Phase |
Phase describes where in its cycle a periodic waveform is at any given time. |
The relationship in time of two or more waveforms with the same or harmonically related periods gives us a measurement of their phase difference. | Phase cancellation occurs when two signals of the same frequency are out of phase with each other resulting in either a boost or cut in the overall level of the combined signal. |
Phase and Phase difference is a real-world issue in areas such as electrical wiring of audio equipment, signal path, and microphone placement during the recording process. Phase reversal can be a serious compromise of sound quality or a special effect affecting the perceived spaciousness of the sound depending on the context of its ocurrence. | For frequencies that are harmonically related a constant phase difference will result in a different waveform but this difference will not be detected by the ear. |
Consider the following example where two simple tones of different frequency are added together. In the first case we start with the two tones, a fundamental and first harmonic, in phase as diagrammed below: | The following diagram illustrates the resulting waveform after these two in-phase frequencies are added together: |
Now consider the following situation where the same two frequencies are added together with the second one out of phase by 90 degrees as illustrated below: | The following diagram shows the waveform resulting from the addition of these two: |
Although a different waveform has resulted due to the phase difference, this combination of frequencies will sound the same as the first, in-phase combination. |