Writing midi files from audio data

Hi All,

I have some problems writing midi files. I got an 'output' matrix containing music notes and each note is converted to audio data 'a'. Each 'a' can then be sounded out by soundsc by looping through the notes in the output array. Can anybody help me on how to store all the 'a' in a midi file?

fs=19200;
for x=1:length(output)
    key = tone(output(x));
    a = note10(key,0.5);
    soundsc(a,fs);
end

Thank you for any help you may give in advance!

Andy