[MATLAB数学相关] 求助, 急! 快速傅立叶变换FFT频谱分析问题

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求助, 急! 双音多频信号的检测电话号码 DTMF using fft()
本人最近真在搞一个项目,这个项目是关于信号检测的.
"Touch-tone dialing is one example of how the Fourier analysis is used. The telephone keypad

can be treated as a 4x3 matrix, as shown in Figure 1. Each row and column represents a

frequency."


697 1 2 3

770 4 5 6

852 7 8 9

941 * 0 #

1209 1336 1477



Load the telephone.mat dataset into MATLAB (in the homework #2 folder in VLT). Assume that

the sampling rate for the audio signal was 32768. This has been started in the .m file on VLT.

Finish “AnalyzeTouchtone.m” to identify the phone number being dialed. Turn in the number

and your finished MATLAB code.
双音多频信号(DTMF )的检测电话号码:

必须使用 matlab fft().
Matlab 程序读MATLAB .MAT 文件， 得到输入信号，然后接收端， 用FFT函数进行平谱分析， 从而找到输入信号的有多少个按键·

样本程序如下:
function [] = AnalyzeTouchtone ()


% load the data file touchtone.mat
load touchtone


% Fs (the sampling rate is given as 32768)
Fs = 32768;


% rescale the vector and convert it to double
y = double(y.sig)/128;


% if you look at the data, you can tell there were 11 numbers
% pressed, but on this scale, you cannot tell which ones
n = length(y);
t = (0:n-1)/Fs ;define sampling time period


plot(y);


% continue on and do the fft. identify all of the numbers contained
% in the signal....


end
我该怎样做呢? 能否给个思路?
另外.mat文件中有三个变量，分别是Y, D,z (see attached files)
y, D,z 各代表什么意思呢?
希望高手不吝指点.
多谢.