introduction to midi in electronic dance music
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Technology can be considered one of mankind’s greatest assets, but ever so often a
user overlooks the intricacies that allows for ease of use. One such intricacy is MIDI,
which has aided many musicians in composing electronic music. Where a traditional
composer needs to have an intimate knowledge of music theory, MIDI has allowed a
musician with a basic understanding to be able to compose music. MIDI’s simplicity
has allowed for a new form of music composition to blossom where a person with
limited resources can produce music in their own ‘Home Studio’.
“Musical Instrument Digital Interface (MIDI) is a digital communications language and
compatible specification that allows multiple hardware and software electronic
instruments, performance controllers, computers, and other related devices to
communicate with each other over a connected network.” (Huber, 2007, p1)
MIDI transmissions or files do not contain any audio or sounds, but instead contain a
data stream, or ‘MIDI message’, which is traditionally used to manipulate parameters
in an external or internal sound module. A sound module, or sound generator, has
the capabilities to create an analog or digital signal, or sound, which can be
manipulated via an external MIDI controller, resulting in audial changes such as a
pitch change of a sound, the amplitude of a sound or how long a sound plays for.
The result from the sound module is an analog or digital signal which can then be
amplified through a speaker system for the sound to be heard by the user (Fig. 1).
Figure 1. MIDI Data And Audio Signal
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A MIDI message is made up of 8-bit bytes. A bit is a Binary unit, being either 0 or 1.
There are 8 bits in a byte and half of a byte, or 4 bits, is called a "nibble" or “nybble”
(Fig. 2).
Figure 2. Bit And 8-Bit Byte
A MIDI message usually consists of 3 bytes, the first being the Status, or header,
byte, followed by the Data byte(s). The very first bit of each 8-bit byte is called the
Most Significant Bit (MSB) and it determines whether a MIDI message is a Status
byte or a Data byte, which is 1 or 0 respectively (Fig. 3). The Status byte, or Most
Significant Byte (MSB), indicates which “function is to be performed by a device or
program”; and the Data byte, or Least Significant Byte (LSB), which follows after
Status byte, is to “associate a value to the event that’s given by the accompanying
status byte”. (Huber, 2007, p16)
Figure 3. A MIDI Message
As there are 7 bits, there are a total of 128 value variations possible when counting
in Binary code, which is calculated as 27. Although the number of variations of 7 bits
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is 128, computers and MIDI ‘recognise’ this maximum number as 127 as they start
counting from 0 (Fig. 4).
Figure 4. Status And Data Byte Binary Counting
The 3 bits in the Most Significant Nibble Status byte, after the header bit, are called
Channel Voice Messages and consists of Note-Off, Note-On, Aftertouch, Continuous
Controller, Patch Change, Channel Pressure, Pitch Bend Change or System
command bytes (Fig. 5). (Stanford University, 2012)
Figure 5. MIDI Channel Voices
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No.1 to 7 of Channel Voice Messages in (Fig. 5) is “used to transmit real-time
performance data throughout a connected MIDI system. They’re generated
whenever a MIDI instrument’s controller is played, selected, or varied by the
performer. Examples of such control changes could be the playing of a keyboard,
pressing of program selection buttons, or movement of modulation or pitch wheels.”
(Huber, 2007, p22)
The nibble that is after the 3-bit Channel Voice Messages is allocated for the MIDI
Channel number, which is often written as “Ch##” where “##” is the MIDI Channel
number. As there are 4 bits allocated to the MIDI Channel number, there are 16
variations possible, calculated as 24. (Fig. 6)
Figure 6. MIDI Channel Numbers
The MIDI Channel numbers give the user more flexibility in where a MIDI message is
sent to. A musician can connect multiple sound modules to one MIDI controller; and
by changing the MIDI Channel number in a MIDI message, they can direct the MIDI
transmission to the device of choice which would be using the same channel
number.
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Note-On and Note-Off messages (Fig. 7), Channel Voices 1 and 0, which contain the
MIDI channel number in the status byte, have two data-bytes that contain the values
for the MIDI Pitch Number and Velocity respectively, with the velocity being how fast
a key is pressed for Note-On and how fast a key is released for Note-Off. While this
is usually for playing a musically related note, it can also be used for triggering
events in a DAW (Digital Audio Workstation), in which it functions like a binary
switch, the Note-On Message, in binary terms, being 1 or ‘On’ and Note-Off being 0
or ‘Off’.
Figure 7. Note-On / Note-Off Voice Message
Aftertouch comes in two different forms; one which contains two Data bytes, the
Polyphony Key Pressure Voice message, and the one with one data byte, the
Channel Pressure Voice message. When a key has been depressed, there can be
further parametric changes, which can be done via exerting further fluctuating
pressure onto the depressed keys. Polyphonic Key Pressure allows each individual
key to have its own Aftertouch value, whereas Channel Pressure will only have a
“single, overall pressure, regardless of the number of keys that are being played at
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one time” (Huber, 2007, p25). Aftertouch is often assigned to audial effects that
feature a Low-Frequency Oscillator, such as tremolo or vibrato.
