Signal to Noise

Emma Bull's wonderful lyric from The Flash Girls, The Return of Pansy Smith (I guess you could say my walk today was brought to you by this album).

Drinking coffee, have to stay awake and think of you
Aching awfully, knowing my perceptions aren't true
If you were what I've made you, not as your acts betrayed you
How could I keep away?
But things still lead me on, a word and then it's gone
What lives here and what's stray?
Tell me please, what's signal and what's noise?