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LOCAL AND GLOBAL VARIABLES
Variable Types
In Csound, there are several types of variables. It is important to understand the differences between these types. There are
- initialization variables, which are updated at each initialization pass, i.e. at the beginning of each note or score event. They start with the character i. To this group count also the score parameter fields, which always starts with a p, followed by any number: p1 refers to the first parameter field in the score, p2 to the second one, and so on.
- control variables, which are updated at each control cycle during the performance of an instrument. They start with the character k.
- audio variables, which are also updated at each control cycle, but instead of a single number (like control variables) they consist of a vector (a collection of numbers), having in this way one number for each sample. They start with the character a.
- string variables, which are updated either at i-time or at k-time (depending on the opcode which produces a string). They start with the character S.
Except these four standard types, there are two other variable types which are used for spectral processing:
- f-variables are used for the streaming phase vocoder opcodes (all starting with the characters pvs), which are very important for doing realtime FFT (Fast Fourier Transform) in Csound. They are updated at k-time, but their values depend also on the FFT parameters like frame size and overlap.
- w-variables are used in some older spectral processing opcodes.
The following example exemplifies all the variable types (except the w-type):
EXAMPLE 03B01_Variable_types.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 32
0dbfs = 1
nchnls = 2
seed 0; random seed each time different
instr 1; i-time variables
iVar1 = p2; second parameter in the score
iVar2 random 0, 10; random value between 0 and 10
iVar = iVar1 + iVar2; do any math at i-rate
print iVar1, iVar2, iVar
endin
instr 2; k-time variables
kVar1 line 0, p3, 10; moves from 0 to 10 in p3
kVar2 random 0, 10; new random value each control-cycle
kVar = kVar1 + kVar2; do any math at k-rate
; --- print each 0.1 seconds
printks "kVar1 = %.3f, kVar2 = %.3f, kVar = %.3f%n", 0.1, kVar1, kVar2, kVar
endin
instr 3; a-variables
aVar1 oscils .2, 400, 0; first audio signal: sine
aVar2 rand 1; second audio signal: noise
aVar3 butbp aVar2, 1200, 12; third audio signal: noise filtered
aVar = aVar1 + aVar3; audio variables can also be added
outs aVar, aVar; write to sound card
endin
instr 4; S-variables
iMyVar random 0, 10; one random value per note
kMyVar random 0, 10; one random value per each control-cycle
;S-variable updated just at init-time
SMyVar1 sprintf "This string is updated just at init-time:
kMyVar = %d\n", iMyVar
printf_i "%s", 1, SMyVar1
;S-variable updates at each control-cycle
printks "This string is updated at k-time:
kMyVar = %.3f\n", .1, kMyVar
endin
instr 5; f-variables
aSig rand .2; audio signal (noise)
; f-signal by FFT-analyzing the audio-signal
fSig1 pvsanal aSig, 1024, 256, 1024, 1
; second f-signal (spectral bandpass filter)
fSig2 pvsbandp fSig1, 350, 400, 400, 450
aOut pvsynth fSig2; change back to audio signal
outs aOut*20, aOut*20
endin
</CsInstruments>
<CsScore>
; p1 p2 p3
i 1 0 0.1
i 1 0.1 0.1
i 2 1 1
i 3 2 1
i 4 3 1
i 5 4 1
</CsScore>
</CsoundSynthesizer>
You can think of variables as named connectors between opcodes. You can connect the output from an opcode to the input of another. The type of connector (audio, control, etc.) is determined by the first letter of its name.
For a more detailed discussion, see the article An overview Of Csound Variable Types by Andrés Cabrera in the Csound Journal, and the page about Types, Constants and Variables in the Canonical Csound Manual.
Local Scope
The scope of these variables is usually the instrument in which they are defined. They are local variables. In the following example, the variables in instrument 1 and instrument 2 have the same names, but different values.
