There is no direct and unambiguous correlation between low THD/IMD figures and the subjective quality of sound as perceived by the human ear.

• The researcher must be able to analyze not only the harmonic frequencies of the fundamental tone but all oscillations within a defined frequency range around the test signal.

• The test signal should not be an ideal periodic sine wave, but rather a complex, non-stationary pulse signal, which more closely resembles real-world audio signals.

• The researcher must have the ability to create a specific mix of several non-multiple frequencies to quantitatively study multiple intermodulation.