Harmonic Overtones and Resonance

An oscillation is said to go through phases, which are measured in degrees. A sine wave begins at 0° at an amplitude of 0 dB. The sine wave reaches its positive peak at 90°, returns to 0 dB at 180° and proceeds to its negative peak at –90°. From this point the sine wave returns to 0°. Resonance causes changes in the phase response at different frequencies, as well as amplitude changes.

Phase shift refers to sounds being delayed — or arriving early — by different amounts of time, according to frequency. 90° phase shift at 1 kHz is twice as many milliseconds as 90° phase shift at 2 kHz. When phase shift occurs, the number of degrees of shift varies with frequency. Phase shift is a property of resonance, and the degree of resonance is measured in Q, or its inverse, damping.