Omitted factors in audio circuit design

Traditional measurements of audio amplifiers use test signals that do not represent conditions of actual use. TIM measurement is one factor in improving the correlation between audible and measurable differences in circuitry. Additionally, many circuits incorporate non-linear elements that appear to be distortionless at conventional measurement frequencies, but can be significant sources of distortion when subsonic or supersonic frequencies are included. This paper describes some of these non-linear elements and their effects on actual circuit performance.