Performs band limited decimation of a series.
DECILP(series, n, edge, attn)
(out, lpf) = DECILP(series, n, edge, attn)
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series |
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A series or table. |
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n |
- |
An integer factor by which to decimate the series. |
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edge |
- |
Optional. A real, the transition band of the low pass filter Defaults 0.8. |
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attn |
- |
Optional. A real, the attenuation in dB of the low pass filter. Defaults to 70 dB. |
A series.
(out, lpf) = DECILP(series, n, edge, attn) returns the decimated output and the coefficients of the FIR band limiting low pass filter.
W1: integ(gnorm(1000, 1/1000))
W2: decilp(W1, 5)
W3: spectrum(W2, 8*1024)
W4: spectrum(W1, 8*1024);overp(W3, lred);setylog(1,0,1)
The spectrum in W3 is a virtually the first 1/5 of the spectrum of the original data. The length of the output is 1/5 the length of the input.
W2: decilp(W1, 5, 0.95)
Same as above accept the transition band of the low pass filter is narrowed.
DECILP low pass filters a series and then reduces the number of samples by decimation. The band limiting low pass filter preserves the frequency content of the decimated result.
DECILP creates a FIR low pass filter using the Kaiser Window method.
The edge frequencies of the filter are determined by:
Fcut = edge * Fstop
Fstop = Fs / (2 * N)
Where Fs is the sample RATE of the series.
The decimation factor automatically adjusts the sample rate (1/DELTAX) of the resulting series.