Macros within Csound provide a mechanism whereby a line or a block of code can be referenced using a macro codeword. Whenever the user-defined macro codeword for that block of code is subsequently encountered in a Csound orchestra or score it will be replaced by the code text contained within the macro. This mechanism can be extremely useful in situations where a line or a block of code will be repeated many times - if a change is required in the code that will be repeated, it need only be altered once in the macro definition rather than having to be edited in each of the repetitions.
Csound utilises a subtly different mechanism for orchestra and score macros so each will be considered in turn. There are also additional features offered by the macro system such as the ability to create a macro that accepts arguments - which can be thought of as the main macro containing sub-macros that can be repeated multiple times within the main macro - the inclusion of a block of text contained within a completely separate file and other macro refinements.
It is important to realise that a macro can contain any text, including carriage returns, and that Csound will be ignorant to its use of syntax until the macro is actually used and expanded elsewhere in the orchestra or score. Macro expansion is a feature of the orchestra and score parser and is not part of the orchestra performance time.
Macros are defined using the syntax:
#define NAME # replacement text #
'NAME' is the user-defined name that will be used to call the macro at some point later in the orchestra; it must begin with a letter but can then contain any combination of numbers and letters. A limited range of special characters can be employed in the name. Apostrophes, hash symbols and dollar signs should be avoided. 'replacement text', bounded by hash symbols will be the text that will replace the macro name when later called. Remember that the replacement text can stretch over several lines. A macro can be defined anywhere within the <CsInstruments> </CsInstruments> sections of a .csd file. A macro can be redefined or overwritten by reusing the same macro name in another macro definition. Subsequent expansions of the macro will then use the new version.
To expand the macro later in the orchestra the macro name needs to be preceded with a '$' symbol thus:
The following example illustrates the basic syntax needed to employ macros. The name of a sound file is referenced twice in the score so it is defined as a macro just after the header statements. Instrument 1 derives the duration of the sound file and instructs instrument 2 to play a note for this duration. instrument 2 plays the sound file. The score as defined in the <CsScore> </CsScore> section only lasts for 0.01 seconds but the event_i statement in instrument 1 will extend this for the required duration. The sound file is a mono file so you can replace it with any other mono file or use the original one.
<CsoundSynthesizer> <CsOptions> -odac </CsOptions> <CsInstruments> sr = 44100 ksmps = 16 nchnls = 1 0dbfs = 1 ; define the macro #define SOUNDFILE # "loop.wav" # instr 1 ; use an expansion of the macro in deriving the duration of the sound file idur filelen $SOUNDFILE event_i "i",2,0,idur endin instr 2 ; use another expansion of the macro in playing the sound file a1 diskin2 $SOUNDFILE,1 out a1 endin </CsInstruments> <CsScore> i 1 0 0.01 e </CsScore> </CsoundSynthesizer> ; example written by Iain McCurdy
In more complex situations where we require slight variations, such as different constant values or different sound files in each reuse of the macro, we can use a macro with arguments. A macro's arguments are defined as a list of sub-macro names within brackets after the name of the primary macro with each macro argument being separated using an apostrophe as shown below.
#define NAME(Arg1'Arg2'Arg3...) # replacement text #
Arguments can be any text string permitted as Csound code, they should not be likened to opcode arguments where each must conform to a certain type such as i, k, a etc. Macro arguments are subsequently referenced in the macro text using their names preceded by a '$' symbol. When the main macro is called later in the orchestra its arguments are then replaced with the values or strings required. The Csound Reference Manual states that up to five arguments are permitted but this still refers to an earlier implementation and in fact many more are actually permitted.
In the following example a 6 partial additive synthesis engine with a percussive character is defined within a macro. Its fundamental frequency and the ratios of its six partials to this fundamental frequency are prescribed as macro arguments. The macro is reused within the orchestra twice to create two different timbres, it could be reused many more times however. The fundamental frequency argument is passed to the macro as p4 from the score.
