Applying the Blackman Window
Now let's apply the Blackman window to the sampled sinusoid and look at the effect on the spectrum analysis:
% Windowed, zero-padded data: n = [0:M-1]; % discrete time axis f = 0.25 + 0.5/M; % frequency xw = [w .* cos(2*pi*n*f),zeros(1,(zpf-1)*M)]; % Smoothed, interpolated spectrum: X = fft(xw); % Plot time data: subplot(2,1,1); plot(xw); title('Windowed, Zero-Padded, Sampled Sinusoid'); xlabel('Time (samples)'); ylabel('Amplitude'); text(-50,1,'a)'); % Plot spectral magnitude: 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]); title('Smoothed, Interpolated, Spectral Magnitude (dB)'); xlabel('Normalized Frequency (cycles per sample))'); ylabel('Magnitude (dB)'); grid; text(-.6,40,'b)');Figure 8.6 plots the zero-padded, Blackman-windowed sinusoid, along with its magnitude spectrum on a dB scale. Note that the first sidelobe (near


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Hann Window Spectrum Analysis Results
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Bandlimited Interpolation of Time-Limited Signals