Example 5: Use of the Blackman Window

GUIDE: Mathematics of the Discrete Fourier Transform (DFT). Example 5: Use of the Blackman Window

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Example 5: Use of the Blackman Window

Now let’s apply this window to the sinusoidal data:

% Use the Blackman window on the sinusoid data
xw = [w .* cos(2*pi*n*f*T),zeros(1,(zpf-1)*N)]; % windowed, zero-padded data
X = fft(xw);                                    % Smoothed, interpolated spectrum

% Plot time data figure(6); subplot(2,1,1); plot(xw);
title(‘Windowed, Zero-Padded, Sampled Sinusoid’); xlabel(‘Time (samples)’); ylabel(’Amplitude’); text(-50,1,‘a)’); hold off;

% Plot spectral magnitude in the best way spec = 10*log10(conj(X).*X); % Spectral magnitude in dB spec = max(spec,-60*ones(1,nfft)); % clip to -60 dB subplot(2,1,2); plot(fninf,fftshift(spec),‘-’); axis([-0.5,0.5,-60,40]); grid; title(‘Smoothed, Interpolated, Spectral Magnitude (dB)’); xlabel(‘Normalized Frequency (cycles per sample))‘); ylabel(‘Magnitude (dB)’); text(-.6,40,‘b)’); print -deps eps/xw.eps;

Figure 9.6:Effect of the Blackman window on the sinusoidal data segment.
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