alpass
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## alpass

alpass — Reverberates an input signal with a flat frequency response.

## Description

Reverberates an input signal with a flat frequency response.

## Syntax

    ares alpass asig, krvt, ilpt [, iskip] [, insmps]

## Initialization

ilpt -- loop time in seconds, which determines the “echo density” of the reverberation. This in turn characterizes the “color” of the filter whose frequency response curve will contain ilpt * sr/2 peaks spaced evenly between 0 and sr/2 (the Nyquist frequency). Loop time can be as large as available memory will permit. The space required for an n second loop is 4n*sr bytes. The delay space is allocated and returned as in delay.

iskip (optional, default=0) -- initial disposition of delay-loop data space (cf. reson). The default value is 0.

insmps (optional, default=0) -- delay amount, as a number of samples.

## Performance

krvt -- the reverberation time (defined as the time in seconds for a signal to decay to 1/1000, or 60dB down from its original amplitude).

This filter reiterates the input with an echo density determined by loop time ilpt. The attenuation rate is independent and is determined by krvt, the reverberation time (defined as the time in seconds for a signal to decay to 1/1000, or 60dB down from its original amplitude). Output will begin to appear immediately.

## Examples

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

Example 44. Example of the alpass opcode.

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
    -odac     ;;;RT audio out
    ;-iadc    ;;;uncomment -iadc if RT audio input is needed too
    ; For Non-realtime ouput leave only the line below:
    ; -o alpass.wav -W ;;; for file output any platform
    </CsOptions>
    <CsInstruments>

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

    gamix init 0

    instr 1

    kcps    expon p4, p3, p5
    asig	vco2  0.6, kcps
    	outs  asig, asig

    gamix = gamix + asig

    endin

    instr 99

    krvt =  3.5
    ilpt =  0.1
    aleft	alpass gamix, krvt*1.5, ilpt
    aright	alpass gamix, krvt, ilpt*2
    	outs   aleft, aright

    gamix = 0	; clear mixer

    endin

    </CsInstruments>
    <CsScore>

    i 1 0 3 20 2000

    i 99 0 8
    e

    </CsScore>
    </CsoundSynthesizer>

## See Also

comb, reverb, valpass, vcomb

## Credits

Author: William “Pete” Moss (vcomb and valpass)
University of Texas at Austin
Austin, Texas USA
January 2002

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