In reproducing stereophonic sounds it is important to retain the "stereo" quality of the original microphone sound channels. The stereo separation and phase of each channel is important to know. In some cases, such as a recording studio, it is desirable to adjust these qualities to enhance the sound or the electronic performance of the processors.
Using the principle of the goniometer it is relatively easy to conjure up a measuring system that will display the separation and phase differences on a real time basis. The observation of the pattern of sound can then be adjusted or corrected as needed by the recording engineer.
APPLICATION
A Lissajous pattern can be traced out on the phosphorous screen of an oscilloscope in that its horizontal and vertical axis can be used for comparative representations of each of the stereo channels. Say, for example, the left audio channel is displayed on the vertical axis and the right channel on the horizontal axis.
These patterns will then show, graphically, the relative amplitude and frequency relation between the two channels. When music is shown, right channel on one axis and left channel on the other, it produces a scatter diagram around the 45 degree axis. If, for example the music program were monophonic and the content was identical in both channels the resulting Lissajous pattern would be a straight line at 45 degree tilt. When the two channels being viewed are true stereo music the pattern spreads and the dynamic scatter indicates the degree of stereophonic present in the program.
For a stereophonic representation of music the Lissajous pattern will be dynamically changing with the music or spoken word.
To the recording engineer - or the home amateur studio operator - these fast moving diagrams give a visual representation of the amount and amplitude of the left and right stereophonic energy. If, for example, one of the analog to digital converters in the PC studio shop was out of balance it would show the difference in amplitude during the balance check.
The test apparatus to set up this configuration is employment of an analog or digital oscilloscope. Many recording studios use a portable oscilloscope or PC scope to monitor the Lissajous patterns on a continual basis.
Goniometer - Oscilloscope Application APPLICATION
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