MIDI Glossary

Active sensing : Not many MIDI devices seem to implement this feature. The basic idea is for a MIDI active sensing message to be periodically sent by the MIDI controller. If a broken cable or something of this nature results in a breakdown in communications, the controlled equipment will detect the absence of the active sensing messages, and will switch off all notes. Otherwise, any notes that are left switched on will remain so indefinitely.

Baud : This is the speed at which data is transmitted in a serial data system (such as MIDI). MIDI operates at 31250 baud (or 31.25 kilobaud), which means that with a continuous stream of data some 31250 bits of information per second are sent. This is not quite as good as it might at first appear, since ten bits (including timing bits) per byte are required, and typically three bytes per MIDI message are needed. This works out at around one thousand MIDI messages per second. This is adequate for most purposes, but with complex systems it is possible for MIDI to become overloaded.

Binary : A form of numbering system where the only digits used are 0 and 1. This may seem a bit crude, but it is the system used in all digital electronics, and MIDI sends values in the form of binary numbers.

Bit : Bit is an abbreviation for 'binary digit', which is the basic unit of information used in a digital system (such as MIDI).

Byte : Digital systems normally operate on 8 bits of data at a time, and a group of eight bits is a byte. Even with a system such as MIDI where data is sent one bit at a time, the bits are still grouped into 8 bit bytes.

Chain connection: See 'THRU'.

Channel : MIDI can operate on up to 16 channels that are normally simply called channels 1 to 16. Many MIDI messages carry a channel number, and can be selected by just one instrument (mode 3) or one voice of an instrument (mode 4). Note that any equipment set with 'omni on' will simply ignore channel numbers and respond to all messages.

Channel messages : These are simply the MIDI messages that carry a channel number in the header byte, and which can therefore be directed to one instrument, or one voice of an instrument. These messages include such things as note on, note off, and program change instructions. Messages that do not contain a channel number are called system messages.

Clock : A clock signal (in electronic music) is a regular series of electronic pulses sent from one sequencer to another in order to keep the two units properly synchronized (a system which is mainly associated with drum machines). In MIDI, the clock signal is a regular series of MIDI clock messages, rather than just a simple series of pulses.

Controller (1) : MIDI controller messages enable individual controls of an instrument or other piece of MIDI equipment to be adjusted. For example, they can be used to vary the parameters of an ADSR envelope shaper (variable controllers), or to permit the low frequency modulation to be switched on and off (switch controllers).

Controller (2) : A MIDI controller is also any device that transmits MIDI codes, and which can therefore control other MIDI equipment. Originally MIDI controllers were keyboards, but these days there are computer based controllers, foot pedals, guitar controllers, and various other types. You do not have to be a keyboard player in order to exploit the power of MIDI.

Copy protection : This is where a software producer uses some system of data encoding (or whatever) to prevent program disks and tapes from being copied. The idea is to prevent people from copying software bought by their friends rather than buying their own (legitimate) copy. Some disks are copyable, but the copies will not load and run properly. Another method, and one that is popular with the more expensive programs, is to have a 'dongle', or 'security key'. This is an electronic device which connects to one of the computer's ports. Dongled software can be copied, but will not run without the right dongle connected to the computer. The use of copy protection and similar methods by the software publishers is quite understandable. On the other hand, it can be inconvenient to users who are presumably paying any extra costs involved.

Delay : Some sequencers have a delay facility, which enables data for one track to be sent slightly delayed relative to data for another track. The idea of this is to permit instruments to be properly synchronized when one responds more rapidly to data than another. This is not an effect I have encountered, but a delay facility is presumably more than a little useful with a system that does suffer from this problem. Significant delays are sometimes introduced (so it is said) when data passes from an 'IN' socket to a 'THRU' socket. With a large system using the chain method of connection it is corrupted data rather than significant delays that would seem to be the main danger.

DIN connector : This is the standard type of plug/socket used for MIDI interconnections. Note that it is no good trying to buy just any DIN connector, as there are numerous types. The variety used for MIDI interconnections is the 5 way 180 degree type.

Disk : A computer disk is a device for magnetically storing data (sound samples, songs for a sequencer, etc.), and a disk drive is the hardware that records data on to and reads it back from a disk. Disks enable libraries of data to be built up, and provide a reasonably permanent form of storage (remember that the memories of many instruments and virtually all computers are completely lost when the power is switched off). Cassette recorders are often used as a cheap alternative to disk drives, but are slower and less convenient.

Event : A MIDI event is merely a MIDI message of some kind. Sequencers often have their storage capacity specified as a certain number of events. As note on and note off commands are separate events, and after-touch or other messages may be involved, the maximum note capacity is likely to be less than half the maximum number of events that can be accommodated.

Expander : A MIDI expander is an instrument that has no keyboard and can only be played via its MIDI IN socket and an external keyboard or other controller. Sounds are sometimes preset and non-adjustable, but some of the more recent units are quite versatile. Originally intended as add-ons for organs, the better expanders potentially have much wider application.

