参考一下这个：

time1=0:1:200;

t1=201:1:400;

time2=401:1:600;

t2=601:1:800;

time3=801:1:1000;

signal1=sin(500*t1); %frequency1 = 500/(2*pi)

plot(t1,signal1);

xlabel('Time (seconds)');

ylabel('Magnitude');

signal2=sin(50*t2); %frequency2 =50/(2*pi)

figure,

plot(t2,signal2);

xlabel('Time (seconds)');

ylabel('Magnitude');

signal=[zeros(size(time1)) signal1 zeros(size(time2)) signal2  zeros(size(time3))];

figure,

time=0:1:1000;

plot(time,signal);

xlabel('Time (seconds)');

ylabel('Magnitude');

x=size(signal);

p=round(x(2)/10);

X=signal;

step_dist=10;

window_length=p;

LENX = length(X);

IMGX = ceil(LENX/step_dist);

if (window_length/2 == round(window_length/2))

IMGY = (window_length/2) + 1;

else

IMGY = ceil(window_length/2);

end

stft_plot = zeros(IMGX,IMGY);

X = [zeros(1,window_length/2) X zeros(1,window_length/2)]; % padding the signal with zeros

WIN = ones(1,window_length);

iter = 0;

for i = 1:step_dist:LENX

iter = iter + 1;

windowing = X(i:(i + window_length - 1));  % making window

signal_window = windowing.* WIN; %y(t)=h(t)*w(n-t)

signalout = abs(fft(signal_window, window_length)); %fft of y(t) gives us stft

stft_plot(iter,:) = signalout(1:IMGY);

end

%sampling_rate=10;

freq = 10;

figure,

imagesc([0:(step_dist):(LENX-1)],[0:(freq):freq*10],stft_plot');

xlabel('Time (seconds)');

ylabel('Frequency (Hz)');

axis('xy')