%  This script illustrates basic plotting functions for examining 
%  windows used in DFT and spectral estimation.  This script uses
%  the Tukey window as an example.  Different windows have
%  may have other types of parameters, so code adjustments must be
%  made when inserting other window function into this script.
%
%    written by Kevin D. Donohue (donohue@engr.uky.edu) Sept. 2007


% General window parameters
wlen = 128;  %  Window length
tind = (0:wlen-1)/wlen;  %  Normalized x-axis for plotting
%  Effective sampling frequency
fs = wlen;

%  Tukey window parameters
r1 = .2;   %  Percentage of taper to flat region
r2 = .8;   %  Percentage of taper to flat region

w1 = tukeywin(wlen,r1);
w2 = tukeywin(wlen,r2);

%  Plot window in time
figure(1)
plot(tind,w1,'k--',tind,w2,'r:')
legend({'r=.2', 'r=.8'})
xlabel('Normalized time index')
ylabel('Amplitude')
title('Comparison of windows in time')

%  Compute windowed spectra
pd1 = fft(w1,8*wlen);  % Take DFT
pd2 = fft(w2,8*wlen);   
magpd1 = abs(pd1(1:4*wlen)*fs/wlen);  % Take magnitude of postive frequencies (first half)
magpd2 = abs(pd2(1:4*wlen)*fs/wlen);
faxis = (0:4*wlen-1)/(4*wlen);  %  Normalized frequency axis (1 = Nyquist frequency)

%  Plot spectra on linear amplitude scale
figure(2)
plot(faxis,magpd1,'k--',faxis,magpd2,'r:')
legend({'r=.2', 'r=.8'})
xlabel('Normalized frequency')
ylabel('Linear Magnitude')
title('Comparison of windows in Frequency Linear Scale')

%  Plot spectra on dB amplitude scale
figure(3)
plot(faxis,20*log10(magpd1),'k--',faxis,20*log10(magpd2),'r:')
legend({'r=.2', 'r=.8'})
xlabel('Normalized frequency')
ylabel('dB Magnitude')
title('Comparison of windows in Frequency dB Scale')