We covered the connections for a basic MIDI setup with a computer sequencer that uses several MIDI instruments. But how can we hear it?
To hear all of the instruments when there is more than one we will need to connect the audio outputs from all synthesizers, drum machines, samplers and effects units each into a channel on an audio mixer with 1/4 inch audio cables. The output of the mixer can be connected to speakers or headphone so we can hear the audio. In the diagram above we are using powered studio monitor, or speaker with a built-in amplifier. Another output can be connected to an audio recorder so we can capture the playback as a recorded song.
In this scenario we are performing an analog mix direct to two track. This is how many underground or low-budget electronic music was recorded in the 80s and 90s in home MIDI studios or production studios. They would record to stereo cassette, DAT, 1/4 inch stereo or PCM. Another way, which requires more time and equipment, is to record instrument to its own track on a multitrack recorder. A multitrack recorder could be a multitrack tape machine or hard disc recorder. This would allow for the recording of non-MIDI instruments such as guitars, bass, vocals, acoustic drums or any other type of acoustic instrument or non-MIDI instrument. The performer would listen to the multracks as their cue. Each track could be recorded at different times. For example, a single singer could record a three part harmony or someone who plays both guitar and bass could record both, each at a different time on different tracks. The audio from the output of a multitrack recorder could then be fed into other channels of the mixer and mixed to two track. Or audio inputs on an audio interface to be recorded and then mixed in a DAW. A DAW could also record acoustic and non-MIDI instruments and then be mixed "in the box" with the DAW's virtual mixer. The DAW will output a two track audio file which is the mixed song.
Starting in the late 90s it was possible to virtualize synthesisers, samplers, drum machines and effects processing inside the computer DAW. However, hybrid style of production did exist and continues to exist today. Some tracks could be real MIDI instruments, some virtual. Today many productions are "mixed in the box". But in the early days of DAWs they were used as tape machines in that many studio prefered to mix on existing mixing consoles and patching in existing outboard gear. Or an entire DAW session would be transferred to 2 inch 24 track tape so it could be mixed in another studio where the room was tuned better, there were more plentiful options for outboard effects, where the mix engineer prefered to work, or any other number of conceivable reasons.