EXAMPLE 03B02_Local_scope.csd
<CsoundSynthesizer>
<CsOptions>
-odac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
nchnls = 2
0dbfs = 1
instr 1
;i-variable
iMyVar init 0
iMyVar = iMyVar + 1
print iMyVar
;k-variable
kMyVar init 0
kMyVar = kMyVar + 1
printk 0, kMyVar
;a-variable
aMyVar oscils .2, 400, 0
outs aMyVar, aMyVar
;S-variable updated just at init-time
SMyVar1 sprintf "This string is updated just at init-time:
kMyVar = %d\n", i(kMyVar)
printf "%s", kMyVar, SMyVar1
;S-variable updated at each control-cycle
SMyVar2 sprintfk "This string is updated at k-time:
kMyVar = %d\n", kMyVar
printf "%s", kMyVar, SMyVar2
endin
instr 2
;i-variable
iMyVar init 100
iMyVar = iMyVar + 1
print iMyVar
;k-variable
kMyVar init 100
kMyVar = kMyVar + 1
printk 0, kMyVar
;a-variable
aMyVar oscils .3, 600, 0
outs aMyVar, aMyVar
;S-variable updated just at init-time
SMyVar1 sprintf "This string is updated just at init-time:
kMyVar = %d\n", i(kMyVar)
printf "%s", kMyVar, SMyVar1
;S-variable updated at each control-cycle
SMyVar2 sprintfk "This string is updated at k-time:
kMyVar = %d\n", kMyVar
printf "%s", kMyVar, SMyVar2
endin
</CsInstruments>
<CsScore>
i 1 0 .3
i 2 1 .3
</CsScore>
</CsoundSynthesizer>
This is the output (first the output at init-time by the print opcode, then at each k-cycle the output of printk and the two printf opcodes):
new alloc for instr 1:
instr 1: iMyVar = 1.000
i 1 time 0.10000: 1.00000
This string is updated just at init-time: kMyVar = 0
This string is updated at k-time: kMyVar = 1
i 1 time 0.20000: 2.00000
This string is updated just at init-time: kMyVar = 0
This string is updated at k-time: kMyVar = 2
i 1 time 0.30000: 3.00000
This string is updated just at init-time: kMyVar = 0
This string is updated at k-time: kMyVar = 3
B 0.000 .. 1.000 T 1.000 TT 1.000 M: 0.20000 0.20000
new alloc for instr 2:
instr 2: iMyVar = 101.000
i 2 time 1.10000: 101.00000
This string is updated just at init-time: kMyVar = 100
This string is updated at k-time: kMyVar = 101
i 2 time 1.20000: 102.00000
This string is updated just at init-time: kMyVar = 100
This string is updated at k-time: kMyVar = 102
i 2 time 1.30000: 103.00000
This string is updated just at init-time: kMyVar = 100
This string is updated at k-time: kMyVar = 103
B 1.000 .. 1.300 T 1.300 TT 1.300 M: 0.29998 0.29998
Global Scope
If you need variables which are recognized beyond the scope of an instrument, you must define them as global. This is done by prefixing the character g before the types i, k, a or S. See the following example:
EXAMPLE 03B03_Global_scope.csd
<CsoundSynthesizer>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
nchnls = 2
0dbfs = 1
;global scalar variables should be inititalized in the header
giMyVar init 0
gkMyVar init 0
instr 1
;global i-variable
giMyVar = giMyVar + 1
print giMyVar
;global k-variable
gkMyVar = gkMyVar + 1
printk 0, gkMyVar
;global S-variable updated just at init-time
gSMyVar1 sprintf "This string is updated just at init-time:
gkMyVar = %d\n", i(gkMyVar)
printf "%s", gkMyVar, gSMyVar1
;global S-variable updated at each control-cycle
gSMyVar2 sprintfk "This string is updated at k-time:
gkMyVar = %d\n", gkMyVar
printf "%s", gkMyVar, gSMyVar2
endin
instr 2
;global i-variable, gets value from instr 1
giMyVar = giMyVar + 1
print giMyVar
;global k-variable, gets value from instr 1
gkMyVar = gkMyVar + 1
printk 0, gkMyVar
;global S-variable updated just at init-time, gets value from instr 1
printf "Instr 1 tells: '%s'\n", gkMyVar, gSMyVar1
;global S-variable updated at each control-cycle, gets value from instr 1
printf "Instr 1 tells: '%s'\n\n", gkMyVar, gSMyVar2
endin
</CsInstruments>
<CsScore>
i 1 0 .3
i 2 0 .3
</CsScore>
</CsoundSynthesizer>
The output shows the global scope, as instrument 2 uses the values which have been changed by instrument 1 in the same control cycle:new alloc for instr 1:
instr 1: giMyVar = 1.000
new alloc for instr 2:
instr 2: giMyVar = 2.000
i 1 time 0.10000: 1.00000
This string is updated just at init-time: gkMyVar = 0
This string is updated at k-time: gkMyVar = 1
i 2 time 0.10000: 2.00000
Instr 1 tells: 'This string is updated just at init-time: gkMyVar = 0'
