NodeControl
encapsulates in an object a node and an index. this object can be held by a client and have its value set without otherwise having to store the details about where the node's input is.
d = SynthDef("help-NodeControl",{ arg out=0,freq=400;
Out.ar(out,
SinOsc.ar(freq, 0, 0.5)
)
});
y = d.play; // the synth
c = NodeControl(y,1);
c.value = 500;
c.value = 300;