gistfile1.matlab

%%%
%  Dual Tone Multi Frequency Decoder
%  ENEL440 Assignment 1, 2010  
%   John Howe                 
%%%

clear; clc;

% Array of DTMF frequencies f1 - f8 numbered as so:
%            f5  f6  f7  f8
keypad = [  '1','2','3','A'; % f1
            '4','5','6','B'; % f2
            '7','8','9','C'; % f3
            '*','0','#','D'];% f4
DTMF = [697, 770, 852, 941, 1209, 1336, 1477, 1633];
numRowFreqs = 4;
numColFreqs = 4;

% Desired parameters for each FIR filter.
passBandwidth = 10;         % Hz
transitionBandwidth  = 100;  % Hz
stopbandAttenuation = 18;   % dB

% Parameters used for DTMF detection.
sensitivity = 0.5; % Dominance one frequency must have to be considered a tone
subSampleLength = 20; % Size of sample to be analysed at once (in ms)
sampleFreq = 3700; % Sample rate for input data in Hz

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%  Configuration ends here. %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

ls *txt
s = input('Enter test signal filename (inside single quotes),\notherwise default group20.txt will be used: ');
try 
    importdata (s);
catch
    fprintf ('Using group20.txt\n');
    importdata 'group20.txt';
end

samples = ans - mean (ans);
% Approximation for the number of taps to achieve the desired filter parameters
numTaps = round ((sampleFreq * stopbandAttenuation) / (22 * transitionBandwidth));
nyquistFreq = sampleFreq /2;

fprintf ('Generating FIR filters using %d taps with a %dHz transition\n bandwidth and a %ddB stopband attenuation.\n', numTaps, transitionBandwidth, stopbandAttenuation);

% Calculate the FIR filter coefficients for each DTMF frequency using the
% Parks-McClellan optimal equiripple FIR filter design.  
for i = 1 : size (DTMF, 2)
    % F is a vector of frequency band edges in pairs, in ascending order
    % between 0 and 1. 1 corresponds to the Nyquist frequency or half the
    % sampling frequency. At least one frequency band must have a non-zero
    % width.
    Fst0 = 0;% Filter start
    Fst1 = (DTMF(i) - transitionBandwidth) / nyquistFreq;% First Stopband Frequency
    Fp1 = (DTMF(i) - passBandwidth/2) / nyquistFreq;% First Passband Frequency
    Fp2 = (DTMF(i) + passBandwidth/2) / nyquistFreq;% Second Passband Frequency
    Fst2 = (DTMF(i) + transitionBandwidth) / nyquistFreq;% Second Stopband Frequency
    Fst3 = 1;% Filter end
    F = [Fst0, Fst1, Fp1, Fp2, Fst2, Fst3];

    % A is a real vector the same size as F which specifies the desired
    % amplitude of the frequency response of the resultant filter B.
    A = [0, 0, 1, 1, 0, 0]; % Here we are using a bandpass filter

    % B=FIRPM(N,F,A) returns a length N+1 linear phase (real, symmetric
    % coefficients) FIR filter which has the best approximation to the desired
    % frequency response described by F and A in the minimax sense.
    FIR (i, :) = firpm (numTaps-1, F, A);
end

fprintf ('Analysing data using a %dms chunk size.\n', subSampleLength);

% The sampled signal is split into sub-samples the same width as the FIR
% filter. Each of these is analysed to find which key (if any) has been
% pressed. 
subSampleStart = 1;
totalSamples = size (samples,2);
hits = 0;
subSampleCount = round (subSampleLength * sampleFreq / 1000);
while subSampleStart <  (totalSamples - subSampleCount)
    colFreq = 0;
    rowFreq = 0;
    subSample = samples (subSampleStart:subSampleStart + subSampleCount);
    % Each sub-sample is passed through each of the filters.
    for i = 1 : numRowFreqs
        rowSubSample (i, :) = filter (FIR (i,:), 1,  subSample);
        rowEnergy (i) = round (sum (rowSubSample (i, :).^2));
    end
    for i = 1 : numColFreqs
        colSubSample (i, :) = filter (FIR (i + numRowFreqs,:), 1,  subSample);
        colEnergy (i) = round (sum (colSubSample (i, :).^2));
    end

    % To test if a tone is present in just one of the frequencies in a bank it
    % must contain more energy than in all the bank's other frequencies combined.
    totalColEnergy = sum (colEnergy);
    totalRowEnergy = sum (rowEnergy);
    for i = 1 : numRowFreqs
        if (colEnergy (i) / totalColEnergy) > sensitivity
            rowFreq = i;
        end
    end
    for i = 1 : numColFreqs
        if (rowEnergy (i) / totalRowEnergy) > sensitivity
            colFreq = i;
        end
    end

    % For a button to be pressed both a row and column must be active
    if colFreq & rowFreq
        thisKey = keypad (rowFreq, colFreq);
        % This prevents multiple detections of the same key press
        if hits == 0
            hits = hits + 1;
            sequence (hits) = thisKey;
        elseif (thisKey ~= sequence (hits)) && (lastKeyPress)
            hits = hits + 1;
            sequence (hits) = thisKey;
        end
        lastKeyPress = 1;
    else
        lastKeyPress = 0;
    end
    % increment to next block of samples
    subSampleStart = subSampleStart + subSampleCount; 
end

% Display the DTMF sequence (if one was detected)
if hits
    fprintf ('Received the following sequence of keys: %s\n', sequence);
end