Matlab/Octave deMorse.m

function outstring = demorse(wavfile);

%demorse a morsed input wav file

vis_on = 0;

threshold = 0.05;

x = wavread(wavfile);

% half-wave rectify x x2 = abs(x);

% slow-wave filter y = filter(ones(1,20)/20,1, x2);

% threshold (digitize) y z = y > threshold; % z is now effectively our morse signal

if vis_on

  figure(1);
  subplot(3,1,1);
  plot(x, 'r');
  title('original signal');
 
  subplot(3,1,2);
  plot(y);
  title('HWR + Slow-wave filter -> envelope');
  subplot(3,1,3);
  plot(z, 'o', 'MarkerSize', 2);
  title('Digitized Morse signal')
 

end

%zero pad z so we always start with an onset z = [zeros(10,1); z];

% id tones/spaces ----------------------- % --> find changes between 0/1 and 1/0

b = diff(z); % figure(3); plot(b, '.'); % 1: change from 1 to 0 % 0: no change % -1: change from 0 to 1

c = b(b~=0); c2 = find(b~=0);

tokens = -c .* diff([0; c2]); % value == length of token % sign == tone/space

% id shorts/longs -----------------------

% since short/long should be bi-modal dist, a regular average should give % us a good cutoff point to distinguish between the two? (assuming equal % counts of short and long...) % use mean as simple cutoff point; smarter algorithms can get smarter about % this classification if they want to.

% 1: short, 2: long, +: tone, -: space tokens2 = tokens;

% cutoff tones, cutoff spaces; cut_t = mean(tokens2(tokens2>0)); cut_s = mean(tokens2(tokens2<0));

tokens2(tokens > 0 & tokens < cut_t) = 1; tokens2(tokens > 0 & tokens > cut_t) = 2; tokens2(tokens < 0 & tokens > cut_s) = -1; tokens2(tokens < 0 & tokens < cut_s) = -2;

% now tokens 2 is a string of -1s, -2s, 1s, 2s, can trim first known space; % put final endstop at end tokens2 = [tokens2(2:end); -2];

% can drop little spaces, b/c they don't matter when parsing; tokens2(tokens2 == -1) = []; tokens3 = tokens2; tokens4 = {}; ctr = 1; start_idx = 1;

%parse toparse = find(tokens3(start_idx:end) == -2);

for j=1:length(toparse)

  a = toparse(j);
  temp = tokens3(start_idx:a-1);
  tokens4{j} = temp;
  % zeropad for easy comparison
  %tokens4{j} = [tokens4{j}; zeros(length(tokens4{j}), 1)];
  start_idx = a+1;

end

% now tokens4 is de-codeable tokens... proceed to setup lookups % letters code{1} = [1 2 ]; code{2} = [2 1 1 1]; code{3} = [2 1 2 1]; code{4} = [2 1 1]; code{5} = [1]; code{6} = [1 1 2 1]; code{7} = [2 2 1]; code{8} = [1 1 1 1]; code{9} = [1 1]; code{10} = [1 2 2 2]; code{11} = [2 1 2]; code{12} = [1 2 1 1]; code{13} = [2 2]; code{14} = [2 1]; code{15} = [2 2 2]; code{16} = [1 2 2 1]; code{17} = [1 2 1 2]; code{18} = [1 2 1]; code{19} = [1 1 1]; code{20} = [2]; code{21} = [1 1 2]; code{22} = [1 1 1 2]; code{23} = [1 2 2]; code{24} = [2 1 1 2]; code{25} = [2 1 2 2]; code{26} = [2 2 1 1];

% punct code{27} = [1 2 1 2 1 2]; code{28} = [2 2 1 1 2 2]; code{29} = [1 1 2 2 1 1]; code{30} = [2 1 1 2 1];

% numbers

code{31} = [1 2 2 2 2]; code{32} = [1 1 2 2 2]; code{33} = [1 1 1 2 2]; code{34} = [1 1 1 1 2]; code{35} = [1 1 1 1 1]; code{36} = [2 1 1 1 1]; code{37} = [2 2 1 1 1]; code{38} = [2 2 2 1 1]; code{39} = [2 2 2 2 1]; code{40} = [2 2 2 2 2];

decode{1} = 'A'; decode{2} = 'B'; decode{3} = 'C'; decode{4} = 'D'; decode{5} = 'E'; decode{6} = 'F'; decode{7} = 'G'; decode{8} = 'H'; decode{9} = 'I'; decode{10} = 'J'; decode{11} = 'K'; decode{12} = 'L'; decode{13} = 'M'; decode{14} = 'N'; decode{15} = 'O'; decode{16} = 'P'; decode{17} = 'Q'; decode{18} = 'R'; decode{19} = 'S'; decode{20} = 'T'; decode{21} = 'U'; decode{22} = 'V'; decode{23} = 'W'; decode{24} = 'X'; decode{25} = 'Y'; decode{26} = 'Z'; decode{27} = '.'; decode{28} = ','; decode{29} = '?'; decode{30} = '/'; decode{31} = '1'; decode{32} = '2'; decode{33} = '3'; decode{34} = '4'; decode{35} = '5'; decode{36} = '6'; decode{37} = '7'; decode{38} = '8'; decode{39} = '9'; decode{40} = '0';

% compare tokens to tables

out1 = [];

for j = 1:length(tokens4)

   %zero pad temp_tok
   temp_tok = [tokens4{j}; zeros(6 - length(tokens4{j}), 1)];
   for k = 1:length(code)
       if (temp_tok == [code{k}'; zeros(6 - length(code{k}), 1)]);
           out1(j) = char(decode{k});
           %display(decode{k})
       end

   end

   % if didn't find a match
   if isempty(out1(j))
       out1(j) = '_';
   end
  

end

% semi-prettify outstring = 32*ones(2*length(out1),1); outstring(2:2:end) = out1; outstring = char(outstring');

%display('demorsed message:') %display(outstring);