Sophie Menter (1846-1918) was an awesome pianist, and probably Liszt's favourite female piano pupil.
You can here her perform Liszt Un Sospiro here:
Interestingly she adds a few bars of music in the middle, and changes the timing at the end. The first time I heard it I thought "Ah yes these 19th century pianists were so free". But it turns out it was the composer himself who authorised the changes to his score, and Ms Menter was being a good student, embracing the changing, developing music.
For more information, let's turn to Rachmaninoff's teacher and cousin, Alexander Siloti. Siloti like Sophie Menter was a pupil of Liszt. In Siloti's edition of this piece (publ Carl Fischer), Siloti notates many extra notes and tweaks which coincide with what Menter plays. Siloti writes p186 "Franz Liszt's playing of this Etude differed greatly from the published version. In fact he changed it so greatly and added so much that was new that I found it impossible to mark every individual change..."
We so often think that music must be a thing, like a statue, static, which we read on the music page and then try to interpret. But it's not like that. It's essence is liquid, like a flowing river. It takes alchemy to conjure up a living interpretation, and courage to depart from the block of ice which is the standard score.
