(On the other hand if you're talking about the musical instrument the recorder, then why is a treble a middle-pitched instrument a size lower than the common-taught school descant, and with the sopranino and klein gar klein higher in pitch even than that?
By the way, I'm wishing at this point that the voice lower than the treble, the alto, didn't come from the Latin altus, meaning high.)
As I don't actually know the answer to any of these questions, let's deal with the times-three thing first. A team can do the treble by winning three trophies in a season; a darts player can hit a treble by sticking a dart into the smallest numbered ring on a dart board, thereby winning three times the points.
The dartboard is the easiest thing to spot.
To spot a treble voice is easy, too: you just need to get within about, ooh, say half a mile of a first school at play time.
Or if that's too painful you could listen to this:
Spot the Frippet: treble. This word comes from Middle English, from Old French, from Medieval Latin triplum, from Latin triplus.