The FFT provides a computationally fast way to transfer between the time and frequency domains.
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Power density spectrum with data plotted by frequency. Note the general overall steady decrease in power with increasing frequency, interrupted by sharp spikes where the series is periodic. |
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The same power density spectrum with data plotted by period. Note the general overall steady increase in power with increasing period, interrupted by sharp spikes where the series is periodic. |
Table with the data from the plots. Note the general decline in frequency with increasing bin number, but that periods around 12 and 24 hours have anomalously high power, suggesting periodicity in the data at those periods.
Bin Frequency Period Power
1 0.0 infinite 1.348073
3 0.00293 341.333333 0.085273
2 0.00195 512.000000 0.057467
4 0.00391 256.000000 0.030551
5 0.00488 204.800000 0.024552
6 0.00586 170.666667 0.016627
7 0.00684 146.285714 0.010556
8 0.00781 128.000000 0.010149
82 0.08008 12.487805 0.006268
9 0.00879 113.777778 0.006149
10 0.00977 102.400000 0.005995
11 0.01074 93.090909 0.004356
83 0.08105 12.337349 0.004074
43 0.04199 23.813953 0.003910
12 0.01172 85.333333 0.003597
13 0.01270 78.769231 0.003324
40 0.03906 25.600000 0.002679
15 0.01465 68.266667 0.002505
14 0.01367 73.142857 0.002443
42 0.04102 24.380952 0.002357
16 0.01563 64.000000 0.001971
17 0.01660 60.235294 0.001869
18 0.01758 56.888889 0.001701
20 0.01953 51.200000 0.001432
19 0.01855 53.894737 0.001422
81 0.07910 12.641975 0.001408Last revision 2/2/2009