lua_opdef
lua_opdef — Define an opcode in Lua at i-rate. The opcode can take any number of output and/or input arguments of any type.
Description
Define an opcode in Lua at i-rate. The opcode can take any number of output and/or input arguments of any type. The code is executed at initialization time, typically from the orchestra header. Global and local variables, functions, tables, and classes may be declared and defined. Objects defined at global Lua scope remain in scope throughout the performance, and are visible to any other Lua code in the same Csound thread.
![[Note]](images/note.png)
|
Note |
|---|---|
|
By default, all objects defined in Lua are defined at global scope. In order to ensure that objects are confined to their own block of code, that is to ensure that the object is visible only in lexical scope, the object must be declared as local. This is the feature of Lua that beginners tend to find the most troublesome. Another thing to look out for is that Lua arrays use 1-based indexing, not the 0-based indexing used in C and many other programming languages. |
Initialization
Sname -- The name of the opcode.
Sluacode -- A block of Lua code, of any
length. Multi-line blocks may be enclosed in double braces
(i.e. {{ }}). This code is
evaluated once at initialization time.
The Lua code must define all functions that will be called from Csound, using the following naming convention, where opcodename stands for the actual opcode name:
-
opcodename_initfor the i-rate opcode subroutine. -
opcodename_kontrolfor the k-rate opcode subroutine. -
opcodename_audiofor the a-rate opcode subroutine. -
opcodename_noteofffor the note-off subroutine.
Each of these Lua functions will receive three lightuserdata (i.e. pointer) arguments: the CSOUND object, the opcode instance, and a pointer to the opcode arguments, which the Lua code must be type cast to a LuaJIT FFI ctype structure containing the opcode output arguments, input arguments, and state variables. Using LuaJIT FFI, the elements of this structure will be accessible as though they were Lua types.
Each of these Lua functions must return 0 for success or 1 for failure.
The Lua functions may do absolutely anything, although of course if real-time performance is expected, care must be taken to disable Lua garbage collection and observe other recommendations for real-time code.
Example
Here is an example of a Lua opcode, implementing a Moog ladder filter. For purposes of comparison, a user-defined opcode and the native Csound opcode that compute the same sound using the same algorithm also are shown, and timed. The example uses the file luamoog.csd.
Example 463. Example of a Lua opcode.
<CsoundSynthesizer> <CsInstruments> sr = 48000 ksmps = 100 nchnls = 1 gibegan rtclock lua_opdef "moogladder", {{ local ffi = require("ffi") local math = require("math") local string = require("string") local csoundApi = ffi.load('csound64.dll.5.2') ffi.cdef[[ int csoundGetKsmps(void *); double csoundGetSr(void *); struct moogladder_t { double *out; double *inp; double *freq; double *res; double *istor; double sr; double ksmps; double thermal; double f; double fc; double fc2; double fc3; double fcr; double acr; double tune; double res4; double input; double i; double j; double k; double kk; double stg[6]; double delay[6]; double tanhstg[6]; }; ]] local moogladder_ct = ffi.typeof('struct moogladder_t *') function moogladder_init(csound, opcode, carguments) local p = ffi.cast(moogladder_ct, carguments) p.sr = csoundApi.csoundGetSr(csound) p.ksmps = csoundApi.csoundGetKsmps(csound) if p.istor[0] == 0 then for i = 0, 5 do p.delay[i] = 0.0 end for i = 0, 3 do p.tanhstg[i] = 0.0 end end return 0 end function moogladder_kontrol(csound, opcode, carguments) local p = ffi.cast(moogladder_ct, carguments) -- transistor thermal voltage p.thermal = 1.0 / 40000.0 if p.res[0] < 0.0 then p.res[0] = 0.0 end -- sr is half the actual filter sampling rate p.fc = p.freq[0] / p.sr p.f = p.fc / 2.0 p.fc2 = p.fc * p.fc p.fc3 = p.fc2 * p.fc -- frequency & amplitude correction p.fcr = 1.873 * p.fc3 + 0.4955 * p.fc2 - 0.6490 * p.fc + 0.9988 p.acr = -3.9364 * p.fc2 + 1.8409 * p.fc + 0.9968 -- filter tuning p.tune = (1.0 - math.exp(-(2.0 * math.pi * p.f * p.fcr))) / p.thermal p.res4 = 4.0 * p.res[0] * p.acr -- Nested 'for' loops crash, not sure why. -- Local loop variables also are problematic. -- Lower-level loop constructs don't crash. p.i = 0 while p.i < p.ksmps do p.j = 0 while p.j < 2 do p.k = 0 while p.k < 4 do if p.k == 0 then p.input = p.inp[p.i] - p.res4 * p.delay[5] p.stg[p.k] = p.delay[p.k] + p.tune * (math.tanh(p.input * p.thermal) - p.tanhstg[p.k]) else p.input = p.stg[p.k - 1] p.tanhstg[p.k - 1] = math.tanh(p.input * p.thermal) if p.k < 3 then p.kk = p.tanhstg[p.k] else p.kk = math.tanh(p.delay[p.k] * p.thermal) end p.stg[p.k] = p.delay[p.k] + p.tune * (p.tanhstg[p.k - 1] - p.kk) end p.delay[p.k] = p.stg[p.k] p.k = p.k + 1 end -- 1/2-sample delay for phase compensation p.delay[5] = (p.stg[3] + p.delay[4]) * 0.5 p.delay[4] = p.stg[3] p.j = p.j + 1 end p.out[p.i] = p.delay[5] p.i = p.i + 1 end return 0 end }} /* Moogladder - An improved implementation of the Moog ladder filter DESCRIPTION This is an new digital implementation of the Moog ladder filter based on the work of Antti Huovilainen, described in the paper \"Non-Linear Digital Implementation of the Moog Ladder Filter\" (Proceedings of DaFX04, Univ of Napoli). This implementation is probably a more accurate digital representation of the original analogue filter. This is version 2 (revised 14/DEC/04), with improved amplitude/resonance scaling and frequency correction using a couple of polynomials,as suggested by Antti. SYNTAX ar Moogladder asig, kcf, kres PERFORMANCE asig - input signal kcf - cutoff frequency (Hz) kres - resonance (0 - 1). CREDITS Victor Lazzarini */ opcode moogladderu, a, akk asig, kcf, kres xin setksmps 1 ipi = 4 * taninv(1) /* filter delays */ az1 init 0 az2 init 0 az3 init 0 az4 init 0 az5 init 0 ay4 init 0 amf init 0 if kres > 1 then kres = 1 elseif kres < 0 then kres = 0 endif /* twice the \'thermal voltage of a transistor\' */ i2v = 40000 /* sr is half the actual filter sampling rate */ kfc = kcf/sr kf = kcf/(sr*2) /* frequency & amplitude correction */ kfcr = 1.8730 * (kfc^3) + 0.4955 * (kfc^2) - 0.6490 * kfc + 0.9988 kacr = -3.9364 * (kfc^2) + 1.8409 * kfc + 0.9968; /* filter tuning */ k2vg = i2v * (1 - exp(-2 * ipi * kfcr * kf)) /* cascade of 4 1st order sections */ ay1 = az1 + k2vg * (tanh((asig - 4 * kres * amf * kacr) / i2v) - tanh(az1 / i2v)) az1 = ay1 ay2 = az2 + k2vg * (tanh(ay1 / i2v) - tanh(az2 / i2v )) az2 = ay2 ay3 = az3 + k2vg * (tanh(ay2 / i2v) - tanh(az3 / i2v)) az3 = ay3 ay4 = az4 + k2vg * (tanh(ay3 / i2v) - tanh(az4 / i2v)) az4 = ay4 /* 1/2-sample delay for phase compensation */ amf = (ay4 + az5) *0.5 az5 = ay4 /* oversampling */ ay1 = az1 + k2vg * (tanh((asig - 4 * kres * amf * kacr) / i2v) - tanh(az1 / i2v)) az1 = ay1 ay2 = az2 + k2vg * (tanh(ay1 / i2v) - tanh(az2 / i2v )) az2 = ay2 ay3 = az3 + k2vg * (tanh(ay2 / i2v) - tanh(az3 / i2v)) az3 = ay3 ay4 = az4 + k2vg * (tanh(ay3 / i2v) - tanh(az4 / i2v)) az4 = ay4 amf = (ay4 + az5) * 0.5 az5 = ay4 xout amf endop instr 1 prints "No filter.\n" kfe expseg 500, p3*0.9, 1800, p3*0.1, 3000 kenv linen 10000, 0.05, p3, 0.05 asig buzz kenv, 100, sr/(200), 1 ; afil moogladder asig, kfe, 1 out asig endin instr 2 prints "Native moogladder.\n" kfe expseg 500, p3*0.9, 1800, p3*0.1, 3000 kenv linen 10000, 0.05, p3, 0.05 asig buzz kenv, 100, sr/(200), 1 afil moogladder asig, kfe, 1 out afil endin instr 3 prints "UDO moogladder.\n" kfe expseg 500, p3*0.9, 1800, p3*0.1, 3000 kenv linen 10000, 0.05, p3, 0.05 asig buzz kenv, 100, sr/(200), 1 afil moogladderu asig, kfe, 1 out afil endin instr 4 prints "Lua moogladder.\n" kres init 1 istor init 0 kfe expseg 500, p3*0.9, 1800, p3*0.1, 3000 kenv linen 10000, 0.05, p3, 0.05 asig buzz kenv, 100, sr/(200), 1 afil init 0 lua_ikopcall "moogladder", afil, asig, kfe, kres, istor out afil endin instr 5 giended rtclock ielapsed = giended - gibegan print ielapsed gibegan rtclock endin </CsInstruments> <CsScore> f 1 0 65536 10 1 i 5.1 0 1 i 4 1 20 i 5.2 21 1 i 4 22 20 i 5.3 42 1 i 2 43 20 i 5.4 63 1 i 2 64 20 i 5.5 84 1 i 3 85 20 i 5.6 105 1 i 3 106 20 i 5.7 126 1 i 1 127 20 i 5.8 147 1 i 1 148 20 i 5.9 168 1 i 4 169 20 i 4 170 20 i 4 171 20 e </CsScore> </CsoundSynthesizer>