If you're already familiar with bytebeat, this keyboard mode works similarly to other JS bytebeat software, except t is incremented at a rate relative to the note played on the keyboard, such that the bytebeat function t plays the same pitch as the equivalent sawtooth wave in additive mode.

There is also a second counter, tt, which is incremented so that 1 & tt >> 11 produces quarter notes at the set tempo. This can be used to produce rhythms that will be at the same tempo across all notes. tt is incremented at 8kHz about 113bpm, 11kHz and its multiples at about 163bpm.

The Math object is included, as well as the function int(string, index) for C-style char-to-int indexing and conversion.

If you still have no idea what's going on, here's a more in-depth guide.