WORKING WITH CONTROLLERS
Scanning MIDI Continuous Controllers
The most useful opcode for reading in midi continuous controllers is ctrl7. ctrl7's input arguments allow us to specify midi channel and controller number of the controller to be scanned in addition to giving us the option of rescaling the received midi values between a new minimum and maximum value as defined by the 3rd and 4th input arguments. Further possibilities for modifying the data output are provided by the 5th (optional) argument which is used to point to a function table that reshapes the controller's output response to something possibly other than linear. This can be useful when working with parameters which are normally expressed on a logarithmic scale such as frequency.
The following example scans midi controller 1 on channel 1 and prints values received to the console. The minimum and maximum values are given as 0 and 127 therefore they are not rescaled at all. Controller 1 is also the modulation wheel on a midi keyboard.
EXAMPLE 07C01_ctrl7_print.csd
<CsoundSynthesizer>
<CsOptions>
-Ma -odac
; activate all MIDI devices
</CsOptions>
<CsInstruments>
; 'sr' and 'nchnls' are irrelevant so are omitted
ksmps = 32
instr 1
kCtrl ctrl7 1,1,0,127 ; read in controller 1 on channel 1
kTrigger changed kCtrl ; if 'kCtrl' changes generate a trigger ('bang')
if kTrigger=1 then
; Print kCtrl to console with formatting, but only when its value changes.
printks "Controller Value: %d%n", 0, kCtrl
endif
endin
</CsInstruments>
<CsScore>
i 1 0 3600
e
</CsScore>
<CsoundSynthesizer>
There are also 14 bit and 21 bit versions of ctrl7 (ctrl14 and ctrl21) which improve upon the 7 bit resolution of 'ctrl7' but hardware that outputs 14 or 21 bit controller information is rare so these opcodes are seldom used.
Scanning Pitch Bend and Aftertouch
We can scan pitch bend and aftertouch in a similar way by using the opcodes pchbend and aftouch. Once again we can specify minimum and maximum values with which to rescale the output. In the case of 'pchbend' we specify the value it outputs when the pitch bend wheel is at rest followed by a value which defines the entire range from when it is pulled to its minimum to when it is pushed to its maximum. In this example, playing a key on the keyboard will play a note, the pitch of which can be bent up or down two semitones by using the pitch bend wheel. Aftertouch can be used to modify the amplitude of the note while it is playing. Pitch bend and aftertouch data is also printed at the terminal whenever they change. One thing to bear in mind is that for 'pchbend' to function the Csound instrument that contains it needs to have been activated by a MIDI event, i.e. you will need to play a midi note on your keyboard and then move the pitch bend wheel.
EXAMPLE 07C02_pchbend_aftouch.csd
<CsoundSynthesizer>
<CsOptions>
-odac -Ma
</CsOptions>
<CsInstruments>
sr = 44100
ksmps = 32
nchnls = 1
0dbfs = 1
giSine ftgen 0,0,2^10,10,1 ; a sine wave
instr 1
; -- pitch bend --
kPchBnd pchbend 0,4 ; read in pitch bend (range -2 to 2)
kTrig1 changed kPchBnd ; if 'kPchBnd' changes generate a trigger
if kTrig1=1 then
printks "Pitch Bend:%f%n",0,kPchBnd ; print kPchBnd to console when it changes
endif
; -- aftertouch --
kAfttch aftouch 0,0.9 ; read in aftertouch (range 0 to 0.9)
kTrig2 changed kAfttch ; if 'kAfttch' changes generate a trigger
if kTrig2=1 then
printks "Aftertouch:%d%n",0,kAfttch ; print kAfttch to console when it changes
endif
; -- create a sound --
iNum notnum ; read in MIDI note number
; MIDI note number + pitch bend are converted to cycles per seconds
aSig poscil 0.1,cpsmidinn(iNum+kPchBnd),giSine
out aSig ; audio to output
endin
</CsInstruments>
<CsScore>
f 0 300
e
</CsScore>
<CsoundSynthesizer>
Initialising MIDI Controllers
It may be useful to be able to define the initial value of a midi controller, that is, the value any ctrl7s will adopt until their corresponding hardware controls have been moved. Midi hardware controls only send messages when they change so until this happens their values in Csound defaults to their minimum settings unless additional initialisation has been carried out. As an example, if we imagine we have a Csound instrument in which the output volume is controlled by a midi controller it might prove to be slightly frustrating that each time the orchestra is launched, this instrument will remain silent until the volume control is moved. This frustration might become greater when many midi controllers are begin utilised. It would be more useful to be able to define the starting value for each of these controllers. The initc7 opcode allows us to do this. If initc7 is placed within the instrument itself it will be reinitialised each time the instrument is called, if it is placed in instrument 0 (just after the header statements) then it will only be initialised when the orchestra is first launched. The latter case is probably most useful.
In the following example a simple synthesizer is created. Midi controller 1 controls the output volume of this instrument but the initc7 statement near the top of the orchestra ensures that this control does not default to its minimum setting. The arguments that initc7 takes are for midi channel, controller number and initial value. Initial value is defined within the range 0-1, therefore a value of 1 will set this controller to its maximum value (midi value 127), and a value of 0.5 will set it to its halfway value (midi value 64), and so on.
Additionally this example uses the cpsmidi opcode to scan midi pitch (basically converting midi note numbers to cycles-per-second) and the ampmidi opcode to scan and rescale key velocity.