<CsoundSynthesizer> <CsOptions> -odac </CsOptions> <CsInstruments> sr = 44100 ksmps = 16 nchnls = 1 0dbfs = 1 gisine ftgen 0,0,2^10,10,1 ; define the macro #define ADDITIVE_TONE(Frq'Ratio1'Ratio2'Ratio3'Ratio4'Ratio5'Ratio6) # iamp = 0.1 aenv expseg 1,p3*(1/$Ratio1),0.001,1,0.001 a1 poscil iamp*aenv,$Frq*$Ratio1,gisine aenv expseg 1,p3*(1/$Ratio2),0.001,1,0.001 a2 poscil iamp*aenv,$Frq*$Ratio2,gisine aenv expseg 1,p3*(1/$Ratio3),0.001,1,0.001 a3 poscil iamp*aenv,$Frq*$Ratio3,gisine aenv expseg 1,p3*(1/$Ratio4),0.001,1,0.001 a4 poscil iamp*aenv,$Frq*$Ratio4,gisine aenv expseg 1,p3*(1/$Ratio5),0.001,1,0.001 a5 poscil iamp*aenv,$Frq*$Ratio5,gisine aenv expseg 1,p3*(1/$Ratio6),0.001,1,0.001 a6 poscil iamp*aenv,$Frq*$Ratio6,gisine a7 sum a1,a2,a3,a4,a5,a6 out a7 # instr 1 ; xylophone ; expand the macro with partial ratios that reflect those of a xylophone ; the fundemental frequency macro argument (the first argument - ; - is passed as p4 from the score $ADDITIVE_TONE(p4'1'3.932'9.538'16.688'24.566'31.147) endin instr 2 ; vibraphone $ADDITIVE_TONE(p4'1'3.997'9.469'15.566'20.863'29.440) endin </CsInstruments> <CsScore> i 1 0 1 200 i 1 1 2 150 i 1 2 4 100 i 2 3 7 800 i 2 4 4 700 i 2 5 7 600 e </CsScore> </CsoundSynthesizer> ; example written by Iain McCurdy
Score macros employ a similar syntax. Macros in the score can be used in situations where a long string of p-fields are likely to be repeated or, as in the next example, to define a palette of score patterns than repeat but with some variation such as transposition. In this example two 'riffs' are defined which each employ two macro arguments: the first to define when the riff will begin and the second to define a transposition factor in semitones. These riffs are played back using a bass guitar-like instrument using the wgpluck2 opcode. Remember that mathematical expressions within the Csound score must be bound within square brackets .
<CsoundSynthesizer> <CsOptions> -odac </CsOptions> <CsInstruments> sr = 44100 ksmps = 16 nchnls = 1 0dbfs = 1 instr 1 ; bass guitar a1 wgpluck2 0.98, 0.4, cpsmidinn(p4), 0.1, 0.6 aenv linseg 1,p3-0.1,1,0.1,0 out a1*aenv endin </CsInstruments> <CsScore> ; p4 = pitch as a midi note number #define RIFF_1(Start'Trans) # i 1 [$Start ] 1 [36+$Trans] i 1 [$Start+1 ] 0.25 [43+$Trans] i 1 [$Start+1.25] 0.25 [43+$Trans] i 1 [$Start+1.75] 0.25 [41+$Trans] i 1 [$Start+2.5 ] 1 [46+$Trans] i 1 [$Start+3.25] 1 [48+$Trans] # #define RIFF_2(Start'Trans) # i 1 [$Start ] 1 [34+$Trans] i 1 [$Start+1.25] 0.25 [41+$Trans] i 1 [$Start+1.5 ] 0.25 [43+$Trans] i 1 [$Start+1.75] 0.25 [46+$Trans] i 1 [$Start+2.25] 0.25 [43+$Trans] i 1 [$Start+2.75] 0.25 [41+$Trans] i 1 [$Start+3 ] 0.5 [43+$Trans] i 1 [$Start+3.5 ] 0.25 [46+$Trans] # t 0 90 $RIFF_1(0 ' 0) $RIFF_1(4 ' 0) $RIFF_2(8 ' 0) $RIFF_2(12'-5) $RIFF_1(16'-5) $RIFF_2(20'-7) $RIFF_2(24' 0) $RIFF_2(28' 5) e </CsScore> </CsoundSynthesizer> ; example written by Iain McCurdy
Score macros can themselves contain macros so that, for example, the above example could be further expanded so that a verse, chorus structure could be employed where verses and choruses, defined using macros, were themselves constructed from a series of riff macros.
UDOs and macros can both be used to reduce code repetition and there are many situations where either could be used with equal justification but each offers its own strengths. UDOs strengths lies in their ability to be used just like an opcode with inputs and outputs, the ease with which they can be shared - between Csound projects and between Csound users - their ability to operate at a different k-rate to the rest of the orchestra and in how they facilitate recursion. The fact that macro arguments are merely blocks of text, however, offers up new possibilities and unlike UDOs, macros can span several instruments. Of course UDOs have no use in the Csound score unlike macros. Macros can also be used to simplify the creation of complex FLTK GUI where panel sections might be repeated with variations of output variable names and location.
Csound's orchestra and score macro system offers many additional refinements and this chapter serves merely as an introduction to their basic use. To learn more it is recommended to refer to the relevant sections of the Csound Reference Manual.
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