Phonograph playback added high percentage distortion that stayed inaudible under music

Evidence

This exercise is substantially a test of test records, which really is a test of the entire LP mastering, pressing and playback process. I participated in the creation of a test record, creating some of the sounds and signals recorded on the master tape. Comparisons of the master tape to the LP playback revealed that it was impossible to replay from an LP the same signal that was delivered to the (carefully chosen) mastering lab. When using pure tones or bands of noise, distortions were easily measured and easily audible. They registered in whole (sometimes high) percentages much of the time, and this applied to both harmonic and intermodulation versions. Yet, when the signal was music, the experience was mostly enjoyable. What is going on here? — Toole, Floyd E, Sound reproduction- the acoustics and…, 985