Patch Change messages are to change the sound, or patches, generated from the
instrument. Patch Change messages only contain 1 Data byte which enables a user
to select from 128 patches if the instrument has that many. While the message
seems uncomplex, it is very useful to a user as it allows them to switch patches while
in a performance, which could be automated so the sounds switch automatically.
The Pitch Bend Change message adjusts the pitch of the sound used by use of a
Pitch Bend Wheel. As Huber (2007) said, “… the ear can be extremely sensitive to
changes in pitch”. Because of this, the Pitch Bend Change message uses two data
bytes for one parameter (Fig. 8), resulting in a range of 16,384 steps, however since
Pitch Bend Change also allows for the pitch to descend, this range is more
realistically -8192 values downwards and +8192 values upwards, with 0 being the
unaltered pitch and the centre position of the control (Huber, 2007, p29).
Figure 8. Pitch Bend Range And Two Data Bytes
System messages do not contain MIDI Channels in the Status byte as they are sent
to all channels, or all devices in the network. System messages are split into two
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categories, System-Common and System Real-Time messages. With the exception
of System-Exclusive messages, they do not contain data associated with the
performance of an instrument, such as playing the keys on a MIDI keyboard, but are
more suited for the global operation of a setup, such as setting the song position
(Song Position Pointer Messages), syncing the clock timing between devices (Timing
Clock Messages) and resetting instruments to their initial power-up settings (System
Reset Messages). (Huber, 2007, p43 – p44)
Control Change (CC), or Continuous Controller, messages are associated with real-
time performance parameters, such as the panning of a sound (CC10), modulation
(CC1) and the Channel Volume (CC7). It uses a Controller ID in the Status byte to
associate which parameter to change.
The Modulation Wheel, or Mod Wheel, is CC1 and when applied, it introduces a
vibrato effect by use of a Low Frequency Oscillator; the intensity of the effect being
stronger the more the control is applied.
Damper Pedal (CC64), Portamento (CC65), Sustenuto (CC66), Soft Pedal (CC67),
Legato Footswitch (CC68) and Hold 2 (CC69) are Switch Controllers, being either
‘On’ or ‘Off’. Usually any Data byte value below 64 will turn the effect off whereas
any value above 64 will turn the effect on. The Damper Pedal will sustain the Note-
On command while the pedal is activated; only transmitting a Note-Off command
once the pedal is released. Sustenuto works like the Damper Pedal, except “… it will
only sustain notes that are currently being played” (Huber, 2007, p37).
All Notes Off (CC123) will send a Note-Off message to all 128 notes on all channels
as a ‘panic’ system in case the system didn’t receive a Note-Off message when it
was supposed to.
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Omni Mode, CC124 for ‘Off' and CC125 for ‘On’, transmits all data to all MIDI
channels when ‘On’, whereas the ‘Off’ setting will only transmit the data to one
channel.
There are a wide number of control devices available which one could make use of
to record a performance into MIDI data.
As stated by the MMA (MIDI Manufacturers Association, 2012b), “MIDI was primarily
designed for ‘keyboard players’…”. However, there is a wide range of MIDI
controllers available, from basic input systems to some that are more suited for niche
markets. Performance controllers are electronic instruments which can be played
real-time or used to record a performance into MIDI messages.
MIDI Drum Pads controllers, such as the Akai Professional MPC-500 (Fig 9.a), and
MIDI-enabled Electronic Drum Kits, such as the Roland TD-11K (Fig 9.b), are
controllers that are more suited to drumming, or percussive, techniques of playing.
These controllers generally consist of multiple ‘pads’, a flat surface area which
contain sensors to detect impact force, and are physically hit with to generate MIDI
data. The impact generates a MIDI Note-On channel message, the MIDI Note Pitch
being the sound that should be triggered, and the velocity, determined by the
pressure of the impact being higher the harder the pad is struck, which can be
assigned to any parameters that the sound source contains but is generally set to
intensity or amplitude of the playing sound.
The Electronic Drum-kits available are the same size of a real drum-kit and have a
distinct advantage over an acoustic drum set. As sound is generated through the
sound module which the MIDI drum kit is connected to, the artist has the ability to
change the sounds triggered by the pads to whatever their sound source allows,
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whereas a musician playing on an acoustic drum kit is bound by the current setup at
the time of performance.
Figure 9. MIDI Drum Controllers
“Wind instruments have a number of performance techniques that do not have a
keyboard equivalent – like pitch-pending, changing the timbre or producing
harmonics, all by using extra breath pressure and lip techniques” (Russ, 2007).
‘Wind MIDI Controllers’, otherwise known as a ‘wind synthesizer’ or ‘Electronic Wind
Instrument’, such as the Yamaha WX5, are played like a woodwind instrument.
