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? because of my horrible English and lack of knowledge about music theory i show 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 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 im not sure if thats 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. sorry i dont know much about music theory terms. so bear with me. Edit: Lokking 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 that blocks so i highlight them in box. after hearing blue boxes...the last note in red box (`G3` i think) is like `G4`. not problem with pitch but because you heard `G4` just a moment ago then `G3` feels have the same meaning. but that's different from Example in Rachmaninoff example. Any ways i think two answers to this question shows another case of illusion but i really appreciated it and it was interesting. ill look more into it. [1]: https://en.wikipedia.org/wiki/Optical_illusion [2]: https://i.sstatic.net/PBBFE.png [3]: https://i.sstatic.net/qUxTq.png