Here are two XCMD sets for interfacing HyperCard to MIDI devices:
HyperMIDI 1.1a is a set of XCMDs for sending and receiving MIDI data from
within HyperCard. It comes with several cards demonstrating different methods
of managing MIDI data. One of the features of the XCMDs is the ability to place
graphic sliders on cards. These sliders can be assigned to control any MIDI
parameter.
HyperMIDI is available on many electronic bulletin boards and commercial
software distributors.
A second set of XCMDs for HyperCard and MIDI is MIDI XCMD. This stack is not as
fully featured as HyperMIDI, but will allow the recording and playback of your
MIDI performance.
MIDI XCMD is available on many electronic bulletin boards and commercial
software distributors.