Goniometer (audio)

A goniometer is often included in analog audio equipment to display a Lissajous figure which shows the amount of stereo (that is, phase differences) in a dual-channel signal.

[1] It allows the sound technician to adjust for optimal stereo and determine the makeup of errors such as an inverted signal.

Its function is to plot a signal on a two-dimensional area so that the correlation between the two axes (audio channels, or phases) becomes apparent.

An audio technician would typically begin a session by adjusting the equipment (usually with a 1 kHz mono tone) so that the output produces a vertical plot line.

From the display, one can get a good feel for the audio levels for each channel and the amount of stereo and its compatibility as a mono signal.