Linux MIDI: A Brief Survey, Part 4

Looking ahead to the next generation of MIDI music-making software, including Improv, Q-Midi and Csound.
Csound

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.

Output

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!

Dave Phillips is a musician, teacher and writer living in Findlay, Ohio. He has been an active member of the Linux audio community since his first contact with Linux in 1995. He is the author of The Book of Linux Music & Sound, as well as numerous articles in Linux Journal.

______________________

Similis sum folio de quo ludunt venti.

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Will Part 5 be available soon

jhansonxi's picture

Will Part 5 be available soon?

Which card should I buy?

Atle Weibell's picture

Hi,

Thanks for great articles! I have a USB Midisport 2x2, but it doesn't seem to be easy to setup in linux. I need a new sound card anyway, so I'll buy one with MIDI support as well. In an earlier comment, it was mentioned that not all vendors provide specifications. Who are the good guys? Which cards should I consider for MIDI and audio? :)

regards, aw

I just got a midisport 1x1 go

nick rout's picture

I just got a midisport 1x1 going last night on my laptop. The way to do it is described here:

http://usb-midi-fw.sourceforge.net/

I made my son laugh this morning - I went to wake him up and told him I had learned some new pieces on the electric piano last night. I dashed back to the music room, hit play in kmid and a beautiful Bach sonata thundered out. As I usually struggle with anything beyond "Twinkle Twinkle" he was impressed !

Rosegarden had compiled while I slept and we then successfully used the piano to input a couple of scales into Rosegarden turned them into notation, played them back as a trumpet on the computer.

So your midisport will work!

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