MIDI

MIDI (; Musical Instrument Digital Interface) is a technical standard. It describes a communications protocol, digital interface, and electrical connectors. It connect a large variety of electronic musical instruments, digital devices for playing, editing, and recording music. 
A MIDI recording is not an audio signal. It is more like a piano roll, identifying the pitch, start and stop time and other properties of each individual note.
The market stabilized at the same time. It makes MIDI came, and computers became a viable option for music production.