The unique aspect of this instrument is the ‘breath sensor’ and Breath message
(CC2); the musician blows into the mouthpiece of the instrument and a pressure
sensor inside the instrument measures the force of the musicians breath which is
converted into the corresponding MIDI data. The Breath message is commonly used
to affect the amplitude of the sound, however some devices such as the Akai EWI
4000s utilise MIDI 2.0 which combine the messages of Breath (CC2), Volume (CC7),
Expression (CC11), Aftertouch (Channel Voice message 6) and Velocity (2nd Data
byte of Note-On, Channel Voice Message 2). There is also a lip sensor which will
commonly affect the pitch of the sound, Channel Voice message 7. (Batzdorf, 2006)
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Figure 10. MIDI ‘Wind Synths’
There are also MIDI controllers suited more for life performance and the operation of
playback events associated with sequencing. ‘Live Performance Controllers’, such
as Novation Launchpad, have buttons which send MIDI data to play sounds or
looped audio files within a DAW project. In the case of the Novation Launchpad, the
‘loops’ or sounds within the DAW are triggered via MIDI Note-on and MIDI Note-off
messages. (Novation, 2012)
Logic Pro, a DAW; an Apple iMac; a FireWire audio interface, the Focusrite Saffire
PRO 40; and a performance controller with slider controls, the Roland PCR-500, was
used to modify and manipulate MIDI data to compose a song. (Fig. 11)
Figure 11. PCR-500 Used In Logic Pro
“I happen to think that computers are the most important thing to happen to
musicians since the invention of cat-gut...” – Dr Robert Arthur “Bob” Moog (1990)
The Environment, in Logic Pro, was utilised to manipulate real-time MIDI data. The
result from the MIDI routing in the Environment was that a single Note-On Channel
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Voice message would produce a musical triad, as well as replicate these 3 MIDI
Channel Voice messages an octave above and an octave below.
To achieve this, the musical note in the first Data byte of the Note-On message
would be routed into a device called the Chord Memoriser, which allows one to
substitute the Note-On MIDI Pitch Number with a different Pitch Number or have
selected Pitch Numbers added to the performance of the initial musical note played.
The respective musical 3rd and 5th were added to each key, resulting in each single
Note-On Channel Voice message playing a 1,3,5 triad.
This triad, being sent as a 3 separate Note-On messages, in Logic Pro, was then
duplicated and sent into a MIDI data manipulator in Logic Pro, known as the
“Transformer”. The MIDI Pitch Number in the Note-On message was raised or
lowered 12 semitones, being an octave. When a performer is to push a single note
on a keyboard controller 9 MIDI Note-On messages are generated.
Figure 12 . Environment ‘Patch’
For two of the software synthesizers, an “Arpeggiator” was added to the above
manipulation process. An Arpeggiator repeats a note, or sequence of notes. When
only using one note, the Arpeggiator will only repeat that note. When playing more
than one note, the Arpeggiator will play a sequence consisting of the notes in the
chord played. The order of the pattern, the length of the notes and speed at which
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the arpeggio plays is defined via parameters within the Arpeggiator object in Logic
Pro.
In one of the sounds, this was utilised with the above Environment ‘patch’ to create a
‘chip-tune’, made infamous by 8-bit TV games, by having an incredibly fast
resolution, being note divisions every 1/128th , and short note length, 1/256th notes.
(Fig. 13)
Figure 13. Arpeggio
The hi-hat cymbals in the drum track initially had fixed velocity values throughout its
pattern in the sequencer. The velocity values of the MIDI notes in the sequencer
were altered as to create a groove, similar to the performance of a real drummer in
which every drum hit doesn’t sound exactly the same. (Fig. 14)
Figure 14. No Corrective Manipulation And Corrective Manipulation
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The performance MIDI controller was configured so that chosen controls on the
instrument, the sliders, would send the correct MIDI message to modify a parameter
in the DAW. One slider was assigned to the CC16, which is a General Purpose CC
message, and through the use of MIDI Learn within Logic Pro, was set to the ‘Filter
Blend’ within the chosen ES2 instrument, ‘Lead – Rhythmic’. The slider was adjusted
from its top position, being 127 in the message’s Data byte, to the lowest position,
being 0. The choice of using the slider was so there was less of a linear feel to the
diminution of the parameter.
The resulting effect on the sound was that there was a shift between 2 filters, going
from a low-pass filter (Filter 2) to a high-pass filter (Filter 1), resulting in the software
synthesizer producing higher harmonics. The MIDI controller was then used to
record automation data, CC16 affecting Filter Blend, into the sequencer of the DAW,
allowing for finer adjustments when compared to using a standard computer
peripheral such as a computer mouse. (Fig. 15)
Figure 15. Automation Via MIDI Controller
MIDI has proven to be a strong standardisation protocol, being 29 years old in 2012,
and in most cases, MIDI version 1.0 is still being utilised. It has remarkably changed
the way musicians compose their music, being a key player in the birth of many new
genres of music.
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MIDI has allowed for the layperson with simple music knowledge to be able to freely
express their creative side and compose music, where this may not have been
possible without the invention of MIDI. As more and more devices are released with
MIDI compatibility, it becomes a more and more useful tool to learn and understand.
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