The Blackman-Harris window coefficients are given by the following formula
where N is the length of the filter and k = 0, 1, …, N – 1.
The Blackman-Harris window is a generalized cosine window (see Hamming window).
An example Blackman-Harris window
Consider a finite impulse response (FIR) low pass filter of length N = 201. The following is the Blackman-Harris window.
Given a sampling frequency of 2000 Hz and a filter cutoff frequency of 40 Hz, the impulse response of the filter with a rectangular window (with no window) and with the Blackman-Harris window is as follows.
The magnitude response of the same filter is shown on the graph below.
Measures for the Blackman-Harris window
The following graph compares the discrete Fourier transform of the Blackman-Harris window and the rectangular window.
The Blackman-Harris window measures are as follows.