Question

Write a Matlab script that

1. Uses your computer’s audio device to record a single DTMF tone as generated by a cell phone (or an app).

2. Decodes and displays the number associated with the recorded tone.

Answer 1

1. symbol = {'1','2','3','4','5','6','7','8','9','*','0','#'};
[tones, Fs, f, lfg, hfg] = helperDTMFToneGenerator(symbol, false);
helperDFTEstimationPlot1(tones, symbol, Fs, f);

Here is the matlab script for the given question:

2. pc = load('phonecall.mat');

x = pc.x;

fs = pc.fs;

% [S,F,T] = spectrogram(x, 1024, 512, 256*3, fs, 'yaxis');

[S,F,T] = spectrogram(x, 1024, 512*3/4, 256*3, fs, 'yaxis');

Sa = abs(S);

[r, c] = find(Sa >= 30);

Fr = F(r);

Tc = T(c)';

FT = [Tc Fr];

[C, ia, ic] = unique(FT(:,1)); % Find Unique Times

for k1 = 1:size(C,1) % Create Cell Array By Time

FrqTime{k1} = FT(FT(:,1) == C(k1),:); % Time & Frequency Cell

end

original_f = [697 770 852 941 1209 1336 1477]; % DTMF Frequencies

dtmf_dcd = [1 5; 1 6; 1 7; 2 5; 2 6; 2 7; 3 5; 3 6; 3 7; 4 5; 4 6; 4 7]; % Combination Codes w.r.t. ‘original_f’

nbr_map = ['1' '2' '3' '4' '5' '6' '7' '8' '9' '*' '0' '#']; % Number Key Map

for k1 = 1:size(C,1)

freq_dist = abs(bsxfun(@minus, FrqTime{k1}(:,2), original_f)); % Distance Of ‘FrqTime’ Frequencies From ‘original_f’ Frequencies

[~,freq_pos(:,k1)] = min(freq_dist,[],2); % Frequency Positions Of ‘FrqTime’ In ‘original_f’

num_pad(k1) = nbr_map(ismember(dtmf_dcd, freq_pos(:,k1)', 'rows')); % Map To Number Key Pad

end