MIDI

1. MIDI • One choice for adding sounds to multimedia applications is the use of digital audio soundfiles • This can become very memory intensive, however, for large soundfiles • For example, a stereo 16 bit/sample 22 kHz soundfile requires > 5 mbytes per minute of audio • As an alternative to the use of soundfiles, MIDI files have been considered

2. MIDI • MIDI (Musical Instrument Digital Interface) is a standardized control language and hardware specification • allows suitably equipped electronic musical instruments and devices to communicate real-time and nonreal-time performance and control data • MIDI data is communicated digitally through a production system as a string of MIDI messages

3. MIDI • The messages are transmitted (in a serial fashion) through a single MIDI line at 31.25 K bits/second • Usually, MIDI instruments and devices are linked together in a daisy-chain fashion • The following slide shows an example

5. MIDI • MIDI messages are bytes that are interpreted by the MIDI devices • The messages are used to convey a series of instructions to one or all of the MIDI devices within the system. • The messages can be divided into two types: • Channel messages are messages assigned to a specific MIDI channel • System messages address all devices in a system, without regard to channel assignment

6. MIDI Messages • The following is a typical 3 byte MIDI Note On message: (10010101) (01000000) (01011010) • This message is interpreted as follows. • The first byte is the status byte while the second and third are data bytes • The most significant bit of the byte determines which type of byte it is • The next three bits of the status byte code the Note On message • The four least significant bits give the channel to which this message is directed • In the case, channel #5. (Note that we can have up to 16 channels addressed through a single MIDI cable)

7. MIDI

8. MIDI Channel Messages • Whenever a MIDI device is instructed to respond to a specific channel number, it will ignore any message not directed to that channel • On the other hand, if a message is transmitted to that channel, the device will respond to the message (within the device’s capability limits). • The 7 bits (not including the MSB) of the first data byte code the note # that should be turned on - here, it is 64 • The 7 bits of the second data byte indicate the attack velocity (volume level of the note) - here, it is 90

9. MIDI Channel Voice Messages • Channel voice messages are used to transmit real-time performance data throughout a connected MIDI system • There are seven channel voice messages: • Note On • Note Off • Polyphonic Key Pressure • Channel Pressure • Program Change • Control Change • Pitch Bend Change

10. MIDI Channel Voice Messages • A Note On message indicates the beginnning of a MIDI note • The message consists of three bytes of information: MIDI channel number; MIDI note number; Attack velocity value • In general, MIDI note 60 is assigned to middle C key, and notes 21-108 correspond to the 88 keys of an extended keyboard controller • The final byte indicates the velocity at which the key was pressed • Higher velocities lead to louder notes • Not all instruments interpret all attack velocities, and some do not respond dynamically at all

11. MIDI Channel Voice Messages • A Note Off message indicates the end of a MIDI note • If the instrument being played has a release (or decay) phase, it will begin that phase when the message is received • The release velocity byte indicates the speed at which the key was released • Few instruments generate or respond to release velocity

12. MIDI Channel Voice Messages • Polyphonic Key Pressure messages are transmitted by instruments that are capable of playing more than one sound at a time (e.g. a chord on a keyboard instrument) • The message indicates a pressure message for each key that is depressed • Pressure values can commonly be assigned to such parameters as vibrato, loudness, and pitch • Channel Pressure messages are commonly transmitted by polyphonic instruments that will only respond to a single overall pressure applied to their controllers, regardless of the number of keys being played at any one time

13. MIDI Channel Voice Messages • The Program Change message changes the program or preset number that is active in a device or instrument • Up to 128 presets can be selected by using this message • This can be used, for example, to switch between the different sounds of a synthesizer or to change the rhythm patterns of a drum machine

14. MIDI Channel Voice Messages • The Control Change message transmits information that relates to real-time control over the performance parameters of a MIDI instrument • Control change messages correspond to changes in controllers such as foot pedals, relative balance of a stereo sound field, etc. • Pitch Bend Change messages are transmitted by an instrument whenever its pitch bend wheel is moved either in the positive (raise pitch) or negative (lower pitch) position from its central (no pitch bend) point

15. MIDI Channel Mode Messages • Controller numbers 121-127 are reserved for Channel Mode messages. These include: • Reset all controllers • Local control • All Notes Off • MIDI Mode messages

16. General MIDI • The basic instrument sounds that are reproduced by almost any electronic music setup will invariably change from one setup to the next • This lack of conformity has brought about a single set of standardized MIDI patch settings that have come to be known as General MIDI • This standardized series of sound settings has been defined so that common and popular instrument sounds are mapped to various program change numbers

17. General MIDI Program # Instrument Group 1-8 Piano 9-16 Chromatic Percussion 17-24 Organ 25-32 Guitar 33-40 Bass 41-48 Strings 49-56 Ensemble 57-64 Brass 65-72 Reed

18. General MIDI Program # Instrument Group 73-80 Pipe 81-88 Synth Lead 89-96 Synth Pad 97-104 Synth Effects 105-112 Ethnic 113-120 Percussive 121-128 Sound Effects