%PressKeyDown.m
function Signal=PressKeyDown(handles,key)
Signal=dtmf(key);
sound(Signal,8000);  %利用聲卡播放撥號音
set(gcf,'CurrentAxes',handles.TimeFig);
plot(Signal);grid
Spectrum=fft(Signal);
Spectrum=fftshift(Spectrum);    %計算信號的頻譜
N=length(Spectrum);
nStep=(2*pi)/(N-1);
w=-pi:nStep:pi;
set(gcf,'CurrentAxes',handles.FrequencyFig);
plot(w/(2*pi)*8000,abs(Spectrum));grid    %畫信號的頻譜圖
axis([-2000,2000,0,200]);
xlabel('單位：Hz');