Filter : A MIDI filter is not an audio filter that is controlled by way of MIDI signals. It is a device that connects into the MIDI cable and blocks certain types of message from its output. For example, a filter could be added ahead of an instrument that has only omni modes and will respond to messages on all channels. By removing all channel messages except those on a particular channel, the instrument could effectively be used in mode 3.

Hard disk (fixed disk) : Normal computer disks are often called floppy disks, as the disk on which magnetic coating is deposited is far from rigid. A hard disk is a more sophisticated type where the disk is rigid, rotates continuously at high speed, and cannot be removed from the drive. The non - interchangeability of the disks is not a major drawback, as the capacity of a hard disk is typically equal to that of about 60 floppy disks. The point of a hard disk is that it gives very rapid access to vast amounts of data. An increasingly popular feature on up-market computers, and also to be found on some of the more recent sound samplers.

Hardware : Hardware is simply any piece of electronic equipment, including computers and musical instruments. Data or programs used by the equipment is the 'software'. Data or programs held on ROM are sometimes referred to as 'firmware', presumably because they are a combination of software (the data in the ROM) and hardware (the ROM itself)!

Hexadecimal (hex) : Hexadecimal is a system of numbering based on 16 (rather than ten like the ordinary decimal system). The normal numeric digits from 0 to 9 are augmented by the first six letters of the alphabet (A to F) in order to give the 16 different single digit numbers required by the system. Equipment manuals often give MIDI codes in hexadecimal form, but usually include a conversion table that gives hex to decimal conversions.

Icon : See 'WIMP'.

Kilobyte (k) : The storage capacity of computer disks and memory circuits is often quoted in kilobytes, or just as so many 'k'. A kilobyte is 1000 bytes of data, or, if you wish to be pedantic, 1024 bytes.

Librarian : This is a computer program that stores sets of voice data for synthesizers or other instruments. It enables the required sounds to be quickly selected and loaded from disk and transmitted to the instrument via MIDI. Megabyte The capacity of large memory circuits and high capacity disks is often quoted in megabytes. A megabyte is equivalent to 1024 k, or 1048576 bytes.

MIDI choke : A term used to describe what happens if a system is called upon to transmit more data than MIDI can handle. Exactly what happens when MIDI choke occurs depends on the system, but at the very least it is likely that the timing of note on/off messages will be severely disrupted. In an extreme case it is possible that the MIDI controller would crash, and the system would be brought to a halt. Mono In a MIDI context 'mono' means that only one note per channel is possible. In MIDI mode 2 an instrument is truly monophonic as operation on only one voice is possible, but in mode 4 (formerly known as mono mode) it is possible for an instrument to operate monophonically on several channels. The instrument is then polyphonic, while it is the MIDI channels that are monophonic. The term mono is perhaps a bit misleading in this respect.

Mouse : See 'WIMP'.

Notation program : Also called 'score writer' programs, these permit music to be written into the computer in standard music notation form. Some programs of this type are simply intended as a means of producing sheet music, but many now support MIDI, and will operate as step-time sequencers. In fact some will turn MIDI data into notes on the staves, and will operate as real-time sequencers (but will not necessarily work particularly well in this role).

Omni : When 'omni' is 'on', an instrument will respond to messages on any MIDI channel. When 'omni' is 'off', the instrument will only respond to one particular channel (mode 3), or each voice will be assigned to a particular channel (mode 4).

Pointer : In the sense of a song pointer, it is a MIDI message that moves a sequencer to a certain point in the sequence. As a computing term it means an on screen pointer (see 'WIMP').

Poly : In a polyphonic mode an instrument can handle several notes at once. In mode 3 it is possible to have polyphonic operation on each MIDI channel. The maximum number of notes available at one time is determined by the instrument,the MIDI specification does not set any upper limit.

Port : A port is merely some form of electrical connector on a computer or other piece of electronics to enable it to be connected to some peripheral device. MIDI IN, OUT, and THRU sockets are all examples of ports. The alternative term interface is sometimes used.

Printout : Some programs enable data to be printed via a suitable printer. This is very useful, especially with something like a sequencer program that permits only a small portion of long sequences to be displayed on the screen. Also useful with notation (score writer) programs where it enables conventional sheet music to be produced. However, for graphics output a graphics compatible printer is needed (most programs will work properly with any Epson compatible dot-matrix printer).

Program change : Most instruments and other items of MIDI equipment make use of 'programs'. In an instrument, for example, these are a series of preset control settings that give a range of different sounds. Program change messages therefore permit the required sounds to be selected at the appropriate times. Other items of MIDI equipment such as mixers and effects units are often controlled via program change messages.

Program dump : Many MIDI equipped instruments have the ability to send out via MIDI the full contents of their program memory, or to provide a 'program dump'. This can be used to send a set of programs from one in- strument to another (but they will normally need to be instruments of exactly the same type). This facility can also be used to send data to a computer or MIDI disk drive, and then feed it back again when and as required. There is no special MIDI program dump message, and this facility operates under system exclusive messages.

