"They don't sell classical music like they used to. Back in the day, if piano titans such as Rudolf Serkin or Artur Rubinstein hit a rough note in the middle of a concerto, engineers would simply patch it up to make it sound perfect. It's called 'sweetening,' and the practice has become such a routine part of the music business that many performing musicians look down on recordings as artificial and illegitimate.
Now for the predictable retro backlash: it has become chic to put the wrong notes back in. The latest Vladimir Horowitz release is a 'cleaned up' version of his 1965 comeback concert in Carnegie Hall. In other words, it does away with all the fixes the original recording engineers patched in from rehearsal tapes. (Luckily, a second unedited tape of the concert was preserved.) For pianists and Horowitz aficionados, this new release boasts not only the quietest digital processing, but the original 'raw' performance without any audio band-aids."