Digital Audio IV MIDI Overview

Sending MIDI Information I. Serial Transmission A. Single cable to move data B. Slower than parallel, but is less expensive and allows for longer cable runs II. MIDI uses a DIN connection A. Standard 5 pin DIN connector B. Simple, readily available, inexpensive, already used in many audio and video applications

MIDI PLUG Pins 1 & 3:Not Used Pin 2:Shield Pin 4:Ground Pin 5:Data

MIDI In/ Out/ Thru  Midi In receives MIDI information from another device.  MIDI Out sends MIDI data produced by the device out to another midi device.  Midi Thru passes on any MIDI messages received by the MIDI in port. Anything played on a MIDI instrument goes to the MIDI out port, not the MIDI thru port.

The Basics  All MIDI instruments and devices use 8 bit processors.  Can process values from  MIDI messages are grouped in clusters called packets.  Packets consist of Status and Data Bytes

Status Bytes  Describe the kind of information being sent  Always the first code number sent by a MIDI instrument  Channel information is included in status bytes  Status - values from

MIDI Channels  Four of the eight bits of a status message specify the MIDI Channel. 4 bits have 16 possible values (2 n where n is the # of bits), so MIDI has 16 channels available.  MIDI channels make it possible for each instrument in a system to play a unique part while connected together by a single MIDI chain.

Data Bytes  Values of actual MIDI events  Follows status bytes  Data - values from 0-127

5 Types of MIDI Messages  Channel Voice Messages  Channel Mode Messages  System Common Messages  System Real Time Messages  System Exclusive Messages

Channel Voice Messages  Note on/ off  Polyphonic Aftertouch  Control Change  Program Change  Channel Pressure  Pitch Bend Change

Channel Mode Messages  All Sound Off  Reset All Controllers  Local Control On/ Off  All Notes Off  Omni Mode Off/ On  Mono Mode On  Poly Mode On

System Common Messages  MTC (MIDI Time Code)  Song Position Pointer  Song Select  Tune Request  End of Exclusive Message

System Real Time Messages  Timing Clock (MIDI Beat Clock)  Start - Continue - Stop  Active Sensing  System Reset  Undefined

 Synchronization depends on two factors:  Clock reference or speed (i.e. How fast are we going?)  Positional reference (i.e. Where are we?) MIDI Synchronization

 MIDI Beat Clock  Sequencers and drum machines have built-in timing clocks that let you set them to a desired tempo.  Real time messages are sent out in time with the music - the faster the tempo, the faster the messages are sent (24 Pulses Per Quarter note or PPQ). Clock Reference

 MIDI Time Code (MTC)  Provides location information (i.e. Where are we?)  Location is broken down into 4 sets of numbers:  Hours: Minutes: Seconds: Frames Common Frame Rates/Applications  30 Frames Per Second (FPS) – Audio Only  FPS – Color Video (NTSC standard used in USA)  24 FPS – Film  25 FPS (EBU/PAL standard used in European countries) Positional Reference

SMPTE and MTC

System Exclusive Messages (Sys Ex)  The memory inside a MIDI instrument stores info about the patches as a list of parameters.  These parameters are unique to each instrument and include info on waveforms, brightness, and other timbral elements.  System Exclusive messages allows this info to be sent between similar instruments and from instruments to computers or sequencers.

Recommended Practices The first specification (1983) did not define every possible "word" that can be spoken in MIDI, nor did it define every musical instruction that might be desired in an electronic performance. So over the past 20 or more years, companies have enhanced the original MIDI specification by defining additional performance control messages, and creating companion specifications which include:  MIDI Machine Control  MIDI Show Control  General MIDI  Downloadable Sounds  Standard MIDI Files (SMFs)

MIDI Machine Control MMC  MIDI performs other non-musical tasks that have special System Exclusive Codes called MIDI Machine Control.  These codes can operate video and audio recording decks or automate lighting rigs and other functions that require precise timing.

Standard MIDI Files MIDI Files may be of two types:  Type 0 – All MIDI parts are condensed onto a single MIDI track.  Type 1 – All MIDI parts kept on separate tracks.  MIDI files have a (.MID) extension on both PCs and Macs

Standard MIDI Files Setup Data  An SMF also should have data (commonly referred to as a ‘header') that contains:  Tempo  Instrument selections per Channel  Controller settings  Copyright notices  Composer