MIDI Controllers
Introduction
This section of Music Technology Handouts is about the master (or "mother") controller,
that is, the device used to control the rest of a MIDI setup.
- Keyboard controllers: examples
- Keyboard controllers: common features
Keyboard controllers
The most basic musical keyboards simply transmit note on/off, program change, and perhaps limited modulation data. They have unweighted keys (like an organ).
Example: Evolution MK-7 PC music keyboard.
- 37 Mini Keys giving a range of 3 octaves
- built-in MIDI cable
- supplied with software to access any SoundBlaster compatible sound card fitted to a PC
- price guide: £35.00 Stirling / $50.00 US
Evolution MK-7 PC music keyboard
More expensive keyboards include such features as key velocity,
a number of assignable modulation controls and song select for calling up sequences from the keyboard.
Example: Evolution MK-149 MIDI Keyboard
- 49 full size keys giving a range of 4 octaves
- velocity sensitive keys
- standard MIDI connection
- pitch bend wheel
- modulation wheel
- channel select
- program select
- transpose
- LED display
- socket for sustain pedal
- unweighted keys
- price guide: £120 / $160 Further details.
Evolution Keyboard Mk 149
Some more expensive keyboards have weighted keys which simulate the mechanical hammer action of a real piano.
Example: Roland A33
- 76 full size keys giving a range of over 6 octaves
- velocity sensitive keys
- 2 MIDI outs, 1 in, 1 thru
- 2 key zones
- transpose octave up or down
- pitch bend/modulation lever
- sockets for optional sustain switch and optional expression pedal
- weighted keys
- price guide: £400
The Roland AX-1 controller is a shoulder hung version of the A33.
Some controllers are available with aftertouch.
Example: Roland A90
- 88 full size keys giving a range of over 7 octaves
- velocity sensitive keys
- 4 separate MIDI outputs, 2 ins, 1 thru
- pitch bend / modulation wheels
- breath control
- up to 8 keyboard zones
- transpose
- backlit 3 character and 17 character LCD displays
- sockets for 2 foot switches, 2 foot controllers,volume pedal, breath controller
- aftertouch sensitive
- hammer action keys
- memory card port
- model A90EX, is as above plus VE-RD1 expansion board (piano sound source)
- price guide (A90): £1700 Further details
Roland A90 Keyboard Controller
Common controller features
Pitch bend
Moving a wheel in one direction raises the pitch of notes.
Moving the pitch wheel in the opposite direction lowers the pitch.
The pitch bend range is often adjustable. For example maximum travel of the wheel might be set to change the pitch by as little as a tone or as much as an octave.
When released, pitch bend wheels self-centre at the normal pitch.
On some controllers, pitch bend can be made to effect either the lowest note of a chord, or the highest, or all the notes.
Enthusiastic operation of the pitch bend wheel produces vast amounts of MIDI data which in turn uses up a lot of storage space in a sequencer. Glitches may also occur, as the system struggles to transmit all the data.
Portamento
Portamento is the effect produced when one note is carried smoothly on to the next with no gap. The pitches in between printed notes are briefly sounded. Stringed instruments and the trombone often use this very legato effect.
Portamento might occur on all the played notes or it might only occur if the previously played note is held down while the next one is played. The portamento time is the time taken for the pitch to completely change from one note to the next.
Modulation
Modulation occurs when one wave impresses its characteristics on another wave of higher frequency. The higher frequency wave is called the carrier wave; the lower frequency wave is called the modulating wave.
LFO (Low Frequency Oscillator)
Low frequency oscillators produce a variety of waveforms with frequencies ranging from approximately 0.001 Hz to 55Hz. In synthesizers, a low frequency oscillator is used to produce a modulating wave. The modulating wave can be used to produce 3 types of musical effects; vibrato, tremolo and phase effects.
Vibrato and tremolo are both effects used by singers and players of stringed instruments. Used carefully, these effects can make electronic instruments sound more like acoustic instruments.
Vibrato
Vibrato is a very slight changing of the pitch of a note, alternately above and below the true pitch.
String players achieve this effect by the controlled vibration of the finger stopping a string.
Vibrato is achieved in an electronic instrument by applying the (modulating) wave from the LFO to a selected voice.
A number of variables interact to determine how the LFO affects the vibrato of the selected voice...
