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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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