GTT is an online tool to test your GRUB_INIT_TUNE beforehand.
Just enter a GRUB_INIT_TUNE using the following format:
tempo freq duration [freq duration freq duration...]
Where tempo is the base for all note durations in beats per minute (60 gives
a 1-second base, 120 gives a half-second base, etc.), freq is the frequency
(in hertz) of the sound (set 0 to produce a rest), and duration is the
duration of the sound in a 4/4 bar (meaning 1 is a quarter of a bar and 4 a full
bar).
This project is in a very early stage, so there's a lot of room for improvements. Let me know how GTT can be better.