// our UGen patch
SinOsc ugh => dac;

// infinite time loop
while( true )
{
    // randomly choose frequency
    Std.rand2f( 100, 2000 ) => ugh.freq;
    // randomly choose gain
    Std.rand2f( .1, 1 ) => ugh.gain;

    // IMPORTANT: advance time
    120::ms => now;
}