Musical Instrument Digital Interface (MIDI) is a technical standard that allows multiple electronic devices to synchronize data in real-time.

Musical Instrument Digital Interface (MIDI) is a technical standard that allows multiple electronic devices to synchronize data in real-time.

These could be synthesizers playing the same notes and rhythms...

Musical Instrument Digital Interface (MIDI) is a technical standard that allows multiple electronic devices to synchronize data in real-time.

These could be synthesizers playing the same notes and rhythms...

Or faders on a mixer that move up and down on their own,
controlled by computer software...

Musical Instrument Digital Interface (MIDI) is a technical standard that allows multiple electronic devices to synchronize data in real-time.

These could be synthesizers playing the same notes and rhythms...

Or faders on a mixer that move up and down on their own,
controlled by computer software...

Or lights that blink in time with music.

In other words, MIDI connects all of these devices:

MIDI allows all of these devices to share the same event data:

Events (like notes) are triggered on all devices at the same time.

Use Cases — What is MIDI Used For?

• Realtime synchronization of musical playback on digital instruments, such as keyboards, samplers, and Disklaviers
• Controlling analog instruments, such as Eurorack modular synthesizers
• Synchronizing lighting networks
• Offline sequencing musical notes and rhythms in a musical work
• Editing a note's paramters: rhythm, duration, pitch, loudness, or timbre
• Controlling virtual musical instruments, like plug-ins and VSTs
• Storing a musical score in a small file format

Use Cases — What is MIDI Used For?

Note: Realtime vs. Offline

Realtime: synchronous, instantly rendered within a
fraction of a second in performance

Offline: not synchronous, rendered later,
after careful editing, in a composition

Are MIDI and sound the same thing?

Good question, but... NO!

Sound signals represent pressure waves travelling through air.

Sound can be stored in a digital or analog medium

such as CDs or magnetic tape.

MIDI is a digital format, but does not
transmit recorded sound and is not a signal.

MIDI is like a musical score...

It can store very accurate timing information

about musical parameters like
pitch, rhythm, duration, tempo, and timbre.

MIDI can be stored in small files:
ca. 1000 times less space than audio files!

Like musical scores, MIDI can be stored in simple text files.

MIDI is a very efficient way of
storing musical instructions on a computer.

Is MIDI a computer language?

Good question, but... NO!

Computer languages allow you to construct systems of logic,

and include many classes (i.e., data types),

which can process everything from numbers to letters to sound files.

MIDI, however, is far more basic than that...

Is MIDI a computer language?

MIDI only stores numbers.

These numbers do not represent sound,
but only event triggers.

MIDI cannot represent any other type of data
and only performs one simple task:

Is MIDI a computer language?

MIDI sends binary messages that are interpreted
exactly at the moment they are sent and received...

So, when you depress a key on the keyboard,

or move a fader on the mixer,

instantly a sound is produced,

or a light switches on!

Is MIDI a computer language?

MIDI is therefore not a computer language

and is best thought of as a simple
control protocol.

Many companies designed their own synths,

but these instruments could not communicate...

Korg and Yamaha used one connection format,

but Moog and Roland used another.

In 1981, Dave Smith of Sequential Circuit developed
a message to send pitch data at a 19600 baud rate.

Ikutaro Kakehashi of Roland also worked on a common language
for synthesizers shared by Yamaha, Korg, and Akai.

Roland and Korg began discussing the need for a standard for all
synthesizers at AES ("Audio Engineering Society") in California.

In 1982, the first technical specification was published on the MIDI standard:

• MIDI messages included: Note-On and Note-Off, Pitch Bend, Control Change, Aftertouch, and SysEx.
• A standard 5-pin MIDI cable and port
• IN, OUT, and THRU connections among synthesizers
• Transmission of up to 16 channels per port
• Baud rate of 31250
• Establishment of the IMA (International MIDI Association) to coordinate future work on the standard

So... Where does this mad science come from?!

Each MIDI message includes 2 components:

• a Status Byte: Defines the message type and the channel number.
• and (a) Data Byte(s): Binary numbers formatted for each type of message.

All message components are sent in binary.

Binary: lists containing only digits 0 or 1,
which represent a number or letter

next slide: how to convert a
base 10 number to a binary number...

Types of Messages (3 bits):

Data Bytes

Includes the data formatted for each type of message.

A data byte is 7 binary digits, which can represent
numbers ranging from 0 to 127.

