Music Technology I TEDT1245 Semester 1 What is MIDI? MIDI stands for Musical Instrument Digital Interface and it a common language communications protocol that allows any MIDI-equipped electronic musical instruments to interact with each other. MIDI is a means of transmitting instructions or messages NOT a means of transmitting audio. MIDI allows computers, synthesizers, MIDI controllers, sound cards, samplers and drum machines to control one another, and to exchange system data. How does MIDI work? MIDI does not transmit an audio signal or media — it transmits "event messages" such as the pitch and intensity of musical notes to play, control signals for parameters such as volume, vibrato and panning, cues, and clock signals to set the tempo. As an electronic protocol, it is notable for its widespread adoption throughout the industry. All MIDI compatible controllers, musical instruments, and MIDI-compatible software follow the same MIDI 1.0 specification, and thus interpret any given MIDI message the same way, and so can communicate with and understand each other. MIDI composition and arrangement takes advantage of MIDI 1.0 and General MIDI (GM) technology to allow musical data files to be shared among many different files due to some incompatibility with various electronic instruments by using a standard, portable set of commands and parameters. Because the music is simply data rather than recorded audio waveforms, the data size of the files is quite small by comparison. The MIDI interface: MIDI compatible instruments and other MIDI devices are connected together using standard MIDI cables, which have a male 5-pin DIN connector at each end. Pin 1 & 3 - are not used Pin 3 - used as shielding. The cable screen is connected to this pin. Pin 4 - is a 5-volt current loop to ensure that electricity flows in the correct direction. Pin 5 - used to transmit the MIDI data. A drawing of a MIDI connector from the cable end: The MIDI data is sent down the cable one bit at a time as a stream of information, which is called a serial interface. A parallel interface allows information to be sent down separate wires so that the message reaches the device at the same time, making it faster than a serial interface. The speed of a MIDI serial interface is 31,250 bits per second. There are 8 bits needed for every MIDI word plus 2 bits to mark the gaps between words, therefore there can be up to 3,125 messages per second. The MIDI Language The MIDI language is represented with binary code. Each 0 or 1 is called a bit. Four bits equal a nibble and eight bits equal a byte. With MIDI, each digital word consists of a total of 8 bits (or 1 byte). An 8 bit number system can only count from 0 to 255. Therefore MIDI bytes are divided into 2 distinct types: Status Byte – describes the type of information being sent. They tell the receiving device weather the message is a not on, note off, pitch wheel or any other action. Data Byte – follow status bytes and indicate actual values of the Status Bytes. If a Status Byte is sent indicating a note on action, the following Data Bytes will represent the note number and the note velocity. The difference between Status Bytes and Data Bytes is indicated by the value of the Most Significant Bit (MSB), which is the bit on the furthest left of the message. A byte is a Status Byte if the most significant bit is set. This means that the left most bit of the byte (eight zeros or ones) is a 1. 1bbb bbbb (b = 0 or 1) eg 1 0 1 1 0 1 1 0 A byte is a Data Byte if the most significant bit is not set. This means that the left most bit of the byte (eight zeros or ones) is a 0. 0bbb bbbb (b = 0 or 1) eg 0 1 1 0 0 0 1 1 MIDI Channels The lower 4 bits of a Status Byte are used to specify the MIDI Channel. 4 bits have 16 possible values (0 to 15) and so MIDI has 16 channels. Binary MIDI CHANNEL Binary MIDI CHANNEL 0000 Channel 1 1000 Channel 9 0001 Channel 2 1001 Channel 10 0010 Channel 3 1010 Channel 11 0011 Channel 4 1011 Channel 12 0100 Channel 5 1100 Channel 13 0101 Channel 6 1101 Channel 14 0110 Channel 7 1110 Channel 15 0111 Channel 8 1111 Channel 16 Therefore a Status Byte 1xxx 0010 is on MIDI Channel 3 Status Bit MIDI Channel The xxx are used to indicate what the status of the message is going to be. Eg: a note on A note off Program change Visit this website to view a complete list of MIDI messages explained including their Binary code, Hexadecimal and Decimal values. This will give a clear understanding