Looks like Google Chrome 66, and on windows 7. I'd wager it's the new auto play being funky.

Went to firefox instead and was able to go through it. Again, very cool. =)

It absolutely is that. I experienced the problem, captured

    options.context = new window.AudioContext();

from index.js at line 224, and then just bound a user-action (I went with document.body.addEventListener('click')) and used that to call options.context.resume().

After which point, it was cool. =)

Not OP, but chiming in to say that on Waterfox on Windows 10, the initial guitar that is supposed to be out of tune is perfectly in tune (I'm a guitarist and it was obvious). I scrolled down to the tuning part anyway, and moving the knobs changed the frequency display but never changed the sound of the string being tuned.