Instr 1 tells: 'This string is updated at k-time: gkMyVar = 1'
i 1 time 0.20000: 3.00000
This string is updated just at init-time: gkMyVar = 0
This string is updated at k-time: gkMyVar = 3
i 2 time 0.20000: 4.00000
Instr 1 tells: 'This string is updated just at init-time: gkMyVar = 0'
Instr 1 tells: 'This string is updated at k-time: gkMyVar = 3'
i 1 time 0.30000: 5.00000
This string is updated just at init-time: gkMyVar = 0
This string is updated at k-time: gkMyVar = 5
i 2 time 0.30000: 6.00000
Instr 1 tells: 'This string is updated just at init-time: gkMyVar = 0'
Instr 1 tells: 'This string is updated at k-time: gkMyVar = 5'
How To Work With Global Audio Variables
Some special considerations must be taken if you work with global audio variables. Actually, Csound behaves basically the same whether you work with a local or a global audio variable. But usually you work with global audio variables if you want to add several audio signals to a global signal, and that makes a difference.
The next few examples are going into a bit more detail. If you just want to see the result (= global audio usually must be cleared), you can skip the next examples and just go to the last one of this section.
It should be understood first that a global audio variable is treated the same by Csound if it is applied like a local audio signal:
EXAMPLE 03B04_Global_audio_intro.csd
<CsoundSynthesizer>
<CsOptions>
-odac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 32
nchnls = 2
0dbfs = 1
instr 1; produces a 400 Hz sine
gaSig oscils .1, 400, 0
endin
instr 2; outputs gaSig
outs gaSig, gaSig
endin
</CsInstruments>
<CsScore>
i 1 0 3
i 2 0 3
</CsScore>
</CsoundSynthesizer>
Of course there is no need to use a global variable in this case. If you do it, you risk your audio will be overwritten by an instrument with a higher number using the same variable name. In the following example, you will just hear a 600 Hz sine tone, because the 400 Hz sine of instrument 1 is overwritten by the 600 Hz sine of instrument 2:
EXAMPLE 03B05_Global_audio_overwritten.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 32
nchnls = 2
0dbfs = 1
instr 1; produces a 400 Hz sine
gaSig oscils .1, 400, 0
endin
instr 2; overwrites gaSig with 600 Hz sine
gaSig oscils .1, 600, 0
endin
instr 3; outputs gaSig
outs gaSig, gaSig
endin
</CsInstruments>
<CsScore>
i 1 0 3
i 2 0 3
i 3 0 3
</CsScore>
</CsoundSynthesizer>
In general, you will use a global audio variable like a bus to which several local audio signal can be added. It's this addition of a global audio signal to its previous state which can cause some trouble. Let's first see a simple example of a control signal to understand what is happening:
EXAMPLE 03B06_Global_audio_added.csd
<CsoundSynthesizer>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
nchnls = 2
0dbfs = 1
instr 1
kSum init 0; sum is zero at init pass
kAdd = 1; control signal to add
kSum = kSum + kAdd; new sum in each k-cycle
printk 0, kSum; print the sum
endin
</CsInstruments>
<CsScore>
i 1 0 1
</CsScore>
</CsoundSynthesizer>
In this case, the "sum bus" kSum increases at each control cycle by 1, because it adds the kAdd signal (which is always 1) in each k-pass to its previous state. It is no different if this is done by a local k-signal, like here, or by a global k-signal, like in the next example:
EXAMPLE 03B07_Global_control_added.csd
<CsoundSynthesizer>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
nchnls = 2
0dbfs = 1
gkSum init 0; sum is zero at init
instr 1
gkAdd = 1; control signal to add
endin
instr 2
gkSum = gkSum + gkAdd; new sum in each k-cycle
printk 0, gkSum; print the sum
endin
</CsInstruments>
<CsScore>
i 1 0 1
i 2 0 1
</CsScore>
</CsoundSynthesizer>
What happens when working with audio signals instead of control signals in this way, repeatedly adding a signal to its previous state? Audio signals in Csound are a collection of numbers (a vector). The size of this vector is given by the ksmps constant. If your sample rate is 44100, and ksmps=100, you will calculate 441 times in one second a vector which consists of 100 numbers, indicating the amplitude of each sample.
