// patch
Step step => Gain sum => SinOsc c => dac;
// add the modulator to the step at 'sum'
SinOsc m => sum;

// carrier freq
440 => step.next;
// modulation freq
200 => m.freq;
// index of modulation
220 => m.gain;

// go!
while( true )
{
    1::second => now;
}