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rms

Determines the root-mean-square amplitude of an audio signal.

It low-pass filters the actual value, to average in the manner of a VU meter.

Syntax

kres rms asig [, ihp] [, iskip]

Initialization

ihp (optional, default=10) -- half-power point (in Hz) of a special internal low-pass filter. The default value is 10.

iskip (optional, default=0) -- initial disposition of internal data space (see reson). The default value is 0.

Performance

asig -- input audio signal

kres -- low-pass filtered rms value of the input signal

rms output values kres will trace the root-mean-square value of the audio input asig. This unit is not a signal modifier, but functions rather as a signal power-gauge. It uses an internal low-pass filter to make the response smoother. ihp can be used to control this smoothing. The higher the value, the "snappier" the measurement.

This opcode can also be used as an evelope follower.

The kres output from this opcode is given in amplitude and depends on 0dbfs. If you want the output in decibels, you can use dbamp

Examples

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

Example of the rms opcode.
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<CsoundSynthesizer>
<CsOptions>
; 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 rms.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

; By Stefano Cucchi 2020

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

instr 1

areference diskin "fox.wav"
krms rms  areference       ; take the RMS of "fox.wav"
asound oscili krms, 440 ; use RMS as amplitude of sine wave     
outch 1, areference
outch 2, asound
endin


</CsInstruments>
<CsScore>
i 1 0 4
e
</CsScore>
</CsoundSynthesizer>

Here is another example of the rms opcode. It uses the file rms-FLTK.csd.

Advanced example of the rms opcode.
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<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
; Audio out   Audio in    No messages
-odac           -iadc     -d  -m0   ;;;RT audio I/O
; For Non-realtime ouput leave only the line below:
; -o rms.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

; Initialize the global variables.
sr = 44100
ksmps = 128
nchnls = 1

;Example by Andres Cabrera 2007

0dbfs = 1

FLpanel "rms", 400, 100, 50, 50
    gkrmstext, gihrmstext FLtext "Rms", -100, 0, 0.1, 3, 110, 30, 60, 50
    gkihp, gihandle FLtext "ihp", 0, 10, 0.05, 1, 100, 30, 220, 50
    gkrmsslider, gihrmsslider FLslider "", -60, -0.5, -1, 5, -1, 380, 20, 10, 10

FLpanelEnd
FLrun


FLsetVal_i 5, gihandle
; Instrument #1.
instr 1
  a1 inch 1   

label:
  kval rms a1, i(gkihp)  ;measures rms of input channel 1
rireturn

  kval = dbamp(kval) ; convert to db full scale
  printk 0.5, kval
  FLsetVal 1, kval, gihrmsslider   ;update the slider and text values
  FLsetVal 1, kval, gihrmstext
  knewihp changed gkihp   ; reinit when ihp text has changed
  if (knewihp == 1) then
    reinit label  ;needed because ihp is an i-rate parameter
  endif
endin



</CsInstruments>
<CsScore>

; Play Instrument #1 for one minute
i 1 0 60
e


</CsScore>
</CsoundSynthesizer>

See also

Sensing and Control: Envelope followers