cpuprc — Control allocation of cpu resources on a per-instrument basis, to optimize realtime output.


Control allocation of cpu resources on a per-instrument basis, to optimize realtime output.


cpuprc insnum, ipercent
cpuprc Sinsname, ipercent


insnum -- instrument number or string

Sinsname -- instrument number or string

ipercent -- percent of cpu processing-time to assign. Can also be expressed as a fractional value.


cpuprc sets the cpu processing-time percent usage of an instrument, in order to avoid buffer underrun in realtime performances, enabling a sort of polyphony theshold. The user must set ipercent value for each instrument to be activated in realtime. Assuming that the total theoretical processing time of the cpu of the computer is 100%, this percent value can only be defined empirically, because there are too many factors that contribute to limiting realtime polyphony in different computers.

For example, if ipercent is set to 5% for instrument 1, the maximum number of voices that can be allocated in realtime, is 20 (5% * 20 = 100%). If the user attempts to play a further note while the 20 previous notes are still playing, Csound inhibits the allocation of that note and will display the following warning message:

  cannot allocate last note because it exceeds 100% of cpu time

In order to avoid audio buffer underruns, it is suggested to set the maximum number of voices slightly lower than the real processing power of the computer. Sometimes an instrument can require more processing time than normal. If, for example, the instrument contains an oscillator which reads a table that does not fit in cache memory, it will be slower than normal. In addition, any program running concurrently in multitasking, can subtract processing power to varying degrees.

At the start, all instruments are set to a default value of ipercent = 0.0% (i.e. zero processing time or rather infinite cpu processing-speed). This setting is OK for deferred-time sessions.

All instances of cpuprc must be defined in the header section, not in the instrument body.


Here is an example of the cpuprc opcode. It uses the file cpuprc.csd.

Example 189. Example of the cpuprc opcode.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

; Select audio/midi flags here according to platform
-odac     ;;;realtime audio out
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o cpuprc.wav -W ;;; for file output any platform

sr = 44100
ksmps = 32
nchnls = 2
0dbfs  = 1

cpuprc 1, 2
cpuprc 2, 30

instr 1 ;cpu processing-time percent usage is set to 2% for each note

asig oscil 0.2, 440, 1
     outs asig, asig

instr 2	;cpu processing-time percent usage is set to 30% for each note
	;so the 4 notes of the score exceeds 100% by far
asig oscil 0.2, 440, 1
     outs asig, asig

f 1 0 32768 10 1	; sine wave

i 1 0 1
i 1 0 1
i 1 0 1
i 1 0 1

;too many notes to process,
;check Csound output!
i 2 3 1
i 2 3 1
i 2 3 1
i 2 3 1

See also

Real-time Performance Control


Author: Gabriel Maldonado
July, 1999

New in Csound version 3.57; named instruments added version 5.13