The number of data bytes following a status
byte depends on the type of message sent.

Note-On and Note-Off Messages

Notice that these messages (previous slide) require 2 data bytes:

One number represents pitch while the other represents velocity, or loudness.

Pitch values (0-127) span the range of the orchestra.
MIDI note number 60 is middle C.

Velocity values also range from 0 (silent) to 127 (loudest possible sound).

A velocity value of 0 is considered a Note-Off message.

Note-On and Note-Off Messages

All "notes," then, require 2 MIDI messages:

• a Note-On message, which sends the note's pitch and velocity,
  and which also "starts" the note, and
• a Note-Off message, which "turns off" the corresponding note
  after it is "held" for some duration.

Here is a single note in a piano roll sequencer.

The playhead, moving from left to right, first rolls over point A,
which triggers the Note-On message:

10010001 0111100 1100100 meaning:

status byte + type: Note-On + channel: 1 + MIDI note: 60 + Velocity: 100

After some duration (length of the blue bar), the playhead rolls over point B,
which triggers the Note-Off message:

10000001 0111100 0000000 meaning:

status byte + type: Note-Off + channel: 1 + MIDI note: 60 + Velocity: 0 (silence!)

MIDI File (.mid) Formats

Musical scores can be represented as MIDI files in 2 ways:

• Format 0: All MIDI data is reduced to a single track,
  but parsed by channel number in each MIDI message.
• Format 1: Each channel is represented as a separate track; useful for sequencers, where each instrument is placed on a separate track.

MIDI File (.mid) Formats

.mid files can be opened by many music notation programs

like Finale, Sibelius, MuseScore, LilyPond, or Dorico.

General MIDI: A Standard Sound Bank

A bank of sounds used by all synthesizers,
including software synthesizers available on computers.

Users can call the same instrument represented by a
program change number on any MIDI-compatible instrument.

MIDI Polyphonic Expression (MPE)

The continuous pitch (glissando) of these modern controllers
(on previous slides) are made possible thanks to MPE.

Normally, Pitch Bend messages are sent on all channels at once, but...

MPE allows messages like Pitch Bend to be sent for each individual note...

MIDI Polyphonic Expression (MPE)

In other words, MPE gives each note its own pitch bend,
modulation, pressure, dynamics, and other parameters.

Imagine: each finger or each key acts as its own MIDI controller!

MIDI Polyphonic Expression (MPE)

Like 1982, many instrument builders were trying to address
problems in their own way, without communicating among one another.

Similarly, they needed a standard language.

In 2018, MPE was adopted as a standard for polyphonic
expressiveness by the International MIDI Association.

MIDI Polyphonic Expression (MPE)

Remember how a single DIN cable can carry 16 MIDI channels?

Traditionally, these were used for 16 different instruments,
each with its own Program Change values.

MPE repurposes the use of MIDI channels: each channel is used
for a single note, allowing a polyphony of expressive messaging
per note on a single instrument.

The system permits a maximum polyphony of 15 notes, reserving
one master channel for messages that apply to all notes.

MIDI Over USB Cables

Today, MIDI devices are frequently connected with faster USB cables,
instead of the older and slower DIN cables.

A single USB cable can act as 16 independent MIDI cables,
each with 16 channels,
for a total of 256 MIDI channels.

MIDI Over TRS Cables

For distances over more than just a few meters,
a USB or MIDI cable will experience latency and drops in signal.

A solution has been to use TRS cables.
Like XLR audio cables, TRS can transmit over long distances.

With the growing use of Eurorack analog modular synthesizers,
which normally use small TS patch cables (close to TRS),
it is increasingly common to find MIDI-to-TRS cables
connecting controllers to Eurorack modules.

MIDI Over Ethernet

Ethernet cables (used for internet connections)
are now frequently used to transmit audio.

Now, we also use ethernet cables to transmit
large amounts of MIDI data over large distances,

especially useful when using today's elaborate MIDI interfaces,
which connect many devices in an expansive network.

Advanced MIDI Topics

In our other seminars, we frequently discuss these
and other advanced MIDI issues, like:

• Human gestural control of MIDI
• Microtonal resolution of pitch using MIDI
• Using MIDI values to control custom samplers and microcontrollers
• Mapping MIDI values to control voltage and other synthesis parameters.
• Interfacing MIDI control with sensors and real-world objects
• Broadcasting MIDI over the internet

That's the end!

We hope you learned something useful
to use in your artistic practice!