Meyer Sound SIM 3 User's Guide download pdf (Page 132)

126

CHAPTER 7

Using SIM 3

7.2.5. Average Time

The default Average Time (AvgTime) setting for Frequency Response measurements in SIM 3

is Constant Variance. With this method, the analyzer uses the same number of averages at all

frequencies to display the traces.

The other setting is Constant Time, which places the trace on the screen based on the last

16 updates, in a ﬁrst in / ﬁrst out manner. Because a greater number of averages are done

in the higher frequencies than in the lower frequencies over a given period of time, choosing

this setting might under certain conditions make the higher frequency portion of a frequency

response trace appear more solid with less ﬂuctuation and moving around.

TIP: It is usually best to leave this setting in the default position — Constant

Variance.

7.2.6. Time Weighting

SIM 3 uses exponential time averaging for Time Weighting, which is a running time

average where older samples are given exponentially decreasing weight as compared

with more recent samples. The Time Weighting dropdown in the Band and Line Spectrum

measurements has three settings, and they do have some effect on how the data is acquired

and drawn in the trace graphs.

■ Slow — the default exponential time averaging, which uses a time constant of one

second.

■ Fast — which uses a time constant of 125 milliseconds.

■ Accumulate — the data is continually collected and averaged until the measurement

is restarted or changed.

Figure 7.7. Selecting Time Weighting from the dropdown list

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Meyer Sound SIM 3 User's Guide Page 132