1. The MIDI Standard A

2. Overview What is MIDI? Brief history of MIDI How does MIDI work?
Short Example
MIDI Files and Connections
Timing Issues
Advantages and Disadvantages A

3. What is MIDI? MIDI stands for Musical Instrument Digital Interface
Standard that specifies the hardware interface and the data format of electronic instruments and audio systems
Intended to connect to musical instruments, computers, and related audio devices
Small file size, large range of instruments, and easy to modify
MIDI is like sheet music, and sound cards are the instrument and musician A
Picture
Define channels

4. Why does MIDI exist?
Before MIDI (early 1980s) there was no standard for communication between electronic musical instruments
different manufacturers means different standards
possibly trying to link analog and digital devices to each other
limiting musicians ability to perform with many different machines
Roland, a Japanese musical instrument company, proposed making a standard
Wanted it to be simple and small
The music community, specifically Roland, Oberheim Electronics, Sequential Circuits, Yamaha, Korg and Kawai, then created MIDI A

5. Basic Vocabulary Channel: synonymous to slave select
Each MIDI device usually has several channels
Think of a channel as an individual capable of playing many instruments and switching between them
Program/Patch: the “instrument” that the channel will be imitating (e.g. electric guitar, drum, bass, etc)
MIDI Instrument: MIDI defines this as any MIDI device
Include sequencer, synthesizer, drum machine, etc. S

6. MIDI Communication Protocol
MIDI messages are sent over asynchronous serial at baud
Start bit, 8 data bits, stop bit
10 bits over a period of 320 mircoseconds per serial byte
The messages are broken up into Status bytes and Data bytes
Status byte is sent first, followed by each data byte S
picture
From MIDI 1.0 Specification

7. MIDI Communication Protocol
Upper 4 bits of the Status describe the command (MSB is always 1)
Lower 4 bits are the channel number
The structure of the data bytes is dependent on the command
Instructions can be sent in real-time or stored in a MIDI file (depending on device) S

8. Some Important MIDI messages
NoteOn - 0x9M 0xNN 0xNN
Plays a note with specific pitch and attack (volume)
NoteOff - 0x8M 0xNN 0xNN
Turns off a note on a channel
ControlChange - 0xCM 0xNN
Knob, switch, pedal, etc.
Generated when state of a controller changes
ProgramChange - 0xBM 0xNN
Used to switch program on a specified channel
System Exclusive Messages
Unique to specific MIDI devices (determined by the manufacturer)
M - channel select bits
N - depends on input J

9. MIDI Note Range Zero-indexed from C-1 (note 0) to G9 (note 127)
This goes beyond the range of an 88-key piano
C-1 is approximately 8 Hz -- below the human hearing range
G9 is approximately 12.5 KHz -- within the typical human hearing range J

10. How does a MIDI synthesizer work?
When a key is pressed, a “NoteOn” message is generated based on the key
That message is sent over serial to a microcontroller
The microcontroller reads the message and play audio from a stored bank of samples
When the key is released, a “NoteOff” message is sent in the same way
Pedals, pitch wheels, knobs, and other devices can be used to send “ControlChange” messages that can modify the sound, select what instrument is being played, etc. J

11. Example MIDI Sequence Status Data1 - Pitch Data2 - Attack
animations
Example from

12. Standard MIDI File (SMF)
Standardized file formats to save sequences that can then be played back on other MIDI devices
Header contains information about the file
arrangement track count, tempo, and format
Type 0, 1 and 2 files
Type 0: single track of entire performance
Type 1: multitrack to be played back simultaneously
Type 2 (rare): multiple arrangements, each arrangement in own track to be played sequentially
Popular way to distribute music in Europe and Japan in the 1990s C

13. MIDI Connections 180° five-pin DIN connector
Typically only 3 pins used
USB connectors also now common
MIDI in, thru and out
In: provides input from MIDI controller
Thru: output signal that provides copy of the MIDI in (daisy chaining)
Out: provides output to another MIDI device, perhaps a synthesizer
Image sources: Pack/dp/B009GUP5SW, MIDI 1.0 Specification C
Clarify USB connection

14. C
“To avoid ground loops, and subsequent data errors, the transmitter circuitry and receiver circuitry are internally separated by an opto-isolator (a light emitting diode and a photo sensor which share a single, sealed package).”
MIDI 1.0 Specification

15. https://whitefiles.org/b1_s/1_free_guides/fg1mt/pgs/h15g.htm C

16. Timing Issues 3 Bytes of data takes around 1ms to send
Sending the same info to all 16 channel can be a delay of 16ms
Only one note can start or stop per MIDI instruction
What if you want more than one to start or stop simultaneously?
Some MIDI devices use timestamps to specify in advance when notes should stop or start. Using timers and interrupts, these instructions can be executed with significantly less delay!
Length of cords can cause delay
MIDI specifies maximum of 50 ft A

17. How has it changed over the years?
General MIDI (1991)
Further specifications for MIDI-compatible instruments
Must support 16 simultaneous channels
Must support multiple simultaneous notes on each channel
Defines the instrument mapped to each of the 128 possible patch numbers
Also General MIDI Level 2 added a couple features
Manufacturers have created their own specific supersets of MIDI
Most just add support for their own patches
Roland GS (1991)
Yamaha XG (1994) A

18. MIDI Applications
Primary application is based on audio and audio equipment
Digital synthesizers and sequencers
Digital Audio Workstations
Effects units
Lighting systems
Video game music
Early computer audio J

19. Advantages/Disadvantages
File sizes are much smaller than audio files
Only contain instructions on how to play audio
Multiple devices can be linked together
MIDI sequences can be edited in ways that audio files cannot, such as changing pitch of a section
Disadvantages:
MIDI specification only describes how MIDI devices communicate
Not what they do: slightly different sounds, different capabilities across devices
Quality of sound is limited by playback device
Most MIDI instruments have a different sound from their real instrument counterpart
Can’t store vocals - still an audio file J

20. Conclusion
MIDI is an excellent tool for communicating with or between musical instruments
It has a large set of instructions that give plenty of versatility
The communication protocol it uses is very simple
MIDI is very widely-adopted
On the other hand, vendor-specific supersets of MIDI can get confusing fast
Sound quality cannot match actual recordings or real instruments J

21. Further reading
The MIDI 1.0 Specification:
Requires a free account to download
Summary of MIDI Messages:

22. Questions?