So, if you add an audio signal to its previous state, different things can happen, depending on the vector's present and previous states. If both previous and present states (with ksmps=9) are [0 0.1 0.2 0.1 0 -0.1 -0.2 -0.1 0] you will get a signal which is twice as strong: [0 0.2 0.4 0.2 0 -0.2 -0.4 -0.2 0]. But if the present state is opposite [0 -0.1 -0.2 -0.1 0 0.1 0.2 0.1 0], you will only get zeros when you add them. This is shown in the next example with a local audio variable, and then in the following example with a global audio variable.
EXAMPLE 03B08_Local_audio_add.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
;(change to 441 to see the difference)
nchnls = 2
0dbfs = 1
instr 1
;initialize a general audio variable
aSum init 0
;produce a sine signal (change frequency to 401 to see the difference)
aAdd oscils .1, 400, 0
;add it to the general audio (= the previous vector)
aSum = aSum + aAdd
kmax max_k aSum, 1, 1; calculate maximum
printk 0, kmax; print it out
outs aSum, aSum
endin
</CsInstruments>
<CsScore>
i 1 0 1
</CsScore>
</CsoundSynthesizer>
prints:
i 1 time 0.10000: 0.10000
i 1 time 0.20000: 0.20000
i 1 time 0.30000: 0.30000
i 1 time 0.40000: 0.40000
i 1 time 0.50000: 0.50000
i 1 time 0.60000: 0.60000
i 1 time 0.70000: 0.70000
i 1 time 0.80000: 0.79999
i 1 time 0.90000: 0.89999
i 1 time 1.00000: 0.99999
EXAMPLE 03B09_Global_audio_add.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 4410; very high because of printing
;(change to 441 to see the difference)
nchnls = 2
0dbfs = 1
;initialize a general audio variable
gaSum init 0
instr 1
;produce a sine signal (change frequency to 401 to see the difference)
aAdd oscils .1, 400, 0
;add it to the general audio (= the previous vector)
gaSum = gaSum + aAdd
endin
instr 2
kmax max_k gaSum, 1, 1; calculate maximum
printk 0, kmax; print it out
outs gaSum, gaSum
endin
</CsInstruments>
<CsScore>
i 1 0 1
i 2 0 1
</CsScore>
</CsoundSynthesizer>
In both cases, you get a signal which increases each 1/10 second, because you have 10 control cycles per second (ksmps=4410), and the frequency of 400 Hz can be evenly divided by this. If you change the ksmps value to 441, you will get a signal which increases much faster and is out of range after 1/10 second. If you change the frequency to 401 Hz, you will get a signal which increases first, and then decreases, because each audio vector has 40.1 cycles of the sine wave. So the phases are shifting; first getting stronger and then weaker. If you change the frequency to 10 Hz, and then to 15 Hz (at ksmps=44100), you cannot hear anything, but if you render to file, you can see the whole process of either enforcing or erasing quite clear:
Self-reinforcing global audio signal on account of its state in one control cycle being the same as in the previous one
So the result of all is: If you work with global audio variables in a way that you add several local audio signals to a global audio variable (which works like a bus), you must clear this global bus at each control cycle. As in Csound all the instruments are calculated in ascending order, it should be done either at the beginning of the first, or at the end of the last instrument. Perhaps it is the best idea to declare all global audio variables in the orchestra header first, and then clear them in an "always on" instrument with the highest number of all the instruments used. This is an example of a typical situation:
EXAMPLE 03B10_Global_with_clear.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 32
nchnls = 2
0dbfs = 1
;initialize the global audio variables
gaBusL init 0
gaBusR init 0
;make the seed for random values each time different
seed 0
instr 1; produces short signals
loop:
iDur random .3, 1.5
timout 0, iDur, makenote
reinit loop
makenote:
iFreq random 300, 1000
iVol random -12, -3; dB
iPan random 0, 1; random panning for each signal
aSin oscil3 ampdb(iVol), iFreq, 1
aEnv transeg 1, iDur, -10, 0; env in a-rate is cleaner
aAdd = aSin * aEnv
aL, aR pan2 aAdd, iPan
gaBusL = gaBusL + aL; add to the global audio signals
gaBusR = gaBusR + aR
endin
instr 2; produces short filtered noise signals (4 partials)
loop:
iDur random .1, .7
timout 0, iDur, makenote
reinit loop
makenote:
iFreq random 100, 500
iVol random -24, -12; dB
iPan random 0, 1
aNois rand ampdb(iVol)
aFilt reson aNois, iFreq, iFreq/10
aRes balance aFilt, aNois
aEnv transeg 1, iDur, -10, 0
aAdd = aRes * aEnv
aL, aR pan2 aAdd, iPan
gaBusL = gaBusL + aL; add to the global audio signals
gaBusR = gaBusR + aR
endin
instr 3; reverb of gaBus and output
aL, aR freeverb gaBusL, gaBusR, .8, .5
outs aL, aR
endin
instr 100; clear global audios at the end
clear gaBusL, gaBusR
endin
</CsInstruments>
<CsScore>
f 1 0 1024 10 1 .5 .3 .1
i 1 0 20
i 2 0 20
i 3 0 20
i 100 0 20
</CsScore>
</CsoundSynthesizer>
The chn Opcodes For Global Variables
Instead of using the traditional g-variables for any values or signals which are to transfer between several instruments, it is also possible to use the chn opcodes. An i-, k-, a- or S-value or signal can be set by chnset and received by chnget. One advantage is to have strings as names, so that you can choose intuitive names.
For audio variables, instead of performing an addition, you can use the chnmix opcode. For clearing an audio variable, the chnclear opcode can be used.
EXAMPLE 03B11_Chn_demo.csd
<CsoundSynthesizer>
<CsOptions>
-o dac
</CsOptions>
<CsInstruments>
;Example by Joachim Heintz
sr = 44100
ksmps = 32
nchnls = 2
0dbfs = 1
instr 1; send i-values
chnset 1, "sio"
chnset -1, "non"
endin
instr 2; send k-values
kfreq randomi 100, 300, 1
chnset kfreq, "cntrfreq"
kbw = kfreq/10
chnset kbw, "bandw"
endin
instr 3; send a-values
anois rand .1
chnset anois, "noise"
loop:
idur random .3, 1.5
timout 0, idur, do
reinit loop
do:
ifreq random 400, 1200
iamp random .1, .3
asig oscils iamp, ifreq, 0
aenv transeg 1, idur, -10, 0
asine = asig * aenv
chnset asine, "sine"
endin
instr 11; receive some chn values and send again
ival1 chnget "sio"
ival2 chnget "non"
print ival1, ival2
kcntfreq chnget "cntrfreq"
kbandw chnget "bandw"
anoise chnget "noise"
afilt reson anoise, kcntfreq, kbandw
afilt balance afilt, anoise
chnset afilt, "filtered"
endin
instr 12; mix the two audio signals
amix1 chnget "sine"
amix2 chnget "filtered"
chnmix amix1, "mix"
chnmix amix2, "mix"
endin
instr 20; receive and reverb
amix chnget "mix"
aL, aR freeverb amix, amix, .8, .5
outs aL, aR
endin
instr 100; clear
chnclear "mix"
endin
</CsInstruments>
<CsScore>
i 1 0 20
i 2 0 20
i 3 0 20
i 11 0 20
i 12 0 20
i 20 0 20
i 100 0 20
</CsScore>
</CsoundSynthesizer>