matlab session on pitch extraction

+tony, ronny+

1. I wanted to try another effect before starting with pitch detection algorithms. The one I chose was guitar distortion effect.
   I stumbled upon a very good link: www.musicdsp.org
   There you can find an archive on analysis, effects and some more. It seems that most of the coding is done in C or C#. The distortion effect I tried here is translated to Matlab code.

function [x]=gdist(a,x)
%[Y] = GDIST(A, X) Guitar Distortion
%
% GDIST creates a distortion effect like that of
% an overdriven guitar amplifier. This is a Matlab
% implementation of an algorithm that was found on
% www.musicdsp.org.
%
% A = The amount of distortion. A
% should be chosen so that -1<A<1.
% X = Input. Should be a column vector
% between -1 and 1.
%
%coded by: Steve McGovern, date: 09.29.04
%URL: http://www.steve-m.us
[x,fs] = wavread(x);
k = 2*a/(1-a);
x = (1+k)*(x)./(1+k*abs(x));
wavplay(x,fs);

I also tried another one:

function [output]=fuzzy(sound, amount)
[sound,fs] = wavread(sound);
norms = norm(sound);
output = sound/norms;
amount = (1- amount)/100;
for i = 1:length(output)
if ( output(i) > amount )
output(i) = amount;
end
if ( output(i) < -amount)
output(i) = -amount;
end
end
output = output*norms;
wavplay(output,fs);

Both algorithms are to be found in my folder on ESAT (gdist.m and dist.m)

1. see above
2. I tried to catch a book which was referenced from an article I read (sorry, forgot which one). The book from Roads is called 'the computer music tutorial'. It became a real quest to find it. I didn't yet succeed. I'll keep trying.
3. Order of the day. I'll experiment with pitch extraction: see the rest of this post

• NARGIN; this is used as an indicator of number of input arguments: 'Number ARGuments IN'
• Different methods:
• Pitch determination and voice quality analysis using subharmonic-to-harmonic ratio (http://www.ling.northwestern.edu/~jbp/sun/sun02pitch.pdf )
• Zero crossings
• Autocorrelation
• Maximum likelihood (time or frequency)
  
• Adaptive filter (more than one)
• Super resolution pitch determination
• Harmonic product spectrum
• Cepstrum
• Perceptual pitch detector (http://www-ccrma.stanford.edu/%7Epdelac/154/m154paper.htm )
  
• Worked awhile on the PDA described in another post. I don't really understand how to interpret the resulting output.
  
  This is two times the result f0_values (resp of x2.wav and x1.wav from my thesis folder on ESAT). I have no idea how to interpret it... help me?
• Some other links on pitch detection:
• http://ccrma.stanford.edu/~eberdahl/Projects/Grundfrequenzanalyse/index.html (contains on the first sight a very good tutorial in german )
  
• http://www.dsprelated.com/showmessage/35165/1.php (a discussion on pitch detection for singing voices)
• http://cnx.org/content/m11716/latest/ (m-files on autocorrelation and HPS method)
• http://www.soundmathtech.com/pitch/download/terez_icassp02.pdf (robust pitch determination using non-linear state-space embedding)
• I was hoping to be able to try out some m-files. I even did try the one called fastauto.m, but again I didn't understand the results. More on these tomorrow!