Aftertouch
As aftertouch in electronic refers to keyboard instruments such as synthesizers or keyboards to control by pressure applied to the keyboard pressure. Pressing the key more or less after the actual key press continuously generates additional signals that are used to modulate tone or timbre - such as the pitch, the intensity of a vibrato, the volume, but also the waveform or filter used.
When using MIDI devices in particular , it is important to distinguish between two types of aftertouch:
- Monophonic aftertouch ("Channel Aftertouch"), in which the pressure value has the same effect on all notes transmitted in the respective MIDI channel
- polyphonic aftertouch that is transmitted individually for each note
technology
Polyphonic aftertouch was already possible with the Yamaha CS-80 . Most keyboards available on the market are only able to generate monophonic aftertouch signals, since the generation of pressure values for each individual key is significantly more complex.
As a rule, there is an element across the entire width of the keyboard that changes its electrical resistance or capacitance under the action of force. FSR elements or two metal strips that are separated by an insulating layer and form a capacitor are often used for this . The use of piezo elements is also possible; Simple piezo sound generators, which are cheap and easily available, were used for the doepfer LMK3 master keyboard .
Polyphonic keyboards often use a method with which the touch dynamics and pressure on the key can be measured; Examples are the capacitive keyboard of the Arturia MicroFreak synthesizer or controllers based on drum pads, such as the checkerboard launchpad keyboards from Novation . MIDI retrofit kits for Rhodes electric pianos are based on infrared sensors.
Devices such as the Roli Seaboard, the Haken Continuum Synthesizer or the Linnstrument also use polyphonic aftertouch to shape the sound. There the MIDI extension MPE is used to transmit the control signals.
Transmission via MIDI
In the MIDI standard, the pressure information is not transmitted as a controller value (Continuous Controller, CC) with the command code 0xBn 0xvv (n stands for the MIDI channel, vv for the 7-bit value of the controller), as is usually the case own commands:
- Channel aftertouch: 0xDn 0xvv (n = MIDI channel, vv = aftertouch value)
- Polyphonic aftertouch: 0xAn 0xkk 0xvv (n = MIDI channel, kk = note, vv = aftertouch value)
As with the CC command, control signals can be transmitted with a maximum of 7 bit resolution, i.e. values from 0-127.
Relationship to MPE
The MPE standard was defined in 2018 as an alternative to polyphonic aftertouch . In this extension of the MIDI definition, a sound is assigned several MIDI channels on a device, so that individual controller and aftertouch values can be transmitted for each note via its respective channel. MPE uses channel aftertouch messages, which are generated and transmitted polyphonically on several MIDI channels.
Individual evidence
- ↑ Open Music Labs FSR Tutorial
- ↑ http://www.doepfer.de/service/LMK3V2_Service.pdf
- ↑ http://www.tasteundtechnik.de/117101.html
- ↑ Summary of MIDI Messages. The Midi Association, accessed January 24, 2020 .