One of the questions often asked by people just getting interested in high fidelity sound is: Numbers aside, just how does distortion sound?
Severe distortion of a musical waveform can be heard as a resping, harsh kind of tonality. Stringed instruments take on a "steel-like" quality. Wind instruments sound like kazoos. A soprano sounds as if she had a cold; a deep basso, as if he's gargling.
Distortions like these can be produced by a defective, or poorly designed, amplifier. They also can result when a loudspeaker is "overdriven" -- that is, fed with more power from the amplifier than it can handle.
When you hear such distortion from records, but not from other program sources (tapes or FM), chances are the phono cartridge or its stylus is defective. Another possible, but less often encountered, cause would be the phono-preamp circuit in the system amplifier. A simple glob of dirt riding on the tip of the stylus also can cause immense distortion when playing a record.
Another kind of distortion can occur even when a loudspeaker is properly powered by its amplifier, but -- due to inherent design limitations of the speaker -- it cannot negotiate the most demanding massed orchestral crescendoes of some music. What you hear then can be called an "accoustic traffic jam." The complex texture of the music becomes obscured; inner details of the musical score are blurred; softer sounding instruments are drowned out by louder ones instead of being allowed to contribute their subtle nuances to the musical whole. There is no definite name for this kind of distortion and no agreed-upon set of numbers to describe it. But with careful listening, you can detect it.
Uneven frequency response causes another kind of distortion. A departure from linear or "flat" response can be either upward (a "peak") or downward (a "dip").
A peak will emphasize a given part of the total response; a dip will slight some portion. When a dip extends over an appreciable part of the response and does not rise again to the average level (this occurs commonly at the extreme low and high ends of loudspeaker response), it is called a "roloff."
A pronounced bass peak lends a heavy or boomy quality to the sound. Midrange peaks cause the music to sound "honky" or "canned." High-frequency peaks make everything sound overly bright, strident, harsh.
A large dip in the bass, or an unusually severe rolloff, detracts from the music's natural tonal "foundation," and makes everything sound "thin." A depressed midrange causes the music to sound insubstantial, remote, without "body." A major dip in the highs, or a "premature rolloff" of the treble range fails to reproduce all the musical overtones that lend character and identity to different instruments and voices. It also degrades the transient response, the ability to furnish crisp and accurate response to short, intense signals such as drum-beats or plucked strings.
Some forms of distortion are mechanical in origin. Turntable rumble (motor noise) is one. Regardless of what the "numbers" say, if you hear a vague, low-pitched sound when your turntable is running, and the record itself has no bass tones at that point, you are hearing rumble. No turntable is entirely free of it, but in the better models rumble occurs at such a low level that it is virtually inaudible, even during quiet passages.
"Wow" and "flutter" (slow and rapid variations, respectively, in speed and thus in musical pitch) also can distort the sound. These annoyances will be most noticeable during long, sustained musical tones. They generally indicate a poorly made machine, or one that has a part going bad, such as a slipping belt or an out-of-round idler wheel.