ftconv
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## ftconv

ftconv — Low latency multichannel convolution, using a function table as impulse response source.

## Description

Low latency multichannel convolution, using a function table as impulse response source. The algorithm is to split the impulse response to partitions of length determined by the 'iplen' parameter, and delay and mix partitions so that the original, full length impulse response is reconstructed without gaps. The output delay (latency) is 'iplen' samples, and does not depend on the control rate, unlike in the case of other convolve opcodes.

## Syntax

    a1[, a2[, a3[, ... a8]]] ftconv ain, ift, iplen[, iskipsamples [, iirlen[, iskipinit]]]

## Initialization

ift -- source ftable number. The table is expected to contain interleaved multichannel audio data, with the number of channels equal to the number of output variables (a1, a2, etc.). An interleaved table can be created from a set of mono tables with GEN52.

iplen -- length of impulse response partitions, in sample frames; must be an integer power of two. Lower settings allow for shorter output delay, but will increase CPU usage.

iskipsamples (optional, defaults to zero) -- number of sample frames to skip at the beginning of the table. Useful for reverb responses that have some amount of initial delay. If this delay is not less than 'iplen' samples, then setting iskipsamples to the same value as iplen will eliminate any additional latency by ftconv.

iirlen (optional) -- total length of impulse response, in sample frames. The default is to use all table data (not including the guard point).

iskipinit (optional, defaults to zero) -- if set to any non-zero value, skip initialization whenever possible without causing an error.

## Performance

ain -- input signal.

a1 ... a8 -- output signal(s).

## Example

    <CsoundSynthesizer>
    <CsInstruments>
    sr      =  48000
    ksmps   =  32
    nchnls  =  2
    0dbfs   =  1

    garvb   init 0
    gaW     init 0
    gaX     init 0
    gaY     init 0

    itmp    ftgen   1, 0, 64, -2, 2, 40, -1, -1, -1, 123,           \
                   1, 13.000, 0.05, 0.85, 20000.0, 0.0, 0.50, 2,   \
                   1,  2.000, 0.05, 0.85, 20000.0, 0.0, 0.25, 2,   \
                   1, 16.000, 0.05, 0.85, 20000.0, 0.0, 0.35, 2,   \
                   1,  9.000, 0.05, 0.85, 20000.0, 0.0, 0.35, 2,   \
                   1, 12.000, 0.05, 0.85, 20000.0, 0.0, 0.35, 2,   \
                   1,  8.000, 0.05, 0.85, 20000.0, 0.0, 0.35, 2

    itmp    ftgen 2, 0, 262144, -2, 0
           spat3dt 2, -0.2, 1, 0, 1, 1, 2, 0.005

    itmp    ftgen 3, 0, 262144, -52, 3, 2, 0, 4, 2, 1, 4, 2, 2, 4

           instr 1

    a1      vco2 1, 440, 10
    kfrq    port 100, 0.008, 20000
    a1      butterlp a1, kfrq
    a2      linseg 0, 0.003, 1, 0.01, 0.7, 0.005, 0, 1, 0
    a1      =  a1 * a2 * 2
           denorm a1
           vincr garvb, a1
    aw, ax, ay, az  spat3di a1, p4, p5, p6, 1, 1, 2
           vincr gaW, aw
           vincr gaX, ax
           vincr gaY, ay

           endin

           instr 2

           denorm garvb
    ; skip as many samples as possible without truncating the IR
    arW, arX, arY   ftconv garvb, 3, 2048, 2048, (65536 - 2048)
    aW      =  gaW + arW
    aX      =  gaX + arX
    aY      =  gaY + arY
    garvb   =  0
    gaW     =  0
    gaX     =  0
    gaY     =  0

    aWre, aWim      hilbert aW
    aXre, aXim      hilbert aX
    aYre, aYim      hilbert aY
    aWXr    =  0.0928*aXre + 0.4699*aWre
    aWXiYr  =  0.2550*aXim - 0.1710*aWim + 0.3277*aYre
    aL      =  aWXr + aWXiYr
    aR      =  aWXr - aWXiYr

           outs aL, aR

           endin

    </CsInstruments>
    <CsScore>

    i 1 0 0.5  0.0  2.0 -0.8
    i 1 1 0.5  1.4  1.4 -0.6
    i 1 2 0.5  2.0  0.0 -0.4
    i 1 3 0.5  1.4 -1.4 -0.2
    i 1 4 0.5  0.0 -2.0  0.0
    i 1 5 0.5 -1.4 -1.4  0.2
    i 1 6 0.5 -2.0  0.0  0.4
    i 1 7 0.5 -1.4  1.4  0.6
    i 1 8 0.5  0.0  2.0  0.8
    i 2 0 10
    e

    </CsScore>
    </CsoundSynthesizer>

## Credits

Author: Istvan Varga
2005

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