PSDENGINE - Two-channel spectrum generator. Similar to the UBIQUITOUS primitive, but additional averaging modes and FFT sizes are possible. This primitive uses the NextMidas FFT libraries for faster speed and a greater number of possible FFT sizes.<I:INPUT_A> - channel A input time domain data <O:PSD_A> - channel A output power spectrum <L:FFT_SIZE> - discrete fourier transform size <A:WINDOW> - name of time-domain window function to apply <D:OVERLAP> - the fraction of the <FFT_SIZE> to overlap adjacent blocks of input time-domain data. The parameter should be > 0 if overlap is desired, = 0 if no overlap with no skipped data is desired, and < -1 if skipped data is desired (-4.0,1.0). <L:AVERAGES> - in BLOCK average mode, this is the number of power spectra to average between output PSD's. In EXPONENTIAL average mode, this is the interval between output PSD's. <I:INPUT_B> - channel B input time domain data <O:PSD_B> - channel B output power spectrum <O:CROSS> - cross spectrum output (FFT_A*) x (FFT_B)
Like UBIQUITOUS, this primitive performs two-channel time-varying spectral analysis using the method of modified, overlapped periodograms.
If any of the output file names is defaulted to blanks, the associated spectrum is not computed. Input files are automatically abscissa registered to ensure that power spectra and the cross-spectrum are computed from the same section of data. This is a must for coherence measurement. The cross spectrum is computed using the conjugate spectrum of the first signal.
The FFT transform size, <L:FFT_SIZE>, can be any size supported by the host platform. For inefficient FFT sizes, a warning is issued and the nearest efficient FFT size is computed and used for output.
See the explain file for WINDOW for more information on available <A:WINDOW> options.
The input files may be complex or scalar. Both inputs must be of the same format (Complex/Real), but the scalar type can be any valid midas type.
The cross spectra output file slot has a real time parameter to choose either the complex cross-spectra, or the complex fft output of either input channel.
Switches: /TL - default input transfer length /SYM - force use of symmetric time-domain window /MODEX - determines initial <O:CROSS> output (1=FFT_A,2=FFT_B,3=CROSS,4=NONE) /WIDCHK - specify the number of input FFT's between widget checks/updates /EXPAVG - specify the exponential averaging coefficient (0.0 to 1.0) /FFTSIZE - return nearest valid FFT size in the supplied result name
Control widgets: 1. M:WINDOW 2. L:AVERAGES 3. M:X OUTPUT 4. L:FFT 5. D:OVERLAP 6. M:AVGMODE 7. F:EXPCOEF
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