Linux MIDI: A Brief Survey, Part 4

The venerable Csound music and sound programming language has long supported MIDI input as MIDI files for play by Csound instruments or by a MIDI device for playing a Csound instrument by way of external hardware--keyboard, sequencer, wind controller. Thanks primarily to the work of developer Gabriel Maldonado, Csound also is a useful programming language for real-time MIDI output.

Playing a Csound instrument, an orc in Csound-speak, through an external MIDI device is a fairly simple procedure. The following orc file prepares a MIDI-sensitive instrument :

       instr 1 
inum   notnum			; receive MIDI note number
iamp   ampmidi	inum*50		; use it to set amplitude scaling
kfreq  cpsmidib			; convert MIDI note number to Hertz 
				   frequency value
a1     oscil	iamp,kfreq,1	; three detuned oscillators, each using a 
 			           different waveform (see score below)
a2     oscil	iamp,kfreq*1.003,2
a3      oscil	iamp,kfreq*.997,3
asig   =	a1+a2+a3	; audio signal equals sum of three oscillators
kenv   linenr	1,.07,.11,.01	; MIDI-controlled envelope for scaling output
       out	asig*kenv	; output equals oscillators shaped by envelope
       endin

Notice that once MIDI data is captured by Csound, it can be utilized for any purpose within an instrument design.

This code provides the Csound score file, a sco in Csound-speak, for this instrument :

f1 0 8192 10 .1 0 .2 0 0 .4 0 0 0 0 .8	; function tables for 
					    oscillator waveforms
f2 0 8192 10 1 0 .9 0 0 .7 0 0 0 .4
f3 0 8192 10 .5 0 .6 0 0 .3 0 0 0 .9
f0 10000		; placeholder to activate instrument 
					      for 10000 seconds
e			; end score

In classic Csound you would run this orc/sco like so:

csound -o devaudio -M /dev/midi -dm6

where -o determines the output target, -M selects a MIDI input device and -dm6 sets the graphics and messaging levels. Instrument, score and launch options all can be rolled into a single CSD file, a format that unifies Csound's necessary components into one handy form.

Designing a Csound instrument involves the definition and connection of components called opcodes. A Csound opcode could be an oscillator (oscil), an envelope generator (linenr, linseg), a mathematic operator (=), a MIDI capture function (ampmid, cpsmidib) or any of the hundreds of other functions and capabilities available as Csound opcodes.

The following CSD-formatted Csound code demonstrates the moscil opcode, a MIDI output function. The instrument, instr 1, transmits a major scale as a series of MIDI note messages starting from a given note-number, 48, and rising according to the envelope curve described by the linseg opcode.

<CsoundSynthesizer>

<CsOptions>
;;; The -Q flag selects a MIDI output port.
;;; An audio output device is required.
-Q0 -o devaudio -dm6
</CsOptions>

<CsInstruments>

       	sr=44100	; audio sampling rate, behaves as a 
			; tempo control for MIDI output
       	kr=44100	; signal control rate (equals sr 
			; for MIDI output best results)
        ksmps=1		; samples per control period
        nchnls=1	; number of audio channels

        instr 1
ival    =       48
	
kchn    =       0
knum    linseg 	ival,1,ival+2,1,ival+4,1,ival+5,1,ival+7,1,ival+9,1,
		ival+11,1,ival+12
kdur    =       .8
kpause  =       .2
        moscil  kchn,knum,44,kdur,kpause ; There is no audio 
						output stage.
        endin

</CsInstruments>
	
<CsScore>
i1 0 8
e
</CsScore>

</CsoundSynthesizer>

The linseg envelope generator creates a multistage envelope in which each step corresponds to a scale degree. When this file is run with csound moscil-test.csd, a C major scale is played by whatever instrument is receiving data on the MIDI interface selected by the -Q option.

Csound has many opcodes dedicated to the reception, transmission and alteration of MIDI messages. The possibilities are intriguing: simultaneous MIDI input/output, given two physical ports; MIDI control of synthesis parameters; instruments with combined audio/MIDI output; and even MIDI control by way of Csound's FLTK-based GUI opcodes. With Csound, your imagination is the limit.

In my next column, I'll finish this MIDI tour with a look at some GUI-based experimental MIDI applications, including Tim Thompson's KeyKit, Jeffrey Putnam's Grammidity and Elody from GRAME, the MidiShare people. See you next month!

Improv

jMusic

Q-Midi

Common Music

Notes From The Metalevel

Csound

MidiShare

"Linux MIDI: A Brief Survey, Part 3"

"Linux MIDI: A Brief Survey, Part 2"

"Linux MIDI: A Brief Survey, Part 1"