The MIDI Standard 1 Overview What is MIDI

The MIDI Standard 1

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

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 https: //store. djtechtools. com/products/midi-fighter-64 3

Why does MIDI exist? ● Before MIDI (early 1980 s) 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 4

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. 5

MIDI Communication Protocol ● MIDI messages are sent over asynchronous serial at 31250 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 0 - 2 Data bytes ● Status byte is sent first, followed by each data byte From MIDI 1. 0 Specification 6

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) http: //properlydone. org/Midi. Theory/midi_messages. htm 7

Some Important MIDI messages ● Note. On - 0 x 9 M 0 x. NN ○ Plays a note with specific pitch and attack (volume) ● Note. Off - 0 x 8 M 0 x. NN ○ M - channel select bits N - depends on input Turns off a note on a channel ● Control. Change - 0 x. CM 0 x. NN ○ ○ Knob, switch, pedal, etc. Generated when state of a controller changes ● Program. Change - 0 x. BM 0 x. NN ○ Used to switch program on a specified channel ● System Exclusive Messages ○ Unique to specific MIDI devices (determined by the manufacturer) 8

MIDI Note Range ● Zero-indexed from C-1 (note 0) to G 9 (note 127) ● This goes beyond the range of an 88 -key piano ● C-1 is approximately 8 Hz -- below the human hearing range ● G 9 is approximately 12. 5 KHz -within the typical human hearing range 9 http: //global. oup. com/us/companion. websites/fdscontent/uscompanion/us/static/companion. websites/9780199922963/Chapter 7. html

How does a MIDI synthesizer work? ● When a key is pressed, a “Note. On” 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 “Note. Off” message is sent in the same way ● Pedals, pitch wheels, knobs, and other devices can be used to send “Control. Change” messages that can modify the sound, select what instrument is being played, etc. 10

Example MIDI Sequence Status Data 1 - Pitch Data 2 - Attack Example from http: //www. music-software-development. com/midi-tutorial. html 11

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 1990 s 12

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: https: //www. amazon. com/Monoprice-108532 -Cable-Plugs-2 -Pack/dp/B 009 GUP 5 SW, MIDI 1. 0 Specification 13

MIDI 1. 0 Specification 14

https: //whitefiles. org/b 1_s/1_free_guides/fg 1 mt/pgs/h 15 g. htm 15

Timing Issues ● ● 3 Bytes of data takes around 1 ms to send Sending the same info to all 16 channel can be a delay of 16 ms 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 http: //expressiveness. org/2012/12/04/midi-jitter 16

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) 17

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 https: //blog. etcconnect. com/2017/03/midi-show-control-midi-note/ 18

Advantages/Disadvantages Advantages: ● 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 19

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 20

Further reading ● The MIDI 1. 0 Specification: https: //www. midi. org/specificationsold/category/midi-1 -0 -detailed-specifications ○ Requires a free account to download ● Summary of MIDI Messages: https: //www. midi. org/specificationsold/item/table-1 -summary-of-midi-message 21

Questions ? 22