In the old days of vinyl, if you changed the speed, the (musical) pitch of a track changed too. And since the pitch change is more prominent than the bpm change, I am guessing, they called it pitch faders. Since the advent of CDJ’s (well DJ-style CD-players, Denon’s early dual CD-players had pitch controls), there has been an option to change the BPM without the pitch/key changing. This was revolutionary as you could now speed up a track by a higher % than you could on tt’s and not worry about the track starting to sound like donald duck or the smurfs.
These days everyone has key lock on and the faders is effectively a tempo fader that only changes the bpm will the hardware or software keeps the key locked.
Recently mixing in key has become more important. And sometime you want to change the key a bit on a track to match harmonically with the playing track. Yet, you’d still want to be able to match BPM too. So some software now offers the possibility of changing the key (either tru controller mapping – just thinking shift-pitchfader would be nice for that – or thru mouse/keyboard) while still allowing you to change the speed while keeping the altered key.
Hope that answers your question.
Greetinx.
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