Phase problems in stereo field recording are most damaging in mono playback

Sound travels in waves with peaks and troughs. When two microphones are spaced apart, a sound reaching one mic slightly ahead of the other can create peaks in one channel and troughs in the other. When these signals are summed to mono, partial or total cancellation occurs at certain frequencies — called comb filtering. This rarely destroys a stereo mix entirely but can severely degrade mono compatibility. Mono playback is common on radio, small portable speakers, and streamed audio at low bandwidth. Phase problems are hard to detect on headphones; checking mono on a single loudspeaker is the reliable diagnostic. Signs include a ‘weak middle,’ exaggerated stereo, or thinned-out bass.

Examples

Check a stereo field recording by summing to mono in a DAW and listening for frequency dips or loss of center image. Compare ORTF and X-Y recordings of the same scene: the X-Y will typically degrade less in mono.

Assessment

Describe two symptoms of phase problems that appear only in mono but not in stereo. Explain why phase problems are harder to detect on headphones than on loudspeakers.