Just like [Optical illusion][1] happens to our eyes, can this happen to our ears? Consider a well tuned piano. Can we make hearing illusion with music? I show an example with steps: 1. Play a note (or specially chord) on high octaves 2. Play a note or chord on lower octaves than previous one (in general) 3. A second chord be heard like it have more pitch than previous chord. (but in general first chord was on higher octaves.) When I said "in general", it means not all notes have to be lower or higher than other chord. Also two chords should not be too far from each other. I think only 1 or 2 octaves at most. I feel like I heard it before like in _Rachmaninoff Prelude Number 5_ or _Beethoven piano sonata no 32, first movement_ but I'm not sure if that's true or not. Note that this kind of illusion happen to me not because of just playing two chords. I think the music makes the meaning and changes everything and it depends on sentences that was played moment ago. I think that's how it feels. Looking at this line from Prelude Number 5 of Rachmaninoff. [![enter image description here][2]][2] As you can see the red parts have generally higher notes but when you play it, it seems that blue parts have higher pitch. Also another kind of illusion (I wrote this part just to show the case): [![enter image description here][3]][3] I don't know what is the word to describe those blocks so I highlight them in box. After hearing blue boxes, the last note in red box (`G3` I think) is like `G4`. Not a problem with pitch but because you heard `G4` just a moment ago then `G3` feels have the same meaning. But I think that's different from Rachmaninoff example. [1]: https://en.wikipedia.org/wiki/Optical_illusion [2]: https://i.sstatic.net/PBBFE.png [3]: https://i.sstatic.net/qUxTq.png