shape of a waveform in a way that is not desired, other than clipping. Tone controls cause intermodulation, but as noted above it is not distortion if you want it. Purists get stereos that can switch the tone controls out of the circuit. All the same applies to graphic equilizers. Intermodulation is caused by two different frequencies going through a non-linear circuit and modulating each other. If you have two notes, of frequencies A and B, and pass them through a non-linear circuit, then you get A, you get B, but you also get A+B, A-B, B-A. If you also have some harmonic distortion, you also get things like 2*A-B, and any other conceivable combination. Intermodulation distortion doesn't sound as bad as harmonic distortion (especially clipping), but it can make things sound muddy, or indistinct, with all those other frequencies jumping around that have nothing to do with the original music. Hum and Noise. Hum and noise collectively make up the "noise" part of signal to noise specs. The power line is 60Hz, which most everyone can hear. Even when not directly audible, this can cause problems, because the hum signal can intermodulate with the music and make everything mushy. Noise typically comes from high gain, low level stages, like the phono or tape preamp. To hear what noise sounds like, turn your FM tuner between stations, with muting off. To actually hear the noise (and hum) in your system, without playing a record switch your stereo to phono, and crank the volume up. The stuff that sounds like the ocean, and isn't hum, is noise. It is caused by electrons bouncing around when they get excited and not doing what your stereo tells them to do because you didn't pay enough money for it and electrons don't take orders from cheap stereos. Dirt. Dirt on your tape heads. Dust on your phono needle. To see what it sounds like, clean it off and compare to what it sounded like before. Mistracking. When the needle on your phono is literally trying to jump out of the record grooves. Most often caused by warped records, but even unwarped records can mistrack due to the wrong stylus pressure (typically too little). A stylus with too little pressure that is mistracking can cause more damage to records than using more pressure. To see what it sounds like, take a record you don't want any more, and decrease the stylus pressure until it mistracks. Sounds somewhat similar to clipping, but different enough so that you should be able to recognize it. TIM. Sort of like the electronics of your stereo mistracking because they can't move as fast as the sound. Mainly caused by using op amps with too much negative feedback. Can only be heard by golden ears using test records. Other stuff. Distortion caused by not using gold plated everything, and by sparing any expense for your stereo. Very difficult to get rid of this kind of distortion, because they will always find something else for you to spend your money on. And just when you think you have gotten rid of all that nasty distortion, you start to get a new kind of distortion, that caused by creditors ringing your doorbell while you are trying to listen to music. Digital. I won't try and go into this in detail. There is distortion caused by quantization errors (the fact that volume has to change in discrete steps). There is aliasing, and sampling errors. Most of these types of distortion are fairly subtle. Don't worry about them until your stereo costs more than $3000. WHAT DISTORTION SOUNDS LIKE. What is more important is what it doesn't sound like. Stereos are of good enough quality, even for fairly cheap systems, that you will probably not directly hear distortion most of the time. But distortion makes listening to your stereo less enjoyable. Do you find your friends asking you to turn the music up or down? Do you suddenly get the urge to switch stations, when you are listening to a tape? Do you usually come home from work and feel like listening to music? Stereo systems are to enjoy. If you are not enjoying yours, it might just be because of distortion. Wm Leler 503/627-5151 wm.Tektronix@csnet-relay {ucbvax|allegra|decvax|ihnp4}!tektronix!wm