Csound provides a variety of opcodes, such as cpsmidi, ampmidi and ctrl7, which facilitate the reading of incoming midi data into Csound with minimal fuss. These opcodes allow us to read in midi information without us having to worry about parsing status bytes and so on. Occasionally though when more complex midi interaction is required, it might be advantageous for us to scan all raw midi information that is coming into Csound. The midiin opcode allows us to do this.
In the next example a simple midi monitor is constructed. Incoming midi events are printed to the terminal with some formatting to make them readable. We can disable Csound's default instrument triggering mechanism (which in this example we don't want to use) by writing the line:
massign 0,0
just after the header statement (sometimes referred to as instrument 0).
For this example to work you will need to ensure that you have activated live midi input within Csound, either by using the -M flag or from within the QuteCsound configuration menu. You will also need to make sure that you have a midi keyboard or controller connected. You may also want to include the -m0 flag which will disable some of Csound's additional messaging output and therefore allow our midi printout to be presented more clearly.
The status byte tells us what sort of midi information has been received. For example, a value of 144 tells us that a midi note event has been received, a value of 176 tells us that a midi controller event has been received, a value of 224 tells us that pitch bend has been received and so on.
The meaning of the two data bytes depends on what sort of status byte has been received. For example if a midi note event has been received then data byte 1 gives us the note velocity and data byte 2 gives us the note number. If a midi controller event has been received then data byte 1 gives us the controller number and data byte 2 gives us the controller value.
EXAMPLE 07A01_midiin_print.csd
<CsoundSynthesizer>
<CsOptions>
-Ma -m0
; activates all midi devices, suppress note printings
</CsOptions>
<CsInstruments>
; Example by Iain McCurdy
; no audio so 'sr' or 'nchnls' aren't relevant
ksmps = 32
; using massign with these arguments disables default instrument triggering
massign 0,0
instr 1
kstatus, kchan, kdata1, kdata2 midiin ;read in midi
ktrigger changed kstatus, kchan, kdata1, kdata2 ;trigger if midi data changes
if ktrigger=1 && kstatus!=0 then ;if status byte is non-zero...
; -- print midi data to the terminal with formatting --
printks "status:%d%tchannel:%d%tdata1:%d%tdata2:%d%n"\
,0,kstatus,kchan,kdata1,kdata2
endif
endin
</CsInstruments>
<CsScore>
i 1 0 3600 ; instr 1 plays for 1 hour
</CsScore>
</CsoundSynthesizer>
The principle advantage of using the midiin opcode is that, unlike opcodes such as cpsmidi, ampmidi and ctrl7 which only receive specific midi data types on a specific channel, midiin 'listens' to all incoming data including system exclusive messages. In situations where elaborate Csound instrument triggering mappings that are beyond the capabilities of the default triggering mechanism are required, then the use of midiin might be beneficial.
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