School of Informatics CG087 Time-based Multimedia Assets MIDIDr Paul Vickers1 MIDI Introduction to the Musical Instrument Digital Interface

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers2 Happy birthday! Well, it’s 20 years old this year Sigh. And I can remember the feature on Tomorrow’s World when I first heard about it… Vince Clarke (Depeche Mode, Yazoo, Erasure) used to have 8 Casio CZ-101s and 1 BBC Model B Microcomputer connected by UMI-2B MIDI audio stolen from Mad Jack’s page

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers3 Myself? I had a BBC B and an Acorn Music 500 synth It had no keyboard and was programmed using its own programming language Ample Music on this page stolen from Colin Fraser’s 500 page

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers4 Today? Roland D-20 (1990) Boss DS-330 (1993) Oberheim MC-3000 (2000)

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers5 So what is it? It’s a communications protocol A music description language in binary form. Each word describing an action of musical performance is assigned a specific binary code. MIDI was designed for keyboards, so many of the actions are percussion oriented. To sound a note in MIDI language you send a "Note On" message, and then assign that note a "velocity", which determines how loud it plays. Other MIDI messages include selecting which instrument to play, mixing and panning sounds, and controlling various aspects of electronic musical instruments.

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers6 History Early synths (1970s) were not designed with interconnectivity in mind. Connected via two control ports, one for pitch and note on/off events, and the other to provide a timing reference. –The first consisted of two signals: a variable DC control voltage (CV), proportional to pitch; and a trigger pulse, or gate. –The second port consisted of a pulse train synchronized with an external clock

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers7 Drawbacks of CV Only one note at a time could be controlled –Newer polyphonic instruments suffered No agreement over external clock rate –Special conversion boxes were needed to over- or under-sample the clock –Connecting multiple instruments, especially from different manufacturers was complex and troublesome

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers8 Advent of MIDI In 1983 Sequential Circuits, Roland Corporation, and Oberheim Electronics released MIDI 1.0 MIDI spec. controlled by –MIDI Manufacturer's Association (MMA)MIDI Manufacturer's Association –Japan MIDI Standards Committee

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers9 The specification MIDI specifies –Hardware interface –Binary control language –MIDI file format

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers10 MIDI hardware Bi-directional serial asynchronous link with data rate of 31,250 bits per second –320  s to transmit 10 bits (MIDI byte is 8 data bits plus a start bit and a stop bit = 10 bits) –In 1s can transmit >3000 bytes Requires a 5-pin 180  DIN connector –Pins 1 & 3 not used –Pins 4 & 5 carry 5mA current loop –+5v = binary 0, 0v = binary 1 Ports have opto-isolation to prevent interference

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers11 Electrical specification Data converted by UART ( universal asynchronous receiver transmitter ) UART and microprocessor communicate via interrupts and buffers

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers12 Port requirements A MIDI device must have –MIDI-IN and MIDI-OUT –Optionally MIDI-THRU Thru port transmits a copy of data received on the IN port

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers13 Connections 1 - synth to computer From

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers14 Connections 2 - more complex Daisy chain links shouldn’t exceed 3 devices due to transmission delays

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers15 Connections 3 – star network

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers16 MIDI bytes Two types of information –Status –Data Status messages generally indicate actions (e.g. pressing a key on the synth) Data bytes supply the information for the status byte (e.g. velocity of key press)

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers17 MIDI message A MIDI message has one status byte followed by 0..n data bytes Status and data bytes are differentiated by bit 7 Thus MIDI values go from (2 7 )

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers18 Channels If > 1 device connected, which one should respond to the messages? Messages are assigned to channels (16) Devices set to respond to particular channels Every message (except system messages) have a channel number which is stored in bits 0..3 of the status byte

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers19 7 status messages 000 – Note off 001 – Note on 010 – Polyphonic key pressure 011 – Control change 100 – Program change 101 – Channel pressure (aftertouch) 110 – Pitch bend Note on for channel 3 =

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers20 Example message Note on uses 3 bytes –Status byte –Data byte for note number –Data byte for velocity So, middle C (midi note no. 60) at medium volume (velocity 64) on channel 3 would be: – (note on, channel 3) – (data byte, value 60) – (data byte, value 64)

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers21 Other messages Other messages allow you –to select another timbre on the synthesiser (program change) –Add pitch bend –Add sustain –Change volume –Etc.

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers22 Not a sound format As it’s only a control language, it’s not a sound format MIDI merely allows devices to speak the same language A MIDI file is a sequence of note-on note-off messages to instruct a tone generator to play music The sound quality is totally depended on the quality of the synthesiser playing the file

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers23 MIDI files Standard MIDI files (SMF) is a specification for storing MIDI data 3 types: 0, 1, and 2 which just differ in the way the data are stored MIDI files can be played by Windows Media Player (and others) and can be loaded and edited by MIDI sequencing software (word processors for MIDI!), e.g. Digital Orchestrator Pro MIDI files don’t contain sound

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers24 Input & control MIDI input normally comes from a MIDI-equipped instrument –Synthesiser/digital piano, etc. –Guitar with MIDI converter –Wind instrument converters (yes) –CV-MIDI boxes for old synths –Even voice-MIDI converters Or from MIDI files Or you create MIDI data using special sequencer programs

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers25 MIDI sequencing Sequencers originally were hardware devices that allowed you to store sequences of control voltages to control CV synthesisers Sequences were normally notes, but could be filter settings, gate controls, etc Then MIDI hardware sequencers were developed At the same time, people wrote software sequencers for Atari ST, Sinclair Spectrum, BBC Micro, Commodore Amiga

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers26 MIDI sequencers Cubase and Cakewalk are the two most well- known and long serving programs Professional studios now use –ProTools ( –Cubase ( –Logic ( –Reason (

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers27 Sequencers A sequencer –Allows you to compose and store sequences of MIDI data to create songs –Organises the data in tracks (like on a multi-track tape recorder) –Has rich editing facilities (like a word processor) –Often prints music scores too Current sequencers now let you mix audio with the MIDI data (see next week)

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers28 Limitations of MIDI Not sufficient for music scoring Assumes a 12-tone chromatic framework –What about just intonation? –Micro tuning? –Enharmonic distinctions (e.g. F sharp vs. G flat) No way to represent performance dynamics –E.g. crescendo, diminuendo, etc. Slow serial ports 16 channel limit

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers29 Things to do with MIDI Control one synth from another Write and store music (sequencing) Write your own MIDI programs Sonify your own web pages (really!) –See Combine MIDI with audio Control effects boxes and light shows –Yes, you can do this. My reverb unit accepts MIDI controls so my synth can turn on the unit’s echo

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers30 Web sites (MIDI manufacturers’ association) Do some programming in CSound –Boulanger, R., Ed. (2000). The CSound Book: Perspectives in Software Synthesis, Sound Design, Signal Processing, and Programming. London: The MIT Press

CG087 Time-based Multimedia Assets School of Informatics MIDIDr Paul Vickers31 More reading Braut, C. (1994). The Musician's Guide to MIDI Sybex. ISBN Roads, C., Ed. (1998). The Computer Music Tutorial. Cambridge, Massachusetts: MIT Press. ISBN Kientzle, T. (1997). A Programmer's Guide to Sound. Reading, Massachusetts: Addison-Wesley. ISBN Selfridge-Field, E., Ed. (1997). Beyond MIDI: The Handbook of Musical Codes. Cambridge, Massachusetts: MIT Press. ISBN