how i can combine keyboard voice to my voice. i am giving the code which i am using.

[y,fs,nbits]=wavread('C:\Users\HP\Desktop\anjali.wav');

sound(y,fs)

t=0:1/fs:length(y)/fs-1/fs;

% original waveform

figure(1)

subplot(3,3,1)

plot(t,y)

title ('time domain waveform of untitled1.wav')

xlabel('time (sec)')

ylabel('amplitude')

%%%%%% keyboard noise

[z,fs,nbits]=wavread('C:\Users\HP\Desktop\keyboard.wav');

sound(z,fs)

t1=0:1/fs:length(z)/fs-1/fs;

% keyboard waveform

figure(2)

plot(t1,z)

title ('time domain waveform of untitled.wav')

xlabel('time (sec)')

ylabel('amplitude')

%%%%%%%%%

y3 = [y(1:500,:); z; y(501:end)];

sound(y3,fs)

t=0:1/fs:length(y)/fs-1/fs;

[Jan]

The question is not clear. Please explain "combine" with any details and describe, if the code is working properly or which problems it has.