However, these measurements do not provide much useful information about the sonic qualities of the amplifier. It is much more important to improve the current response of the amplifier. Suppose we took an amplifier and substituted batteries for the power supply. The sound would definitely improve because batteries have faster current response and no ripples. However, while the amplifier will sound better, the THD and TIM measurement will not change.
Stressing components can also impact their sound.
A transistor's saturation voltage will change as the transistor becomes warmer. An amplifier will sound different whether it is cold or it is hot. Stressing a semiconductor for long periods of time can cause a change in the sonic quality of the amplifier. The very best designers in the world must take all these factors and other factors into consideration. Where cost is no object, fewer compromises are required.