Appendix: Midi And Audio Basics - iConnectivity iConnectMIDI2+ Owner's Manual

Appendix: MIDI and audio basics

First came analog synthesizers, then came the digital revolution, at which time
synthesizers were starting to come under digital control. To allow them to communicate
with one another, in 1983 several musical instrument manufacturers agreed upon a
standard: the Multiple Instrument Digital Interface (MIDI).
MIDI is a control language that says things like "play a C3 at xxx velocity, now turn on
the sustain pedal, now turn it off, now stop playing that C3, etc." (Velocity is a measure
of how fast a MIDI key is played, and usually that determines how loud a note is.)
It's up to the receiving device how to interpret these messages, so you could record a
MIDI part (in sequencing, meaning MIDI and audio recording/editing software) from one
keyboard set to a piano sound. Then you could play it back on a harp sound, send it to
a different MIDI instrument playing a guitar sound, transpose the notes, play them back
faster, move them around, make them louder or softer, copy and paste them, and so
on. MIDI is not sound, it is "performance" instructions that receiving instruments and
other devices may use to play sounds (or to do anything else they want, such as
operate lights).
Computers don't accept MIDI plugs – they need a MIDI interface that plugs into one of
their USB ports. The two pairs of MIDI 5-pin DIN ports on your iConnectMIDI 2+ 's rear
panel are the same ports found on every piece of MIDI equipment from 1983 through
today, although the iConnectMIDI 2+ has some very clever processing and routing tricks
up its sleeve.
Digital audio, on the other hand, is the actual sound, not the instructions for playing it. If
you sing or play an instrument into a microphone, the sound waves in the air are
moving a diaphragm that varies the strength of an electromagnet it's attached to (or
varies the capacitance between two membranes) converting the sound to electricity.
When it's recorded – digitized - that sound is measured 44,100 times a second at the
standard CD sampling rate; when it's played back, the process is reversed: the
recorded numbers are used to create a voltage that ultimately drives your speakers,
which move the air so you hear the recording.
Today even an iPhone has enough computing power to run synthesizers that exist only
in software (after all, a digital synthesizer is simply a computer dedicated to one task).
When you use MIDI to trigger a software instrument, the sound is being created digitally
and it's not necessary to digitize it – thus you don't need a standard audio interface with
analog-to-digital conversion for recording and digital-to-analog conversion for playback
on every computing device in your set-up.
So the iConnectMIDI 2+ routes audio that exists inside a computer device (meaning a
computer or a supported iOS device) between two machines. The audio can come from
software instruments and/or it can come from recorded sounds that are on the
computer(s). It can also come from sounds that have been recorded or are being played
live through a regular audio interface on one of the computers.
What's unique about the iConnectMIDI 2+ is that instead of having MIDI interfaces and
audio interfaces on both computer devices – four devices - you just have one box that
routes both MIDI and audio between the machines over USB. That makes it both
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