STA/LTA Triggering Information

STA/LTA stands for Short Term Averaging / Long Term Averaging. More information about LTA/STA triggering can be found here: Tuning of Seismic Networks This is an excellent description on how STA/LTA works and what numbers should be used for the different channel menu  items used for triggering event files. Note: This link is not working. I have contacted the Webmaster to see if they can fix it. In the mean time here are several links I found regarding STA/LTA:


To enable this mode of triggering go to one of the channel setting menus (ALT-1 to ALT-8 keys) and set the Threshold Point (this menu item was titled "Alarm Point" in older version of SDR) number to 0 (zero).  

The following menu items are used for STA/LTA triggering:

STA/LTA Threshold: When the STA/LTA ratio goes above this number the channel will go into a pre-trigger or trigger mode depending on the Threshold Number. Input is a floating point number usually in the range of 3.0 to 50.0.

STA/LTA Times: Two floating point numbers are entered in this field. The first number is the STA window time in seconds and the second is the LTA window time in seconds. If you only enter one number the STA time will be updated. To change the LTA time both numbers must be entered. Normal ranges of numbers for STA are .2 to 3 seconds and LTA 10 to 60 seconds. The actual window time depends on the system sample rate. At 100 samples per second the resolution is 10 milliseconds, at 50 sps the resolution is 20 ms etc.

LTA Minimum: This menu items set the minimum the LTA can go down to. This sets the overall trigger sensitivity of the channel. The higher the number the less sensitive the channel will be to noise or a real event. The default os 0 or no LTA minimum limit.

Trigger Time: Sets the time in seconds the channel will stay in a pre-trigger condition. Default is 10 seconds.

Threshold Number:  For a channel to go into an alarm or trigger state the STA/LTA threshold must happen Threshold Number of times within the Trigger Time above. This menu item was titled "Alarm Point Number" in older version of SDR. This number is also used if the Threshold Point field is non zero. With STA/LAT enabled normal numbers for this field are 1 to 4. If set to 1 the channel will trigger whenever the threshold is reached. Normal ranges with STA/LTA triggering turn off are 20 to 100.

STA/LTA Status Display: 

To monitor the STA/LTA process go to the single channel display screen by pressing the 1 - 8  key.  Pressing the ALT-S key will toggle between the normal data high / low display to the STA/LTA status display. The status numbers are:

STA/LTA: CurrentSTA CurrentLTA  STA/LTA-RATIO  MaxRatio  PreTriggerCount TriggerCount

The PreTrigger count is the number of times the channel went above the STA/LTA Threshold. The TriggerCount is the number of times the channel triggered. If Threshold Number = 1 both numbers should be the same.  Press the 'C' key to clear out the MaxRatio, PreTriggerCount and TriggerCount numbers. 

The new release (versions 2.75 or higher) of WinQuake can display the STA/LTA ratios within an event file. This feature can be used to help you select the best STA/LTA parameters in SDR. The STA/LTA Ratio dialog box can be opened using the Calculate / STA/LTA Ratin menu items.

A command line (DOS Box) utility program called StaLta ( has been written to generate a STA/LTA ratio report similar to the WinQuake feature above. Please see the readme.txt file for more information.