goniometer
In general, a goniometer is a protractor. However, the term is also used in acoustic metrology for a device for measuringstereophony, which is why it is also called a stereometer.
A goniometer shows on a display the stereo reproduction and the distribution of the stereo sound in the room. The display uses an angular coordinate system with a center axis and two axes offset 45° from the center axis for the left and right channels. When plotting a mono signal applied to both channels, the goniometer plots a straight line on the center axis. If the mono signal is applied to one of the two channels, a straight line will be formed at an angle of 45°. Depending on whether the signal is applied to the left or right channel.
Stereo plots spread out between the two outer axes and allow conclusions to be drawn about the stereo width and the weighting between the two channels. In addition, phase problems between the two channels can be detected with goniometers and analyzed using Lissajous figures. Phase shifts become apparent when the same frequency signal is applied to both channels and the displayed Lissajous figure forms a circle or an ellipse.