Introduction to MIDI

1. Introduction to MIDI Musical Instrument Digital Interface (Thanks to Bob Lang)

2. MIDI Overview • Developed in mid 1980s by a consortium of synthesizer manufacturers. • Now fitted to budget equipment. • Initially used point-to-point serial lines (current loop) with 5 pin DIN plugs. • Sends commands, not note samples. • Serial lines being phased out and replaced by the faster USB.

3. MIDI Data Flows • The original serial line system only allowed for point-to-point connections and data flow in ONE direction. • There are three possible connection ports on a MIDI device: • Out - for transmitting data to another device. • In - for receiving data from another device. • Thru - re-transmits data received at the In port. • The Thru port allows several devices to be connected into a network.

4. Typical Studio Setup Data flow USB/MIDI Interface In Thru Out In Data flow MIDI Controller Keyboard Out Rack mounted synthesizers (each set to a different channel)

5. MIDI Channels • In a traditional setup, each instrument receives the commands for every other instrument on the network. Therefore, it must ignore commands for other instruments. • This is achieved using channels: • Each command holds a channel number (1-16). • Simple (single voice) instruments are set up to respond to commands on one fixed channel. • Multi-timbral instruments are often set up to respond to commands on more than one channel, with each channel number controlling a different voice.

6. Typical Home Setup USB/MIDI Interface • Multi-timbral Home Keyboard: • responds on all channels • each channel has a different voice Out In

7. Channels and Voices • Each channel corresponds to a different voice: 1: piano; 2: bass; 10: drums • The precise voicing for each channel is specified by a Program Change command. • As defined, a Program Change can only choose between 128 different voices. • However, a Bank Select command can also be used. This supports128 different voice banks, each with 128 different voices (=16,384 voices) Note: Voice = Patch = Program Bank = Collection of 128 different voices

8. Playing Notes • A MIDI instrument starts playing a note when it receives a Note On command for a channel that it is currently monitoring. • The Note On command specifies which note to play and how loud to play it. • The instrument stops playing the note when it receives a Note Off command for that note.

9. Playing Chords • Most modern instruments can play chords. • Each note in the chord must be triggered by an individual Note On command. • Each note in the chord must be turned off by an individual Note Off command.

10. Note On Command • A Note On command contains the following data: • The channel number (1-16) • The pitch of the note (see next slide) • The velocity (loudness) of the note (1-127) • The command requires just 3 bytes. • The note plays until stopped by a Note Off. • The note sounds using the currently selected voice for the channel number.

11. Note Pitch 36 38 40 41 43 45 47 48 50 52 53 55 57 59 60 62 64 65 67 69 71 72 74 76 77 79 81 83 • In MIDI, the pitch of a note is specified by a number: • Middle C = 60. • Add or subtract 12 for each octave up or down. • Add or subtract 1 for each semitone up or down. • Total range 1-127 or around 10 octaves!

12. Drum Sounds and Pitch 36 38 40 41 43 45 47 48 50 52 53 55 57 59 60 62 64 65 67 69 71 72 74 76 77 79 81 83 • Most drum sounds do not have a pitch. • Many drum sounds can be put into a single patch. • Pitch number selects the required drum sound. Hand Clap Hi Hat Ride Cymbal Vibra slap Open Conga Short Guiro Bass Drum Low Tom Hi Mid Tom Splash Cymbal Hi Bongo Hi Agogo Open Cuica

13. Note Off Command • A Note Off command turns off a note that is playing. It has the following data: • The channel number and note pitch • The “Release Velocity” • As with Note On, it only requires 3 bytes. • Release Velocity specifies how quickly the note should die away (but is usually ignored on cheap equipment). • An alternative form of Note Off is to send a Note On with a velocity (loudness) of zero.

14. Control Change Command • An instrument may support some “controls”. • Set up using a Control Change command. • Each command works on a single channel. • Typical controls are: • Bank Select - select voice bank for this channel. • Pan - stereo placement between Left and Right. • Volume - overall volume level. • Expression - varying volume level. • Sustain - how the note sound dies away. • Chorus - a special effect.

15. General MIDI (or GM) • General MIDI was devised to allow easy swapping of MIDI files and sequences. • Instruments marked with the GM logo must conform to a minimum specification: • A bank of 128 named voices with fixed numbers. • Channel 10 reserved for drums and percussion. • A minimum set of controls, including volume, pan, expression and sustain. • Manufacturers such as Yamaha and Roland have brought in their own extensions to GM to lock in users to their platforms.

16. Newer Studio Setup (USB) Note: MIDI commands sent via USB USB Hub Other USB devices USB USB Controller Keyboard USB USB Multi-timbral Tone generators

17. USB and MIDI • MIDI originally used a relatively slow serial transmission system. • Increasingly, instruments are implemented with USB replacing the slow serial ports. • USB is faster, more flexible and supported by all modern computers. • Multiple tone generators (each with 16 channels) can be individually addressed. • The MIDI commands are the same in all cases.