midichannelaftertouch is designed to simplify writing instruments that can be used interchangeably for either score or MIDI input, and to make it easier to adapt instruments originally written for score input to work with MIDI input.
In general, it should be possible to write instrument definitions that work identically with both scores and MIDI, including both MIDI files and real-time MIDI input, without using any conditional statements, and that take full advantage of MIDI voice messages.
Note that correlating Csound instruments with MIDI channel numbers is done using the massign opcode for real-time performance,. For file-driven performance, instrument numbers default to MIDI channel number + 1, but the defaults are overridden by any MIDI program change messages in the file.
ilow (optional) -- optional low value after rescaling, defaults to 0.
ihigh (optional) -- optional high value after rescaling, defaults to 127.
xchannelaftertouch -- returns the MIDI channel aftertouch during MIDI activation, remains unchanged otherwise.
If the instrument was activated by MIDI input, the opcode overwrites the value of xchannelaftertouch with the corresponding value from MIDI input. If the instrument was NOT activated by MIDI input, the value of xchannelaftertouch remains unchanged.
This enables score p-fields to receive MIDI input data during MIDI activation, and score values otherwise.
Adapting a score-activated Csound instrument.: To adapt an ordinary Csound instrument designed for score activation for score/MIDI interoperability:
Change all linen, linseg, and expseg opcodes to linenr, linsegr, and expsegr, respectively, except for a de-clicking or damping envelope. This will not materially change score-driven performance.
Add the following lines at the beginning of the instrument definition:
Obviously, midinoteoncps could be changed to midinoteonoct or any of the other options, and the choice of p-fields is arbitrary.; Ensures that a MIDI-activated instrument ; will have a positive p3 field. mididefault 60, p3 ; Puts MIDI key translated to cycles per ; second into p4, and MIDI velocity into p5 midinoteoncps p4, p5
Here is an example of the midichannelaftertouch opcode. It uses the files midichannelaftertouch.orc and midichannelaftertouch.sco.
Example 15-1. Example of the midichannelaftertouch opcode.
/* midichannelaftertouch.orc */
; Initialize the global variables.
sr = 44100
kr = 4410
ksmps = 10
nchnls = 1
; Instrument #1.
instr 1
kaft init 0
midichannelaftertouch kaft
; Display the aftertouch value when it changes.
printk2 kaft
endin
/* midichannelaftertouch.orc */
/* midichannelaftertouch.sco */
; Play Instrument #1 for ten seconds.
i 1 0 10
e
/* midichannelaftertouch.sco */
i1 127.00000 i1 20.00000 i1 44.00000