Cleverscope CS300 - Page 52

Cleverscope CS300 Reference Manual v2.11
Page 52 www.cleverscope.com ©Cleverscope 2004-2015
FFT Window Characteristics
This table shows the performance of each window in terms of lobe width for a single frequency. Each bin
corresponds to the frequency resolution available.
Window
-3 dB Main Lobe
Width (bins)
-6 dB Main Lobe
Width (bins)
Maximum Side
Lobe Level (dB)
Side Lobe Roll-Off Rate
(dB/decade)
Uniform (None)
0.88
1.21
-13
20
Hanning (Hann)
1.44
2.00
-32
60
Hamming
1.30
1.81
-43
20
Blackman-Harris
1.62
2.27
-71
20
Exact Blackman
1.61
2.25
-67
20
Blackman
1.64
2.30
-58
60
Flat Top
2.94
3.56
-44
20
Example FFT Window selection
The choice of window to use depends on the type of signal being examined, and the desired trade-off between
Frequency resolution, spectral leakage and amplitude accuracy.
The following table gives a first approximation to the best type of window to use:
Signal Content
Best frequency resolution
Best spectral leakage
Best amplitude
accuracy
Sine wave or combination of sine
waves
Hanning
Exact Blackman
Flat Top
Narrowband random signal
(vibration data)
Hanning
Blackman Harris
Blackman Harris
Broadband random
(white noise)
Uniform (None)
Blackman
Uniform
Closely spaced sine waves
Uniform, Hamming
Hamming
Blackman
Excitation signals
(Hammer blow)
Uniform (None)
Unknown content
Hanning