When commissioning or troubleshooting a digital audio system, remember to check the eye pattern. The eye pattern is a representation of the analog voltage that carries the digital audio information and is displayed on an oscilloscope.
Some scope-based or raster-based specialized audio measurement equipment include the eye display along with calibrated graticules to help determine such values as signal amplitude, jitter, rise time and overshoot.
The eye display checks the integrity of the transmission path as well as the digital audio signal output from each piece of equipment at each stage along the signal path.
If all is well, the eye display looks less like an eye than a box with a flat top and bottom, and sides that show distinct crossings (X-shapes). But, if there are problems, the eye starts to close in and the sides start to round off. The lines that represent the eye start to become thicker.
The more the eye closes, the less likely an AES receiver will be able to properly detect the transitions that indicate a one or a zero. If things get really bad, and the eye is closed (or nearly so), a receiver may not be able to detect the AES signal at all.
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