how to split signal in dtmf program

I was doing decoding phone number project using FFT algorithm, i do not know how to set up an rule for setting an threshold to split signal into several segment, and also how to do it in matlab code, so can anyone help me please, here is what i did right now.

[y,Fs,bits] = wavread('PhoneNumberA_2013.wav');

Nsamps = length(y);

t = (1/Fs)*(1:Nsamps)          %Prepare time data for plot

%Do Fourier Transform

y_fft = abs(fft(y));            %Retain Magnitude

%y_fft = y_fft(1:Nsamps/2);      %Discard Half of Points

f = Fs*(0:Nsamps-1)/Nsamps;   %Prepare freq data for plot

%Plot Sound File in Time Domain

figure(1)

plot(t, y)

xlabel('Time (s)')

ylabel('Amplitude')

title('PhoneNumberA frequency in Time Domain')

%Plot Sound File in Frequency Domain

figure(2)

plot(f, y_fft)

axis([0,1800 0 600])

%xlim([0,2000])

%ylim([0,800])

xlabel('Frequency (Hz)')

ylabel('Amplitude')

title('PhoneNumberA frequency in Frequency domain')

i am sorry because i do not how to upload my image, but i am pretty sure till now the code i upload is correct, please help me~

thank you

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

Answer 1

[Youssef Khmou]

hi MU,

in DTMF ( Dual Tone Multi Freqency) the phone number is composed of 11 digits, so you need to divide the length of y or Nsamps according to your code into 11 equal segments y1,y2,.......y11 and for each yi compute the Amplitude spectrum ,extract the two frequencies (697 770 852 941 1209 1336 1477 ) Hz and use conditioning test to recognize the digits :

 n=floor(Nsamps/11);
 %construct a matrix that contains the segments  A(n,11) :

 A=zeros(n,11);
 A(:,1)=y(1:n);
 A(:,2)=y(n+1:2*n);
 A(:,3)=y(2*n+1:3*n);
 %.....
 A(:,11)=y(10*n+1:end);
 %Now  compute the spectra : FFT(A(:,1)..................A(:,11)

 % Extract the frequencies and store them in B(11x2) matrix such that every
 % row contains one DTFM 
 % use conditioning test

I hope that helps

[Walter Roberson]

In North America, DTMF phone numbers can be:

• one digit, (0) for operator
• three digits, such as 411 (directory assistance) or 611 (repairs) or 911 (emergency)
• seven digits, for local phone calls in the same area code
• eight digits, (1 followed by 7 digits) for long distance phone calls in the same area code
• ten digits, (3 digits of area code followed by 7 digits), for local phone calls to different area codes (larger areas sometimes need multiple area codes for the same city)
• eleven digits (1 followed by 3 digits of area code followed by 7 digits), for long distance calls to different area codes within North America)
• eleven digits (1 followed by 3 digits of country code followed by 7 digits), for international calls to most Caribbean countries
• at least 5 digits (011 followed by at least 1 digit of country code, followed by a possibly variable number of digits to reach a phone number in that country) for other international calls

[Youssef Khmou]

hi, alright, anyway he can define the number by counting the peaks in the time domain .