Practical Implications of Phasing

Phase, as mentioned in the section on acoustics, is a measure of the relative longitudinal position of two superpositioned sound waves. Phasing is a very important consideration for, amongst others, sound recording engineers.

Microphones and Phasing

Phase is invariably a factor affected by microphone placement. When two microphones collect sound from a source, any discrepancy in their distances from the source will affect phasing at certain frequencies. The phase shift will be most prominent in the higher frequencies, due to their shorter wavelengths. Some frequencies will exhibit some degree of cancellation, while others will be reinforced. This can also occur with a single microphone when the direct sound from a source interacts with early reflections from a nearby wall or other reflective surface.

Inline Signals and Phasing

With inline signals, phase shift occurs in tape recorders with misaligned heads. In this example, the playback head azimuth is out of alignment.

A properly recorded length of tape passing over this head will exhibit a phase shift and consequent azimuth loss. The track recorded on the top half of the tape, in the diagram, will be reproduced before the track recorded on the bottom half of the tape. Frequencies with cycles equal to one-half of this interval will be cancelled when combined. Additionally, attenuation will occur discreetly to each track output centered at a frequency dependent upon the width of the track and the degree of azimuth misalignment.

Another way that phase shift can be introduced to an inline signal is through the use of an electronic delay device, which effectively simulates reflection of sound.