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. It allows the sound technician to adjust for optimal stereo and determine the makeup of errors such as an inverted signal. Many goniometers also provide a VU or PPM as a secondary function. A goniometer adapted for surround metering is called a 'jellyfish display'. This term was coined by DK-Technologies A/S from Denmark. Function 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. The channels are plotted on diagonal axes; a left-channel-only signal would form a diagonal line running top-left to bottom-right and a right-channel-only signal would form the opposite diagonal running top-right to bottom-left. A signal on both channels would provide components on both axes and thus expand the plot into two dimensions: a mono signal would produce a straight line angled according to balance; whereas a stereo signal, being asymmetrical, would produce a jittery and fluffy-looking ball (see image). An audio technician would typically begin a session by adjusting the equipment (usually with a