of MIDI messages and what they look like: http://www.midi.org/techspecs/midimessages.php Data Bytes The 7 numbers that follow the Most Significant Bit of a Data Byte are what are used to carry the data value. These represent a series of values or steps that count from 0 to 127. Remember: a MSB value of 0 indicates a Data byte. The smallest number possible is 00000000 = 0 The biggest number possible is 01111111 = 127 Thus the possible range of values a Data byte can be is 0-127. This explains why many MIDI controllers, such as volume or velocity, have a maximum value of 127. A breakdown of the Data Byte message is as follows: MSB 64 32 16 8 4 2 1 (value of each bit) 0 1 1 1 1 1 1 1 (0111 1111 – Data Byte) (128) 64 + 32 + 16 + 8 + 4 + 2 + 1 = 127 (total value) MIDI message example Here is an example of a simple 3-byte MIDI message comprising a Status Byte and 2 Data Bytes. This message is telling a sound module set to respond on MIDI channel 1 to start playing a note (C3) at a velocity of 101. What makes up the MIDI Language? Electronic keyboard instruments are, by definition electronic, which means the sound is created by electronic circuitry – not the instrument itself. When a key on an electronic MIDI instrument is pressed down, a digital signal – a note on is transmitted. When that note is released, a note off message is sent. The actual note or key number depends on the note or key that is pressed. How hard the key is pressed generates the loudness or velocity of the note. MIDI is not a means of transmitting audio, but a means of transmitting instructions. MIDI MESSAGE EXERCISE Define the following Binary Codes: Eg 1001 0001 = Status Byte / Decimal = 145 1001 0011 = Status Byte / Decimal = 147 0110 0101 = Data Byte / Decimal = 101 Now try these: 0101 0101 = ________Byte / Decimal = _______ 1011 1101 = ________Byte / Decimal = _______ 0110 1001 = ________Byte / Decimal = _______ 0001 0010 = ________Byte / Decimal = _______ 0111 1110 = ________Byte / Decimal = _______ 1111 0001 = ________Byte / Decimal = _______ MIDI Connections There are many types of MIDI connections. The MIDI Out sends digital messages out. The MIDI In receives MIDI information from another MIDI device. The MIDI Thru passes on a copy of MIDI messages from the MIDI In. The MIDI Thru port allows MIDI information to be passed on through to a series of sound modules all connected using the MIDI In and MIDI Thru ports. This provides the advantage of being very simple to set up, only requiring MIDI cables and nothing else. However, if any one cable is damaged or disconnected any sound module further down the line will not receive the information. It is possible to use MIDI Thru box to make copies of the signal. MIDI Echo Most MIDI sequencers and MIDI control software will have a MIDI Echo option. This allows MIDI In information and MIDI Out information to be merged together and be presented at the MIDI Out. Normally MIDI data arriving at the "MIDI in" port of some device is passed on to a through (thru) port of that device if one is available. This allows many devices to share a common MIDI bus. Only MIDI data created within that device is sent out of its MIDI out port. However, when MIDI Echo is enabled data arriving at the MIDI input is "echoed" back out of the MIDI output in addition to the thru port. This data may or may not be merged with other data generated by the device. MIDI Connections Example A Both keyboards have MIDI connections. Synthesiser A is the Master Keyboard and Synthesiser B is the MID slave device. Which connections would you use so that Synthesiser A is sending MIDI data to Synthesiser B? Example B All three keyboards have MIDI connections. Synth A is the Master and Synths B and C are the MIDI Slave devices. Which connections would you use so that Synth A is sending MIDI data to Synths B and C? Example C In this example we have added a computer and MIDI interface. The requirement is to connect the master keyboard to the computer so they can communicate with each other. Example D A multi-port interface receives MIDI data at the MIDI In ports and then copies the information and sends it out two or more Thru ports. Each MIDI port may be assigned to specific Thru ports. Again, try connecting the keyboard controller so that it sends information to the MIDI interface. Connectors: Keep in mind MIDI serial data is only via MIDI cables - Modern day MIDI devices now come with USB connectors, which allow parallel data transfer.