Operator's Manual
108 WS-OM-E Rev B
Rectangular windows provide the highest frequency resolution and are thus useful for estimating
the type of harmonics present in the signal. Because the rectangular window decays as a (sinx)/x
function in the spectral domain, slight attenuation will be induced. Alternative functions with less
attenuation (Flat Top and Blackman-Harris) provide maximum amplitude at the expense of
frequency resolution. Whereas, Hamming and Von Hann are good for general purpose use with
continuous waveforms.
Window Type Applications and Limitations
Rectangular
These are normally used when the signal is transient
(completely contained in the time-domain window) or
known to have a fundamental frequency component
that is an integer multiple of the fundamental
frequency of the window. Signals other than these
types will show varying amounts of spectral leakage
and scallop loss, which can be corrected by selecting
another type of window.
Hanning (Von
Hann)
These reduce leakage and improve amplitude
accuracy. However, frequency resolution is also
reduced.
Hamming
These reduce leakage and improve amplitude
accuracy. However, frequency resolution is also
reduced.
Flat Top
This window provides excellent amplitude accuracy
with moderate reduction of leakage, but with reduced
frequency resolution.
Blackman–Harris
It reduces the leakage to a minimum, but with reduced
frequency resolution.
FFT Window Filter Parameters
Window Type Highest Side Lobe
(dB)
Scallop Loss
(dB)
ENBW
(bins)
Coherent Gain
(dB)
Rectangular -13 3.92 1.0 0.0
von Hann -32 1.42 1.5 -6.02
Hamming -43 1.78 1.37 -5.35
Flat Top -44 0.01 2.96 -11.05
Blackman-Harris -67 1.13 1.71 -7.53
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