Biomedical Engineering Reference
In-Depth Information
In order for the FFT to be efficient, the number of data samples,
N
, must be a power of two.
If
N
¼
1024 signal samples, the FFT algorithm is approximately 1024
=
log
2
ð
1024
Þ¼
10 times faster
than the direct DFT implementation. If
N
is not a power of two, alternate DFT algorithms are
usually used.
Figures 11.12 and 11.13 show two signals and the corresponding DFT, which was
calculated using the FFT algorithm. The signal shown in Figure 11.12a is a sine wave
6
4
2
0
−
2
−
4
−
6
0
0.05
0.1
0.15
0.2
(a)
Time (sec)
150
100
50
0
0
100
200
300
400
500
(b)
Frequency (Hz)
FIGURE 11.12
(a) 100 Hz sine wave. (b) Fast Fourier transform (FFT) of 100 Hz sine wave.
