Originally Posted by
AAJH
I'm no expert in Bootlegs or Mash ups, but I would say change the acapella to match the key of the instrumental.
Okay so, Semitones are measured in Cents, every 100 Cents is one Semitone & 1200 Cents is one Octave.
For example: If your instrumental is in the key of G Major and your acapella is in the key of C Major you would need to pitch up the vocal by 700 Cents & then the acapella would be in key with the instrumental.
Or, pitch down the vocal by 500 Cents & then the acapella would be in key with the instrumental.
Why 700 Cents? Because there are 7 semitones (ascending) between C and G.
Why 500 Cents? Because there are 5 semitones (descending) between C and G.
But, if your instrumental is in the key of G Major & your acapella was in the key of C Major you wouldn't necessarily need to change the pitch, because these keys work well together harmonically.
If you need any more info, just ask :)
Also, if I've made a mistake, please correct.