%--
%-- specgram demo idea
%--
format compact
keybd = 0;
Fs = 8000
Fo = 660
T_total = 1.2;
tt = 0:(1/Fs):T_total;
%---
W = 1600;     %-- Total Frequency Deviation
Fch = 990;
chch = dchirp(T_total,W, Fs/W).';
y1 = real( chch.*exp(2i*pi*Fch*tt(1:length(chch))) );
%========================================
Fc = 4;
y1 = vco( sin(2*pi*Fc*tt), [400 700], Fs );
%--
figure(1),   sound(y1,Fs)
  Fmax = Fs/4;
  Nfft = 128;   Nover = 100;
  nn = 1:4:fix(length(y1));
  [B,F,T] = specgram(y1(nn),Nfft,Fmax,[],Nover);
subplot(2,2,1),    imagesc(T,F,db(B,40));
  title(['SINE WAVE MODULATED CHIRP'])
axis xy,  colormap(1-gray)
ylabel('FREQUENCY (Hz)'), xlabel('TIME (sec)')
drawnow,  sound(y1,Fs)
B1 = B; F1 = F; T1 = T;
if( keybd ),  keyboard,  end
%---
%========================================
Fc = 16;
y2 = vco( sin(2*pi*Fc*tt), [400 700], Fs );
%--
figure(1),   sound(y2,Fs)
  Fmax = Fs/4;
  Nfft = 128;   Nover = 100;
  nn = 1:4:fix(length(y2));
  [B,F,T] = specgram(y2(nn),Nfft,Fmax,[],Nover);
subplot(2,2,2),    imagesc(T,F,db(B,40));
  title(['SINE WAVE MODULATED CHIRP'])
axis xy,  colormap(1-gray)
ylabel('FREQUENCY (Hz)'), xlabel('TIME (sec)')
drawnow,  sound(y2,Fs)
B32 = B; F2 = F; T2 = T;
if( keybd ),  keyboard,  end
%---
%========================================
Fc = 64;
y3 = vco( sin(2*pi*Fc*tt), [400 700], Fs );
%--
figure(1),   sound(y3,Fs)
  Fmax = Fs/4;
  Nfft = 128;   Nover = 100;
  nn = 1:4:fix(length(y3));
  [B,F,T] = specgram(y3(nn),Nfft,Fmax,[],Nover);
subplot(2,2,3),    imagesc(T,F,db(B,40));
  title(['SINE WAVE MODULATED CHIRP'])
axis xy,  colormap(1-gray)
ylabel('FREQUENCY (Hz)'), xlabel('TIME (sec)')
drawnow,  sound(y3,Fs)
B3 = B; F3 = F; T3 = T;
if( keybd ),  keyboard,  end
%---
%========================================
Fc = 128;
y4 = vco( sin(2*pi*Fc*tt), [400 700], Fs );
%--
figure(1),   sound(y4,Fs)
  Fmax = Fs/4;
  Nfft = 128;   Nover = 100;
  nn = 1:4:fix(length(y4));
  [B,F,T] = specgram(y4(nn),Nfft,Fmax,[],Nover);
subplot(2,2,4),    imagesc(T,F,db(B,40));
  title(['SINE WAVE MODULATED CHIRP'])
axis xy,  colormap(1-gray)
ylabel('FREQUENCY (Hz)'), xlabel('TIME (sec)')
drawnow,  sound(y4,Fs)
B4 = B; F4 = F; T4 = T;