There is a well known Medrash (anyone help with the source?) [I think on the Posuk 'Lamnatzeich Al HaShminis - A Sing on the Eight Note Instrument'] that when Moshiach comes the octave will be made up of eight notes instead of seven!

Can anyone point to a source where I can find out if this a new note which is not yet possible to reach or if the scale will just be divided differently into 8 instead of into 7 but will essentially remain the same octave?

Where can I learn more about this new note?