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DADiSP Worksheet Functions > Function Categories > Generated Series > GBLACKMAN
Generates a 3 term Blackman Window.
GBLACKMAN(N, spacing, "sym")
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N |
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An integer, the number of points to generate. |
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spacing |
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A real, the spacing (delta x) between points. |
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"sym" |
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Optional. A string, the symmetry flag.
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A series.
W1: gblackman(100, .01)
generates a 100-point symmetric 3 term Blackman window using the following formula:
where n is the nth point (1 <= n <= N) and N is 100, the number of points. The spacing between samples is set to 0.01.
W2: gblackman(100, 0.01, "periodic")
Creates a 100 point periodic Blackman window that conforms to the ISO 18431-1 standard.
where n is the nth point (1 <= n <= N) and N is the number of points to generate. The spacing between samples is set to 0.01.
The "sym" flag controls the window symmetry as follows:
"Symmetric" sets the last point to be the same value as the first point. For an N point symmetric window, a N-1 point periodic window is effectively created and the Nth point is set to the same value as the first point.
"Periodic" or "iso" creates a periodic window function useful in spectrum analysis applications. "Periodic" or "iso" conforms to the ISO 18431-1 standard for windowing functions.
The Hamming, Hanning, Flattop and Blackman windows are part of the family of cosine window functions. The ISO 18431-1 standard periodic form of these windowing functions are defined by:
where K is the number of window coefficients and N is the length of the window. The symmetric form of the window can be constructed by setting N to N-1.
For the Blackman window:
Use the BLACKMAN function command to automatically create and multiply a Blackman window with a series. For example:
blackman(W1)
multiplies Window 1 with a Blackman window of the same length and spacing as the series in W1.
See GBLACKMANHARRIS to generate a 4 term Blackman-Harris window.
Blackman, Blackman-Harris, Flattop, Hamming, Hanning and Kaiser Windows are useful in creating FIR filters and in preprocessing series for FFT calculations.
GBLACKMAN can also be invoked as GBLCKMAN.