MEM power spectrum
command: SPECTRUM <trc-list> <n> [<lo-t> <hi-t>] <lo-f> <hi-f> <f-steps>
Computes power spectrum of traces given by <trc-list>. <n> specifies the number of poles used for the approximation. <lo-t>,<hi-t> selects a time window on the input traces. If omitted the trace window on the current display is used. <lo-f>,<hi-f> specifies the frequency range (in Hz) for the resulting output traces.
<f-steps> is the number of samples on the output traces. For the output trace the horizontal axis gives the frequency in Hz, unless the "/log" qualifier is specified.
parameters
- <trc-list> parameter type: trace list
List of traces to compute power spectrum.
- <n> parameter type: integer
Number of poles (order of approximation).
- <lo-t>, <hi-t> parameter type: real
Time window on input traces. If not specified the current display window is used. If <lo-t> is an astrisk ("*") you can select the window by graphic cursor.
- <lo-f>, <hi-f> parameter type: real
Frequency range to compute the output traces (in Hz).
- <f-steps> parameter type: integer
Number of samples on output traces. The output traces range from <lo-f> Hz to <hi-f> Hz using <f-steps> equidistant sample values.
qualifiers
- /log
The spectrum is computed in logarithmic steps. Be sure that in this case <lo-t> is not zero. For the output trace the horizontal axis gives the logarithm of the frequency (in Hz).
examples
- spectrum all 50 0. 50. .05 3. 200
- computes power spectrum of all traces on display in the time window between 0 and 50 seconds. The output traces range from .05 Hz (20 sec) to 3 Hz using 200 samples.
- spectrum 1 30 *;; .1 4. 300
- computes power spectrum of first trace on display from 10 sec to 4 Hz using 300 samples. The time window on the input trace must be selected by graphic cursor.
- spectrum/log 1 30 *;; .1 100. 300
- Similar to above command except the frequency window and the logarithmic frequency steps.
