dam
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## dam

dam — A dynamic compressor/expander.

## Description

This opcode dynamically modifies a gain value applied to the input sound ain by comparing its power level to a given threshold level. The signal will be compressed/expanded with different factors regarding that it is over or under the threshold.

## Syntax

    ares dam asig, kthreshold, icomp1, icomp2, irtime, iftime

## Initialization

icomp1 -- compression ratio for upper zone.

icomp2 -- compression ratio for lower zone

irtime -- gain rise time in seconds. Time over which the gain factor is allowed to raise of one unit.

iftime -- gain fall time in seconds. Time over which the gain factor is allowed to decrease of one unit.

## Performance

asig -- input signal to be modified

kthreshold -- level of input signal which acts as the threshold. Can be changed at k-time (e.g. for ducking)

Note on the compression factors: A compression ratio of one leaves the sound unchanged. Setting the ratio to a value smaller than one will compress the signal (reduce its volume) while setting the ratio to a value greater than one will expand the signal (augment its volume).

## Examples

Because the results of the dam opcode can be subtle, I recommend looking at them in a graphical audio editor program like audacity. audacity is available for Linux, Windows, and the MacOS and may be downloaded from http://audacity.sourceforge.net.

Here is an example of the dam opcode. It uses the file dam.csd, and beats.wav.

Example 93. An example of the dam opcode compressing an audio signal.

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

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

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

    ; Instrument #1, uncompressed signal.
    instr 1
      ; Use the "beats.wav" audio file.
      asig soundin "beats.wav"

      out asig
    endin

    ; Instrument #2, compressed signal.
    instr 2
      ; Use the "beats.wav" audio file.
      asig soundin "beats.wav"

      ; Compress the audio signal.
      kthreshold = 25000
      icomp1 = 0.5
      icomp2 = 0.763
      irtime = 0.1
      iftime = 0.1
      a1 dam asig, kthreshold, icomp1, icomp2, irtime, iftime

      out a1
    endin

    ; Instrument #3, compressed signal.
    instr 3
      ; Use the "beats.wav" audio file.
      asig soundin "beats.wav"

      ; Compress the audio signal.
      kthreshold line 25000, p3, 4410000
      icomp1 = 0.5
      icomp2 = 0.763
      irtime = 0.1
      iftime = 0.1
      a1 dam asig, kthreshold, icomp1, icomp2, irtime, iftime

      out a1
    endin

    </CsInstruments>
    <CsScore>

    ; Play Instrument #1 for 2 seconds.
    i 1 0 2
    ; Play Instrument #2 for 2 seconds.
    i 2 2 2
    ; Play Instrument #3 for 2 seconds.
    i 3 4 2
    e

    </CsScore>
    </CsoundSynthesizer>

This example compresses the audio file “beats.wav”. You should hear a drum pattern repeat twice. The second time, the sound should be quieter (compressed) than the first.

Here is another example of the dam opcode. It uses the file dam_expanded.csd, and mary.wav.

Example 94. An example of the dam opcode expanding an audio signal.

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

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

    ; Instrument #1, normal audio signal.
    instr 1
      ; Use the "mary.wav" audio file.
      asig soundin "mary.wav"

      out asig
    endin

    ; Instrument #2, expanded audio signal.
    instr 2
      ; Use the "mary.wav" audio file.
      asig soundin "mary.wav"

      ; Expand the audio signal.
      kthreshold init 7500
      icomp1 = 2.25
      icomp2 = 2.25
      irtime = 0.1
      iftime = 0.6
      a1 dam asig, kthreshold, icomp1, icomp2, irtime, iftime

      out a1
    endin

    </CsInstruments>
    <CsScore>

    ; Play Instrument #1.
    i 1 0.0 3.5
    ; Play Instrument #2.
    i 2 3.5 3.5
    e

    </CsScore>
    </CsoundSynthesizer>

This example expands the audio file “mary.wav”. You should hear a melody repeat twice. The second time, the sound should be louder (expanded) than the first.

## Credits

Author: Marc Resibois
Belgium
1997

Examples written by Kevin Conder.

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