Defining opcodes

The opcode and endop statements allow defining a new opcode that can be used the same way as any of the built-in Csound opcodes. These opcode blocks are very similar to instruments (and are, in fact, implemented as special instruments), but cannot be called as a normal instrument e.g. with the i statements.

A user-defined opcode block must precede the instrument (or other opcode) from which it is used. But it is possible to call the opcode from itself. This allows recursion of any depth that is limited only by available memory.

Similarly to instruments, the variables and labels of a user-defined opcode block are local and cannot be accessed from the caller instrument (and the opcode cannot access variables of the caller, either).

Some parameters are automatically copied at initialization, however:

Also, the release flag (see the release opcode) is copied at performance time.

Modifying the note duration in the opcode definition by assigning to p3, or using ihold, turnoff, xtratim, linsegr, or similar opcodes will also affect the caller instrument. Changes to MIDI controllers (for example with ctrlinit) will also apply to the instrument from which the opcode was called.

Use the setksmps opcode to set the local ksmps value.

The xin and xout opcodes copy variables to and from the opcode definition, allowing communication with the calling instrument.

The types of input and output variables are defined by the parameters intypes and outtypes.

	Tip
	You can create UDOs which take no inputs or outputs by using 0 instead of a string.

	Notes
	xin and xout should be called only once, and xin should precede xout, otherwise an init error and deactivation of the current instrument may occur. These opcodes actually run only at i-time. Performance time copying is done by the user opcode call. This means that skipping xin or xout with kgoto has no effect, while skipping with igoto affects both init and performance time operation.

Syntax

opcode name, outtypes, intypes

Initialization

name -- name of the opcode. It may consist of any combination of letters, digits, and underscore but should not begin with a digit. If an opcode with the specified name already exists, it is redefined (a warning is printed in such cases). Some reserved words (like instr and endin) cannot be redefined.

intypes -- list of input types, any combination of the characters: a, f, k, O, P, V, K, i, o, p, and j. A single 0 character can be used if there are no input arguments. Double quotes and delimiter characters (e.g. comma) are not needed.

The meaning of the various intypes is shown in the following table:

outtypes -- list of output types. The format is the same as in the case of intypes.

Here are the available outtypes:

The maximum allowed number of output arguments is 256.

The input parameters can be read with xin, and the output is written by xout opcode. Only one instance of these units should be used, as xout overwrites and does not accumulate the output. The number and type of arguments for xin and xout must be the same as in the declaration of the user-defined opcode block (see tables above).

Performance

The syntax of a user-defined opcode block is as follows:

opcode  name, outtypes, intypes
xinarg1 [, xinarg2] [, xinarg3] ... [xinargN]  xin
[setksmps  iksmps]
... the rest of the instrument's code.
xout  xoutarg1 [, xoutarg2] [, xoutarg3] ... [xoutargN]
endop

The new opcode can then be used with the usual syntax:

[xoutarg1] [, xoutarg2] ... [xoutargN] name  [xinarg1] [, xinarg2] ... [xinargN]

	Note
	The opcode call is always executed both at initialization and performance time, even if there are no a- or k-rate arguments. If there are many user opcode calls that are known to have no effect at performance time in an instrument, then it may save some CPU time to jump over groups of such opcodes with kgoto.

Examples

Here is an example of a user-defined opcode. It uses the file opcode.csd.

<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac    ;;;realtime audio out
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o opcode_example.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

sr = 44100
ksmps = 32
nchnls = 2
0dbfs  = 1

/* example opcode 1: simple oscillator */

        opcode Oscillator, a, kk

kamp, kcps      xin             ; read input parameters
a1      vco2 kamp, kcps         ; sawtooth oscillator
        xout a1                 ; write output

        endop

/* example opcode 2: lowpass filter with local ksmps */

        opcode Lowpass, a, akk

        setksmps 1              ; need sr=kr
ain, ka1, ka2   xin             ; read input parameters
aout    init 0                  ; initialize output
aout    =  ain*ka1 + aout*ka2   ; simple tone-like filter
        xout aout               ; write output

        endop

/* example opcode 3: recursive call */

        opcode RecursiveLowpass, a, akkpp

ain, ka1, ka2, idep, icnt       xin     ; read input parameters
        if (icnt >= idep) goto skip1    ; check if max depth reached
ain     RecursiveLowpass ain, ka1, ka2, idep, icnt + 1
skip1:
aout    Lowpass ain, ka1, ka2           ; call filter
        xout aout                       ; write output

        endop

/* example opcode 4: de-click envelope */

        opcode DeClick, a, a

ain     xin
aenv    linseg 0, 0.02, 1, p3 - 0.05, 1, 0.02, 0, 0.01, 0
        xout ain * aenv         ; apply envelope and write output

        endop

/* instr 1 uses the example opcodes */

        instr 1

kamp    =  .7                ; amplitude
kcps    expon 50, p3, 500       ; pitch
a1      Oscillator kamp, kcps                   ; call oscillator
kflt    linseg 0.4, 1.5, 0.4, 1, 0.8, 1.5, 0.8  ; filter envelope
a1      RecursiveLowpass a1, kflt, 1 - kflt, 10 ; 10th order lowpass
a1      DeClick a1
        outs a1, a1

        endin


</CsInstruments>
<CsScore>

i 1 0 4
e5		;extra second before quitting

</CsScore>
</CsoundSynthesizer>

Here is another example of a user-defined opcode. It uses the file opcode_f.csd.

<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac    ;;;realtime audio out
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o opcode_f.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

sr = 44100
ksmps = 32
0dbfs =  1
nchnls = 2

; example by Luis Salgueiro and joachim heintz

opcode Transpose, a, fk    ; transpose a monophonic input signal through FFT.
  fsig, kInterval xin
  fScaled pvscale fsig, semitone(kInterval)
  aTransposed pvsynth fScaled
  xout aTransposed
endop

opcode Stretch,f,ik
  iTab, kSpeed xin
  fStretch pvstanal kSpeed, 1, 1, iTab
  xout fStretch
endop

giFox ftgen 0, 0, 0, 1, "fox.wav", 0, 0, 0

instr 1
  aSnd diskin2 "fox.wav"
  fSnd pvsanal aSnd, 1024, 256, 1024, 1
  aTransposed Transpose fSnd, p4   ; p4 = transposition in semitones
  outall aTransposed/2
endin

instr 2
  fStretch Stretch giFox, transeg:k(1,p3,-3,0)
  aStretch pvsynth fStretch
  outall aStretch
endin

</CsInstruments>
<CsScore>
i1 0 3 0
i1 . . 7
i1 . . 12
i2 4 8
e
</CsScore>
</CsoundSynthesizer>

See Also

endop, setksmps, xin, xout

Credits

Author: Istvan Varga, 2002; based on code by Matt J. Ingalls

New in version 4.22