User guide

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CHAPTER 7
Using SIM 3
(often the microphone in the room) is poorly related to the source signal. Low coherence in
a Processor measurement would typically indicate that a delay within the signal processing
path has not yet been compensated for in SIM 3 using Autoset Delay.
CAUTION: The data from the two measurement points used for the transfer
function must be synchronized in time in order for the response to be valid
(and for the Coherence trace to show coherence). Use the Delay Finder measurement
and either Autoset Delay or a manually entered delay time in order to exactly
synchronize the first (“source”) signal to the second signal. Very low and/or “stair-
stepped” coherence traces in the higher frequencies are a visual indication that the
data is not synchronized.
TIP: Low coherence in the Room or Results trace can indicate a variety of
problems with reflections, multiple loudspeakers covering the same location
with different path lengths, incorrect delay settings to the loudspeakers, physical
misalignments, or the internal delay in SIM 3 for that section of the branch not being
properly set.
Figure 7.24. High-frequency shelving in Coherence trace shows measurement time offset
7.5.7 Viewing Coherence as S/N Ratio
The coherence of the measured Frequency Response trace can also be shown as S/N (signal
to noise ratio). This S/N trace is shown in red along with the response trace, and also can
be shown full-screen, half-screen, and 1/3 screen. A S/N trace that is above the 0 point is
related to higher coherence, and one that is below the 0 point with less coherence.