Qwerty keyboard : A term which seems to confuse a lot of people, it simply refers to a typewriter style keyboard (as used in expanded form on virtually all computers). 'Qwerty' is the first six letters on the top row of letters keys.

RAM : This is an acronym for random access memory. If you program an instrument (or a computer) this is the electronic circuit that is used to store the information. The contents of RAM are lost when the power is switched off, but many instruments have a battery to power the RAM after switch-off so that contents of the memory are retained. I have not encountered any computers with the ability to store more than very limited amounts of memory in this 'battery-backed' RAM.

Real-time sequencer : A sequencer where the music is entered into the unit simply by playing it on a MIDI keyboard. The sequencer records the data from the keyboard, which is stored in its memory together with timing information. The ability to change the playback speed is a standard feature. The more up-market systems permit note values and durations to be edited, and multi-track sequences to be built up.

ROM : ROM stands for read only memory. As this name suggests, once the contents of ROM have been set at the manufacturing stage they cannot be altered. The main point about ROM is that it retains its contents when the power is switched off (unlike ordinary RAM). ROM is used for storing data and (or) programs that will be needed frequently. RAM (see above) is what is needed for storing your own data and programs.

Serial : MIDI is a form of serial communications system, which simply means that it sends information one 'bit' at a time. Parallel systems send data several 'bits' at a time, and are usually much faster. They need multi- way connecting cables though, and often have very restricted ranges (a couple of metres in some cases). Although slower, a serial system is more practical for many applications.

Software : Software originally meant computer programs in any form (on disk, tape, written down, or whatever). It seems to be more generalized nowadays, and sound samples for use in a sound sampler would be considered 'software'.

Star connection : See 'THRU-box'.

Steptime sequencer : This is a sequencer where the music is programmed by specifying the note value and duration in some way other than playing the music on to a MIDI keyboard and recording the MIDI output data plus timing information. A notation program where the music is placed on to an on-screen stave (or staves) in conventional music notation form is an up-market example of a step-time sequencer. With more simple types the notes are entered in a more simple form, such as 'C-2, 1/4 note' for instance. Great if your imagination out-performs your playing skills, but a relatively slow way of doing things.

System exclusive : The system exclusive messages are ones that are designed for use only by equipment from one manufacturer. The header byte includes an identification number so that system exclusive messages from equipment of the wrong manufacturer can be filtered out and ignored. Virtually any feature can be implemented using system exclusive messages, and unlimited data can be included in each one of these!

System messages : These are the MIDI messages that do not carry a channel number in the header byte. They are therefore responded to by every piece of equipment in the system that recognizes them. These are mainly the MIDI clock and associated messages.

THRU : A THRU socket is to be found on many items of MIDI equipment. It simply provides a replica of what is received on the IN socket. In a multi-unit system the THRU socket on one unit can be coupled through to the IN socket of the next unit (chain connection).

THRU-box : Not all MIDI units have THRU sockets, and in particular, they are often absent from keyboard instruments. A THRU-box has a MIDI IN socket and several THRU output sockets. In a multi-unit system the OUT socket of the controller connects to the IN socket of the THRU-box. The THRU outputs then connect to the IN sockets of each instrument etc. in the system (star connection).

Voice editor : The minimalist approach to synthesizer controls has made setting up the required sounds a relatively long and difficult process. A voice editor program provides on-screen controls that can quickly and easily be adjusted. New control settings are almost instantly sent to the instrument via MIDI so that the effect of adjusting controls can be heard, and fine adjustments easily made.

Visual editor : A program for use with sound samplers, it draws out waveforms on the screen so that suitable start, end and loop points can be selected quickly and accurately. Relies on swapping sound sample information via MIDI system exclusive messages.

WIMP : WIMP is an acronym for Windows, Icons, Mouse, and Pointer. [Not to be confused with the term in physics which means Weakly Interracting Massive Particles] It is a means of controlling computer programs, where an on screen pointer is moved around the screen using a hand operated controller (the mouse). The mouse and pointer are used to select options via icons, which are on-screen graphical representations (pictures of various instruments so you can select the one you wish to use for example). The windows are areas of the screen which are given over to different functions, or with some computers can even be used for different programs! A WIMP environment makes it easy for inexperienced users to operate complex programs, but only if the software is well designed and the computer is powerful enough to run it properly.

Window : See 'WIMP'.

Word : In a computer sense, this is a group of bits that is longer than a normal 8 bit byte. For example, with a 16 bit sound sampler, a memory capacity of 500 k words means that 500 k of full 16 bit words can be accommodated (which is equivalent to 1000 k bytes of storage).

XLR : This is a type of electrical connector used for MIDI interconnections on some equipment (generally units that are designed for rough handling on the road). Any supplier of MIDI equipment which uses this type of connector should be able to supply suitable connecting leads as well, together with adaptors to permit standard 5 way DIN MIDI leads to be used.





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Practical MIDI Handbook File Info: Created 15/7/2000 Updated 8/7/2004 Page Address: http://www.fortunecity.com/templarseries/midiglos.html