add matlab files

matlab/sample_code_fft.m

@@ -1,16 +1,28 @@
-f = 4000; 
-fs = 22050; 
-fftLength=1024;             %windowlength 
-x =sin(2*pi*f*[0:1/fs:1]);  %makethesinewave 
-ft =fft(x,fftLength);       %doFFT,userect.window 
-ftMag=abs(ft);              %computemagnitude 
+f = 4300; 
+fs =  44100; 
+fftLength=512;             % windowlength 
+x =sin(2*pi*1000*[0:1/fs:1]) + sin(2*pi*f*[0:1/fs:1])  +  sin(2*pi*20000*[0:1/fs:1]);  % makethesinewave 
+ft =fft(x,fftLength);       % doFFT,userect.window 
+ftMag=abs(ft(1:fftLength/2));          % computemagnitude ( half )
 
 % plot the results both in linear and dB magnitudes 
 
 subplot(2, 1, 1), plot(ftMag) 
 title('Linear Magnitude') 
-ylabel('magnitude'), xlabel('bins') 
+ylabel('magnitude'), xlabel('kHz') 
 
+xt = xticks;        % returns the current x-axis tick values as a vector
+fstep = fs/fftLength;       % tick of f axis in f domain 
+xtnew = round(xt*fstep)/1000 ;   % calculate new tick in kHz
+xticklabels(xtnew)      % set new tick labels
+ 
 subplot(2, 1, 2), plot(20*log10(ftMag)) 
 title('dB Magnitude') 
-ylabel('dB'), xlabel('bins')
+ylabel('dB'), xlabel('kHz')
+
+xt = xticks;        % returns the current x-axis tick values as a vector
+fstep = (fs/fftLength);       % tick of f axis in f domain 
+xtnew = round(xt*fstep)/1000;   % calculate new tick in kHz
+xticklabels(xtnew)        % set new tick labels
+
+