I have written a piece that demonstrates the three distinct sounds of the GPO harpsichord. It's as though the keyboardist is playing a harpsichord with three manuals. I believe that a three-manual harpsichord actually existed in the eighteenth and nineteenth centuries. It was scarce and very expensive.
(Yes, I know. Manual Labor is the President of Mexico.) Groan.
This is "Three-Manual Labor". The manual changes occur at 01:22, 02:03, 02:41, 03:20 and 03:56.