- the sensitivity of the circuit (operator) to which the pitch modulation is applied
- the depth of the pitch variation i.e. how much the pitch varies from the true pitch of the note.
- the modulation delay
- When a 'note on' coincides with a positive peak in the wave from the LFO, the note produced will have a clear attack, like a piano note.
- If the LFO wave starts randomly, the effect is diffuse, like a chorus.
- If vibrato is delayed up to a few seconds, natural brass sounds can be achieved.
Modulation sensitivity and modulation depth are linked; the greater the sensitivity, the greater the pitch variation for a given depth setting.
Tremolo
Tremolo is the rapid repetition of a note.
Bowed stringed instrument players produce tremolo by rapidly moving the bow a short distance back and forward against a string. Electronic keyboards achieve the same effect by using the modulating wave (from the LFO) to rapidly alter the amplitude of the chosen voice.
The way in which tremolo is applied to the selected voice depends on two interrelated variables...
- the modulation sensitivity of the operator to which amplitude modulation is being applied
- the depth of variation of amplitude caused by the LFO i.e. the change in loudness as the note is rapidly reiterated.
Phase effects (Wah Wah e.t.c.)
When LFO is applied to a carrier, tremolo results. If LFO is applied instead to a modulator, cyclic variations in sound quality (timbre) occur. The type of effect depends on the waveform of the LFO (squarewave, triangular wave, sawtooth, sinewave e.t.c.) as well as its frequency.
Vibrato, tremolo and phase effects may be preset by the player using buttons and sliders. They can also be varied during performance by using the modulation wheel, a foot pedal, a knee lever or a breath controller.
Breath controllers
Some keyboards allow musical expression to be varied by blowing into a mouthpiece. This is akin to playing a wind instrument. The breath controller can duplicate the functions of the modulation wheel (adjusting vibrato, tremolo, wah wah).
Breath pressure can also be used to control the pitch, loudness or quality of a voice. Here the LFO plays no part. The breath pressure directly controls the pitch, loudness e.t.c. Breath controllers also permit tonguing effects. These make wind instrument sounds more realistic.
Key velocity control
When a key is struck hard, on a conventional piano, a hammer moves rapidly to strike a string. The more rapidly the hammer moves (the greater its velocity) the louder a note will sound. Electronic keyboards that respond in a similar manner to a piano (i.e. to the force with which their keys are struck) are said to be velocity sensitive. It is necessary that...
- the keying mechanism of the keyboard is velocity sensitive
- the voice generators can accept velocity information
Sometimes synthesizers are fitted with velocity sensitive generators even though their keyboards are not velocity sensitive.
Scaling
Level scaling
A feature of acoustic instruments that we might take for granted is that the loudness of notes decreases as the pitch increases. The thinner (treble) strings on an acoustic piano are doubled and in some places tripled to compensate for this decrease in output level. Nevertheless the higher strings still sound quieter. To imitate this effect on electronic keyboards an adjustment or "weighting" is applied. This adjustment is known as level (loudness) scaling. The higher notes on a keyboard become less audible as the amount of level scaling is increased.
Rate scaling
Higher pitched notes also have shorter volume and timbre envelopes. These higher notes therefore fade away quicker and the timbre (quality) changes faster. Rate scaling is the shortening of the length of the volume envelopes and timbre envelopes as notes are played higher up the keyboard.
Transposing
Transposition is the changing of the key of a piece of music. Usually, on a modern keyboard, the pitch of the entire keyboard, or sections of it, can be raised or lowered in semitone steps by a couple of octaves or more. This facility allows a modest 4 octave keyboard to play the notes found on instruments with a lower or higher range. Transposing also allows a musician to play in "difficult" keys (eg. ones with several sharps or flats) while using "easy" fingering (eg. the white notes of C major).
Master tuning
There is an international agreement that the pitch of the note A on the second space of the treble staff (stave) is 440 Hz. This is sometimes referred to as "concert pitch" and, of course, it establishes the pitches of all the other notes.
Sometimes you might want to alter the tuning of a keyboard, for example when playing along with a conventional piano that is not at concert pitch. The master tuning facility allows the pitch of a keyboard to be increased or decreased in small increments up to a maximum of a semitone.
Aftertouch
Also known as pressure sensitivity. A MIDI control signal is transmitted after a key has been depressed. The greater the pressure on the key, the greater the value of the signal transmitted to the voice modules.
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