Each line of music is a famous piece, but with some egregiously wrong extra notes added in certain positions. These wrong notes are the first digits of a famous mathematical constant, with one or two wrong extra digits:
| Piece | Extra Notes | Constant | Extra Digits | Letter |
|---|---|---|---|---|
| Beethoven's Fur Elise | 314151892 | pi | 18 | R |
| Mozart's Eine Kleine Nachtmusik | 141452135623 | sqrt(2) | 5 | E |
| Grieg's In The Hall of the Mountain King | 693147180135 | ln(2) | 13 | M |
| Chopin's Funeral March | 577215616 | Euler-Mascheroni constant gamma | 1 | A |
| Bach's Prelude in C | 1618019339 | golden ratio | 19 | S |
| Mendelssohn's Violin Concerto | 2712082818 | e | 20 | T |
| Rossini's William Tell Overture | 120205659031 | Apery's Constant zeta(3) | 5 | E |
| Pachelbel's Canon | 142857141828571 | 1/7 | 18 | R |
(Note that the instrument in the William Tell Overture is an A Clarinet, which hopefully explains any discrepancies between the written notes and the recording.)
Reading out the letters spells the answer REMASTER.