User guide

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CHAPTER 7
Using SIM 3
7.5. UNDERSTANDING COHERENCE (VALIDITY OF THE MEASUREMENT)
7.5.1. Coherence Overview
The coherence threshold is the level at which the SIM 3 analyzer accepts that the correlation
of the data at the two measurement points is sufficient to present that data as a trace
within the viewer at a particular frequency or subset of frequencies. Coherence is shown
as a percentage, and the higher this percentage is, the more likely the measurement at that
frequency is accurate.
7.5.2. Coherence in Frequency Response Measurements
Within every SIM 3 measurement, it is normal to see numerous peaks and dips within the
red Coherence trace, especially when using live program material as a measurement source
and when measuring at a greater distance from the loudspeakers. The dips indicate lower
coherence.
NOTE: The corresponding frequency response trace (amplitude over
frequency) is more likely to be missing or showing a sharp and usually narrow
dip in the areas where low coherence is indicated.
Figure 7.22. Frequency Response trace with Coherence trace