Test signals for music reproduction systems

Experiments with both long, continuous tones and short, transient tones have shown that the human ear is insensitive to relative phase differences between fundamentals and overtones. Short notes from a piano and from a drum are studied here to show that the phase requirement for music reproduction is that the group velocity of the system be constant in the relatively narrow regions surrounding the fundamentals and overtones. The phase velocity across the audio spectrum does not have to be constant, thus easing the requirements on loudspeakers, crossover networks, and tape recorders. Pulse-testing schemes require minimum-phase behavior of a system for simple interpretation and therefore tend to overtest a music reproduction system. Random noise can be used as a test signal if elaborate processing equipment is available. However, the sinusoid is still the best test signal for determining distortion and relating device performance to theory.