OK. I'll try my best to write a guide most people would understand.
My code is attached for your information.
First, note that the first three numbers of 4 octave keys are the same. In my case, it is 024.
Divide 36 characters (A-Z and 0-9) into three blocks. The 1st block consists of A-L; the 2nd block consists of M-X; the 3rd block consist of Y-Z and 0-9. Combine with the first three octave keys. We can make a table matching texts/numbers, code and octave. (As shown in "Initial.jpg")
The table is not final since there is another piece of the puzzle: the interval key.
My interval key is: Perfect Unison (0), Minor Third (3) and Minor Sixth (8 ). We need to shift the text down based on these numbers.
According to one of the email, the first number (0) is the "Transpose key" which affects all blocks. Since it is 0 in my example so we don't have to shift.
The 2nd and 3rd numbers are the "Modulate Keys" which affect block 2 and 3, we need to shift the text down. After that we get the final table (As shown in "Final.jpg") for decoding.
Finally, look at the text and octave keys (start from the 4th number since the first three letters are already used and irrelevant to the text.
The first word in the 1st sentence is
(Eb Ab E C Eb A)
(0 2 0 0 2 2)
Base on the final table, we get (C#=Db, D#=Eb, F#=Gb, G#=Ab, A#=Bb):
(D R E A M S)
Repeat for all lines, we get:
DREAMS 9 OF ASPHYXIATION
RIME OF THREE THE SECURITY MARINE
SERVANT SIX DANCE
RESTLESS NINE WAVES CAPRICE
The numbers are hidden in the texts. So the password is 9369.