EXAMPLE 07C03_cpsmidi_ampmidi.csd
<CsoundSynthesizer>
<CsOptions>
-Ma -odac
; activate all midi inputs and real-time audio output
</CsOptions>
<CsInstruments>
; Example by Iain McCurdy
sr = 44100
ksmps = 32
nchnls = 1
0dbfs = 1
giSine ftgen 0,0,2^12,10,1 ; a sine wave
initc7 1,1,1 ; initialize CC 1 on chan. 1 to its max level
instr 1
iCps cpsmidi ; read in midi pitch in cycles-per-second
iAmp ampmidi 1 ; read in key velocity. Rescale to be from 0 to 1
kVol ctrl7 1,1,0,1 ; read in CC 1, chan 1. Rescale to be from 0 to 1
aSig poscil iAmp*kVol, iCps, giSine ; an audio oscillator
out aSig ; send audio to output
endin
</CsInstruments>
<CsScore>
f 0 3600
e
</CsScore>
<CsoundSynthesizer>
You will maybe hear that this instrument produces 'clicks' as notes begin and end. To find out how to prevent this see the section on envelopes with release sensing in the chapter Sound Modification: Envelopes.
Smoothing 7-bit Quantisation in MIDI Controllers
A problem we encounter with 7 bit midi controllers is the poor resolution that they offer us. 7 bit means that we have 2 to the power of 7 possible values; therefore 128 possible values, which is rather inadequate for defining, for example, the frequency of an oscillator over a number of octaves, the cutoff frequency of a filter or a quickly moving volume control. We soon become aware of the parameter that is being changed moving in steps - so not really a 'continuous' controller. We may also experience clicking artefacts, sometimes called 'zipper noise', as the value changes. The extent of this will depend upon the parameter being controlled. There are some things we can do to address this problem. We can filter the controller signal within Csound so that the sudden changes that occur between steps along the controller's travel are smoothed using additional interpolating values - we must be careful not to smooth excessively otherwise the response of the controller will become sluggish. Any k-rate compatible lowpass filter can be used for this task but the portk opcode is particularly useful as it allows us to define the amount of smoothing as a time taken to glide to half the required value rather than having to specify a cutoff frequency. Additionally this 'half time' value can be varied at k-rate which provides an advantage availed of in the following example.
This example takes the simple synthesizer of the previous example as its starting point. The volume control, which is controlled by midi controller 1 on channel 1, is passed through a 'portk' filter. The 'half time' for 'portk' ramps quickly up to its required value of 0.01 through the use of a linseg statement in the previous line. This ensures that when a new note begins the volume control immediately jumps to its required value rather than gliding up from zero as would otherwise be affected by the 'portk' filter. Try this example with the 'portk' half time defined as a constant to hear the difference. To further smooth the volume control, it is converted to an a-rate variable through the use of the interp opcode which, as well as performing this conversion, interpolates values in the gaps between k-cycles.
EXAMPLE 07C04_smoothing.csd
<CsoundSynthesizer>
<CsOptions>
-Ma -odac
</CsOptions>
<CsInstruments>
;Example by Iain McCurdy
sr = 44100
ksmps = 32
nchnls = 1
0dbfs = 1
giSine ftgen 0,0,2^12,10,1
initc7 1,1,1 ; initialize CC 1 to its max. level
instr 1
iCps cpsmidi ; read in midi pitch in cycles-per-second
iAmp ampmidi 1 ; read in note velocity - re-range 0 to 1
kVol ctrl7 1,1,0,1 ; read in CC 1, chan. 1. Re-range from 0 to 1
kPortTime linseg 0,0.001,0.01 ; create a value that quickly ramps up to 0.01
kVol portk kVol,kPortTime ; create a filtered version of kVol
aVol interp kVol ; create an a-rate version of kVol
aSig poscil iAmp*aVol,iCps,giSine
out aSig
endin
</CsInstruments>
<CsScore>
f 0 300
e
</CsScore>
<CsoundSynthesizer>
All of the techniques introduced in this section are combined in the final example which includes a 2-semitone pitch bend and tone control which is controlled by aftertouch. For tone generation this example uses the gbuzz opcode.
EXAMPLE 07C05_MidiControlComplex.csd
<CsoundSynthesizer>
<CsOptions>
-Ma -odac
</CsOptions>
<CsInstruments>
;Example by Iain McCurdy
sr = 44100
ksmps = 32
nchnls = 1
0dbfs = 1
giCos ftgen 0,0,2^12,11,1 ; a cosine wave
initc7 1,1,1 ; initialize controller to its maximum level
instr 1
iNum notnum ; read in midi note number
iAmp ampmidi 0.1 ; read in note velocity - range 0 to 0.2
kVol ctrl7 1,1,0,1 ; read in CC 1, chan. 1. Re-range from 0 to 1
kPortTime linseg 0,0.001,0.01 ; create a value that quickly ramps up to 0.01
kVol portk kVol, kPortTime ; create filtered version of kVol
aVol interp kVol ; create an a-rate version of kVol.
iRange = 2 ; pitch bend range in semitones
iMin = 0 ; equilibrium position
kPchBnd pchbend iMin, 2*iRange ; pitch bend in semitones (range -2 to 2)
kPchBnd portk kPchBnd,kPortTime; create a filtered version of kPchBnd
aEnv linsegr 0,0.005,1,0.1,0 ; amplitude envelope with release stage
kMul aftouch 0.4,0.85 ; read in aftertouch
kMul portk kMul,kPortTime ; create a filtered version of kMul
; create an audio signal using the 'gbuzz' additive synthesis opcode
aSig gbuzz iAmp*aVol*aEnv,cpsmidinn(iNum+kPchBnd),70,0,kMul,giCos
out aSig ; audio to output
endin
</CsInstruments>
<CsScore>
f 0 300
e
</CsScore>
<CsoundSynthesizer>