How can I detect the number pressed from a dtmf tone (.mat) file?

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Elliot Wyllie 2021-5-1

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/818510-how-can-i-detect-the-number-pressed-from-a-dtmf-tone-mat-file

编辑： DGM 2021-5-3

dial_0.mat

I have a DTMF tone that is a .mat file, it just consists of one button press on a telephone and i want to be able to detect the number pressed and output it to the command line. How exactly can I do this?

I posted an example of the .mat file

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Elliot Wyllie 2021-5-1

I have, none of them really worked for me and none used a .mat file

DGM 2021-5-1

在 MATLAB Online 中打开

A mat file is just a container for any sort of variable that matlab can hold. The mat file just contains a vector and a scalar specifying the sampling frequency.

Using this FEX submission I just randomly picked:

https://www.mathworks.com/matlabcentral/fileexchange/10440-dtmf-encoder-decoder

load('dial_0.mat')
thiskey = decode(y',1,fs,numel(y)/fs)

gives

thiskey =
0

Of course, the documentation and parameterization for this function is pretty terrible, but that's some kind of tradition on the File Exchange.

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Answer 1

DGM 2021-5-1

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/818510-how-can-i-detect-the-number-pressed-from-a-dtmf-tone-mat-file#answer_689125

在 MATLAB Online 中打开

Basing off of this example:

https://www.mathworks.com/help/signal/ug/dft-estimation-with-the-goertzel-algorithm.html

% this loads two variables:
% fs -- sampling rate
% y -- signal vector
load('dial_0.mat');
Nt = 205;
source_tones = [697 770 852 941 1209 1336 1477]';
symbols = {'1','2','3';'4','5','6';'7','8','9';'*','0','#'};
k = round(source_tones/fs*Nt);  % Indices of the DFT
estim_f = round(k*fs/Nt);      % Frequencies at which the DFT is estimated
tone = y(1:205);
% Estimate DFT using Goertzel
ydft = goertzel(tone,k+1);
% find the two most powerful frequencies
[~,sourcetoneidx] = sort(abs(ydft),'descend');
sourcetoneidx = sourcetoneidx(1:2);
% sourcetoneidx should contain one index from
% each group of source tones (first four, last three)
row = min(sourcetoneidx);
col = max(sourcetoneidx)-4;
% look up the symbol in the table
thissymbol = symbols{row,col}

gives

thissymbol =
    '0'

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DGM 2021-5-1

编辑：DGM 2021-5-1

在 MATLAB Online 中打开

Yes. The example I linked to on the File Exchange uses FFT. Just download it and open decode.m. It's a bit of a mess, but it has comments explaining the steps.

EDIT: it really is kind of a mess. I stripped it down and added some comments so it makes more sense:

load('dial_0.mat');
	
d = numel(y)/fs;
% fft analyze of the frequency coded signalvector
signal=abs(fft(y));                        
% Analyze to the half sampling rate, because the frequencies after are
% not interesting for analyze. They were created by sampling the signal 
x=1:(fs/2)*d;
% plot the spectrum to see the peaks
plot(signal(x))
% maximum of the array
[~,idx]=max(signal(x));
% frequency 1 
f1=(idx/d)-1;
% we no longer want to consider frequencies close to this peak
% set adjacent samples to 0 
idx=idx-10:idx+10;
signal(idx)=0; 
% next maximum of the array
[~,idx]=max(signal(x));
% frequency 2 
f2=(idx/d)-1;
% sort hi/low frequencies
if f1>1000
    var=f1;
    f1=f2;
    f2=var;
end
% include frequency tolerance and sort the key frequencies (the actuall  
% tolerance are at with time: >= 0.0499 s and sampling rate: 3300Hz)
if ((f1>692) && (f1<720))
    row=1;
elseif ((f1>765) && (f1<800))
    row=2;
elseif ((f1>847) && (f1<880))
    row=3;
elseif ((f1>936) && (f1<960))
    row=4;
end
if ((f2>1204) && (f2<1240))
    col=1;
elseif ((f2>1331) && (f2<1360))
    col=2;
elseif ((f2>1472) && (f2<1500))
    col=3;
elseif ((f2>1628) && (f2<1660))
    col=4;
end
% look up the symbol associated with this DTMF pair
symbols = {'1','2','3','A';'4','5','6','B';'7','8','9','C';'*','0','#','D'};
thiskey = symbols{row,col}

The peak-finding and binning routine can probably be cleaned up significantly, but the basic idea is there. Do FFT, find the peaks, do symbol lookup.

EDIT:

Well, I did say it could be cleaned up.

load('dial_0.mat');
% do fft
signal=abs(fft(y));   
d = numel(y)/fs;
sourcetones = [697 770 852 941 1209 1336 1477 1633];
tonewindows=zeros(size(signal));
tonepower = zeros(8,1);
for f=1:numel(sourcetones)
    tonepower(f) = sum(signal(round(d*(sourcetones(f)+(-20:20)))));
    tonewindows(round(d*(sourcetones(f)+(-20:20))))=1000;
end
% plot the signal and sampling windows
x=round((500:2000)*d);
plot(signal(x)); hold on;
plot(tonewindows(x))
% same thing as in the first example
[~,sourcetoneidx] = sort(tonepower,'descend');
sourcetoneidx = sourcetoneidx(1:2);
row = min(sourcetoneidx);
col = max(sourcetoneidx)-4;
% look up the symbol associated with this DTMF pair
symbols = {'1','2','3','A';'4','5','6','B';'7','8','9','C';'*','0','#','D'};
thiskey = symbols{row,col}

This approach is more like the DFT example. Instead of trying to sort out peaks, just look where you expect peaks to be and find the two most powerful ones.

Elliot Wyllie 2021-5-1

编辑：Elliot Wyllie 2021-5-1

Jeez that stuff goes right over my head, im a bit of a beginner when it comes to coding and signal processing. Im assuming I would have to rework all that code to fit the .mat file because decode file seems to work based off the encode file.

DGM 2021-5-1

编辑：DGM 2021-5-3

At this point, I wouldn't worry too much about using the FEX code directly. Like I said, it's a mess and requires the user input a bunch of extraneous parameters because it was probably designed only to do a particular thing (yes, probably it was just made to recycle the tones generated by the encoder).

That's why I cleaned it up and reduced it to a simplified script that takes the mat-file as given. No parameters needed, just a filename (assuming your mat-files all contain variables called fs and y).

EDIT:

I cleaned up my suggested code and made a encoder/decoder set of tools. Hopefully these will be a better resource to the next person that has the same task:

https://www.mathworks.com/matlabcentral/fileexchange/91500-simple-dtmf-encoder-decoder

There's no special toolboxes needed, and it should be compatible back to at least R2009b.

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