Guralp Systems CMG-CD24 - Manual (Page 31)

Operator's Guide
The Ratio column determines by what factor the STA and LTA must
differ for the trigger to be passed. Finding the ratio most suited to your
needs is best done by experiment. Too high a value will result in
events being missed, while too low a value will result in spurious non-
seismic noise triggering the system. Like the averages, their ratio is
continuously recalculated for all components. Note that none of the
boxes are allowed to be empty, and so you will need to enter the new
value before removing the old one. Alternatively, you can use the up
and down cursor keys to change the values.
For example, setting the STA to 1 second, the LTA to 10 seconds and
the Ratio to 4 would give rise to the following trigger behaviour:
Usually, the values of the STA period, the LTA period and the Ratio
will be the same for all checked channels. For convenience, Scream!
will automatically fill in other values to match ones you enter. If you
want to use different values for some channels, you should clear the
Common values check box before altering them.
Once you have enabled the STA/LTA triggering method on a particular
channel, you can use the Control window to change the values of the
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