[snorkel]

A whistle or clean guitar string pluck would have one strong tone, and a random banging noise would have many tones overlapping. Typically a digital guitar tuner is just doing a discrete Fourier transform of a sound sample and checking the frequency of the most dominant tone in that sound. Sure it's possible check the signal for tone clarity, such as count how many discrete Fourier components are in the sound sample and their relative strength, where fewer strong components is a cleaner tone.

... but is it really worth it in this case? No, because guitar tuner apps are cheap and plentiful, and electric guitar players use an inline tuner rather than a tuner with a microphone. And for tuners with microphones I get annoyed when the tuner doesn't respond so I prefer a tuner that doesn't try to be too smart and filter out too much.

This is really just a cool example of audio signal processing in javascript (or I suppose we call it "HTML5" nowadays)