Changing a tone’s phase alters both its temporal envelope and its instantaneous frequency.

Evidence

To illustrate the effect of such a phase change, Fig. 7.13 shows the envelope (left side) of the resulting time function, p(t), and the instantaneous frequency, f(t), (right side) of a complex composed of three tones of equal amplitude and equal frequency distance, .:1f. For () = 0, the top panel shows the envelope to be an overmodulated amplitude modulation. The corresponding instantaneous frequency shows periods of constant frequency and Dirac impulses of opposite signs at the zero-crossings of the envelope. For () = 30°, the envelope shows no zero-crossing and the instantaneous frequency consists of deviations that are relatively large. For () = 60° and 90° the envelope of the sound pressure function becomes more symmetrical, and shows two equal variations within one period. The corresponding changes in instantaneous frequency again show deviations in both the positive and negative direction that reach only half the value of the peak obtained for () = 30°. Figure 7.13 indicates that two effects are associated with phase changes, i.e. variations in the envelope of the sound pressure’s temporal pattern and variations of the instantaneous frequency. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1084

Categorization

• DEFINE: Illustrates how a phase parameter shift produces two concurrent acoustic effects - envelope variation and instantaneous frequency variation - clarifying the physical basis for phase perception experiments.