OPCODE GUIDE: MATH, PYTHON/ SYSTEM, PLUGINS

MATH

• MATHEMATICAL CALCULATIONS

  • Arithmetic Operations
    

    +, -, *, /, ^, % are the usual signs for addition, subtraction, multiplication, division, raising to a power and modulo. The precedence is like that used in common mathematics (* binds stronger than + etc.), but you can change this behaviour with parentheses: 2^(1/12) returns 2 raised by 1/12 (= the 12st root of 2), while 2^1/12 returns 2 raised by 1, and the result divided by 12.

    exp(x), log(x), log10(x) and sqrt(x) return e raised to the xth power, the natural log of x, the base 10 log of x, and the square root of x.
    

    abs(x) returns the absolute value of a number.
    

    int(x) and frac(x) return the integer respective the fractional part of a number.
    

    round(x), ceil(x), floor(x) round a number to the nearest, the next higher or the next lower integer.

  • Trigonometric Functions

    sin(x), cos(x), tan(x) perform a sine, cosine or tangent function.
    

    sinh(x), cosh(x), tanh(x) perform a hyperbolic sine, cosine or tangent function.
    

    sininv(x), cosinv(x), taninv(x) and taninv2(x) perform the arcsine, arccosine and arctangent functions.

  • Logic Operators

    && and ||  are the symbols for a logical "and" and "or". Note that you can use here parentheses for defining the precedence, too, for instance: if (ival1 < 10 && ival2 > 5) || (ival1 > 20 && ival2 < 0) then ...

• CONVERTERS

  • MIDI To Frequency 

    cpsmidi converts a MIDI note number from a triggered instrument to the frequency in Hertz.

    cpsmidinn does the same for any input values (i- or k-rate).

    Other opcodes convert to Csound's pitch- or octave-class system. They can be found here.

  • Frequency To MIDI

    Csound has no own opcode for the conversion of a frequency to a midi note number, because this is a rather simple calculation. You can find a User Defined Opcode for rounding to the next possible midi note number or for the exact translation to a midi note number and a cent value as fractional part.

  • Cent Values To Frequency 

    cent converts a cent value to a multiplier. For instance, cent(1200) returns 2, cent(100) returns 1.059403. If you multiply this with the frequency you reference to, you get frequency of the note which corresponds to the cent interval.

  • Amplitude Converters

    ampdb returns the amplitude equivalent of the dB value. ampdb(0) returns 1, ampdb(-6) returns 0.501187, and so on.

    ampdbfs returns the amplitude equivalent of the dB value, according to what has been set as 0dbfs (1 is recommended, the default is 15bit = 32768). So ampdbfs(-6) returns 0.501187 for 0dbfs=1, but 16422.904297 for 0dbfs=32768.

    dbamp returns the decibel equivalent of the amplitude value, where an amplitude of 1 is the maximum. So dbamp(1) -> 0 and dbamp(0.5) -> -6.020600.

    dbfsamp returns the decibel equivalent of the amplitude value set by the 0dbfs statement. So dbfsamp(10) is 20.000002 for 0dbfs=0 but -70.308998 for 0dbfs=32768.

  • Scaling 

    Scaling of signals from an input range to an output range, like the "scale" object in Max/MSP, is not implemented in Csound, because it is a rather simple calculation. It is available as User Defined Opcode: Scali (i-rate), Scalk (k-rate) or Scala (a-rate).
    

PYTHON AND SYSTEM

• PYTHON OPCODES

  pyinit initializes the Python interpreter.
  

  pyrun runs a Python statement or block of statements.

  pyexec executes a script from a file at k-time, i-time or if a trigger has been received.

  pycall invokes the specified Python callable at k-time or i-time.

  pyeval evaluates a generic Python expression and stores the result in a Csound k- or i-variable, with optional trigger.

  pyassign assigns the value of the given Csound variable to a Python variable possibly destroying its previous content.

• SYSTEM OPCODES

  getcfg returns various Csound configuration settings as a string at init time.

  system / system_i call an external program via the system call.

PLUGINS

• PLUGIN HOSTING

  • LADSPA

    dssiinit loads a plugin.

    dssiactivate activates or deactivates a plugin if it has this facility.

    dssilist lists all available plugins found in the LADSPA_PATH and DSSI_PATH global variables.

    dssiaudio processes audio using a plugin.

    dssictls sends control information to a plugin's control port.

  • VST

    vstinit loads a plugin.

    vstaudio / vstaudiog return a plugin's output.

    vstmidiout sends midi data to a plugin.

    vstparamset / vstparamget sends and receives automation data to and from the plugin.

    vstnote sends a midi note with a definite duration.

    vstinfo outputs the parameter and program names for a plugin.

    vstbankload loads an .fxb bank.

    vstprogset sets the program in a .fxb bank.

    vstedit opens the GUI editor for the plugin, when available.