I'm part of a small theater group looking to add some big sound to our small orchestra. I was wondering if anyone knew of a software package that would allow an artist to record an instrument, say a guitar, then control that recording's playback at show time via the MIDI outputs on a digital keyboard. The software would have to adjust tempo etc based on the way the keyboard is played. Any info would be appreciated!
MIDI Maestro is one professional system designed for this purpose.
If you know someone who is an expert at the Ableton Live environment, you could construct something useful.
There are also several musical theater-related companies that will rent you a turn-key system of computer and samplers with the entire orchestration for a particular hit musical or opera, for augmenting your live orchestra with pre-recorded or MIDI-sequenced performance tracks that can be controlled by a live human conductor tapping out a tempo on a MIDI controller. Those have been around for more than twenty-five years. These companies seem to be rather secretive and proprietary, and I do not know where to look to identify a list of them or find out what systems they can rent you for which musicals or operas, and what it would cost.
The only way that the software can adjust and control the tempo is if it is given a reference beat from the drummer or some other instrument that provides a known quantity of beats per bar. MIDI software can be set up to respond to that kind of trigger. But this won't work in your case, because the keyboard player most likely will not be providing constant rhythmic pulses. Any time the keyboard player pauses, this will throw the software out of whack. You would want to set it up to respond to the drummer, not the keyboardist.