Matlab Record USB Mic

input = dsp.AudioRecorder;
output = dsp.AudioPlayer;

tic;

while (toc < 5)
    stream = step(input);
    step(output, stream);
    plot(stream);
    drawnow;
end

I'm creating a matlab program and I need to record and playback (in real-time) audio input from a USB mic. This is what I have but it does not work. The data coming in is all 0s.