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


insnum -- instrument number

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:

  can't 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 doesn't 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 92. 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
; Audio out   Audio in
-odac           -iadc    ;;;RT audio I/O
; For Non-realtime ouput leave only the line below:
; -o cpuprc.wav -W ;;; for file output any platform

; Initialize the global variables.
sr = 44100
kr = 4410
ksmps = 10
nchnls = 1

; Limit Instrument #1 to 5% of the CPU processing time.
cpuprc 1, 5
; Instrument #1
instr 1
  a1 oscil 10000, 440, 1
  out a1


; Just generate a nice, ordinary sine wave.
f 1 0 32768 10 1

; Play Instrument #1 for one second.
i 1 0 1


See Also

maxalloc, prealloc


Author: Gabriel Maldonado
July, 1999

Example written by Kevin Conder.

New in Csound version 3.57