When we hear the word distortion, we think guitar amps and that crunch sound from turning the volume up too loud. That’s just one type of distortion, called clip distortion. There are several types of distortion, each with its own unique sonic signature. Distortion is not always that crunchy noise, sometimes it will add warmth, character, phase errors, an change in frequency response, or just white noise.
Really, distortion is any deviation from the original sound. It can be defined as any change from the original sound wave, or any information lost or added compared to the original sound. Any time the audio goes through any electronic circuit, tiny amounts of distortion are always introduced, often just as slight imperfections.
Think about a camera taking a picture. A camera lens, no matter how high quality the lens is, can only introduce imperfections to the image. No matter how good the lens is, it will never improve the image, or add greater resolution, or improve the accuracy of the picture. It can only subtract, skew or distort the image. Sometimes specialty lenses are desired, such as tinted or tilt shifted, but this is really just another form of distorting the original image.
So, it’s the same with audio. Any audio circuit can never add to the original fidelity, it can only subtract from it and distort it in one way or another. Sometimes this distortion is desirable in the warmth or sonic character that is added, and sometimes the distortion is undesirable, such as lower fidelity, muddy sounding, or simply adding white noise. Usually, it’s a combination of all of the above.
Clip distortion is probably the most prevelant type of distortion. This is caused when the wave form runs out of headroom, and the top is flattened off. This causes what’s called harmonic distortion. For more information about harmonics, check out lesson 1.3.1, how Sound is made up of different frequencies, and also check out the video in the tips and tricks and theoughts from behind the desk section about tube vs solid state.
I’ll touch on it a little here though. There are certain types of distortion that are musical and pleasant sounding. These are odd and even order harmonics. Let’s say the fundamental note is 100hz. The second harmonic is 200 hz, the 3rd harmonic is 300 hz, the fourth harmonic is 400 hz... etc. Harmonic distortion is the addition of frequencies that are related to the original frequency. These can be very musical sounding, because second, fourth and eights order harmonics are octaves of the original note, and third harmonic produces an interval of a perfect fifth. They resonate pleasantly to our ears because they are directly related to the original tones. When you add frequencies that are not related, they tend to be dissonant, and discord sounding.