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# envlpx

envlpx -- Applies an envelope consisting of 3 segments.

## Description

envlpx -- apply an envelope consisting of 3 segments:

1. stored function rise shape

2. modified exponential pseudo steady state

3. exponential decay

## Syntax

ar envlpx xamp, irise, idur, idec, ifn, iatss, iatdec [, ixmod]

kr envlpx kamp, irise, idur, idec, ifn, iatss, iatdec [, ixmod]

## Initialization

irise -- rise time in seconds. A zero or negative value signifies no rise modification.

idur -- overall duration in seconds. A zero or negative value will cause initialization to be skipped.

idec -- decay time in seconds. Zero means no decay. An idec > idur will cause a truncated decay.

ifn -- function table number of stored rise shape with extended guard point.

iatss -- attenuation factor, by which the last value of the envlpx rise is modified during the note's pseudo steady state. A factor greater than 1 causes an exponential growth and a factor less than 1 creates an exponential decay. A factor of 1 will maintain a true steady state at the last rise value. Note that this attenuation is not by fixed rate (as in a piano), but is sensitive to a note's duration. However, if iatss is negative (or if steady state < 4 k-periods) a fixed attenuation rate of abs(iatss) per second will be used. 0 is illegal.

iatdec -- attenuation factor by which the closing steady state value is reduced exponentially over the decay period. This value must be positive and is normally of the order of .01. A large or excessively small value is apt to produce a cutoff which is audible. A zero or negative value is illegal.

ixmod (optional, between +- .9 or so) -- exponential curve modifier, influencing the steepness of the exponential trajectory during the steady state. Values less than zero will cause an accelerated growth or decay towards the target (e.g. subito piano). Values greater than zero will cause a retarded growth or decay. The default value is zero (unmodified exponential).

## Performance

kamp, xamp -- input amplitude signal.

Rise modifications are applied for the first irise seconds, and decay from time idur - idec. If these periods are separated in time there will be a steady state during which amp will be modified by the first exponential pattern. If the rise and decay periods overlap then that will cause a truncated decay. If the overall duration idur is exceeded in performance, the final decay will continue on in the same direction, tending asymptotically to zero.

## Examples

Here is an example of the envlpx opcode. It uses the files envlpx.orc and envlpx.sco.

Example 1. Example of the envlpx opcode.

    /* envlpx.orc */
    ; Initialize the global variables.
    sr = 44100
    kr = 4410
    ksmps = 10
    nchnls = 1

    ; Instrument #1 - a simple instrument.
    instr 1
      ; Set the amplitude.
      kamp init 20000
      ; Get the frequency from the fourth p-field.
      kcps = cpspch(p4)

      a1 vco kamp, kcps, 1
      out a1
    endin

    ; Instrument #2 - instrument with an amplitude envelope.
    instr 2
      kamp = 20000
      irise = 0.05
      idur = p3 - .01
      idec = 0.5
      ifn = 2
      iatss = 1
      iatdec = 0.01

      ; Create an amplitude envelope.
      kenv envlpx kamp, irise, idur, idec, ifn, iatss, iatdec

      ; Get the frequency from the fourth p-field.
      kcps = cpspch(p4)

      a1 vco kenv, kcps, 1
      out a1
    endin
    /* envlpx.orc */

    /* envlpx.sco */
    ; Table #1, a sine wave.
    f 1 0 16384 10 1
    ; Table #2, a rising envelope.
    f 2 0 129 -7 0 128 1

    ; Set the tempo to 120 beats per minute.
    t 0 120

    ; Make sure the score plays for 33 seconds.
    f 0 33

    ; Play a melody with Instrument #1.
    ; p4 = frequency in pitch-class notation.
    i  1  0   1  8.04
    i  1  1   1  8.04
    i  1  2   1  8.05
    i  1  3   1  8.07
    i  1  4   1  8.07
    i  1  5   1  8.05
    i  1  6   1  8.04
    i  1  7   1  8.02
    i  1  8   1  8.00
    i  1  9   1  8.00
    i  1  10  1  8.02
    i  1  11  1  8.04
    i  1  12  2  8.04
    i  1  14  2  8.02

    ; Repeat the melody with Instrument #2.
    ; p4 = frequency in pitch-class notation.
    i  2  16  1  8.04
    i  2  17  1  8.04
    i  2  18  1  8.05
    i  2  19  1  8.07
    i  2  20  1  8.07
    i  2  21  1  8.05
    i  2  22  1  8.04
    i  2  23  1  8.02
    i  2  24  1  8.00
    i  2  25  1  8.00
    i  2  26  1  8.02
    i  2  27  1  8.04
    i  2  28  2  8.04
    i  2  30  2  8.02
    e
    /* envlpx.sco */

## See Also

envlpxr, linen, linenr

## Credits

Thanks goes to Luis Jure for pointing out a mistake with iatss.

Example written by Kevin Conder.

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