liveconv
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## liveconv

liveconv — Partitioned convolution with dynamically reloadable impulse response

## Description

Computationally efficient, partitioned convolution, using a function table as impulse response (IR) source, similar to the ftconv opcode. The liveconv opcode allows dynamic reload of IR data at any time while the convolution is running, controlled by the kupdate parameter. Due to the manner in which the IR is updated, the operation can be done without audio artifacts in the convolution output.

The IR table is read partition by partition after signalling an update. The first ksmps samples must be available when the update flag is set. The rest of the table can be continuously filled in consecutive passes. There may be a new update for every partition, allowing as many as ftlen/iplen simultaneous updates (ftlen is the length of the IR table).

The low-latency, dynamic behavior of liveconv makes it ideal for convolution with live sampled impulse responses, and/or real-time impulse response transformations and modifications.

## Syntax

    ares liveconv ain, ift, iplen, kupdate, kclear

## Initialization

ift -- table number for storing the impulse response (IR) for convolution. The table may be filled with new data at any time while the convolution is running.

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

## Performance

ain -- input signal.

ares -- output signal.

kupdate -- flag indicating whether the IR table should be updated. If kupdate=1 the IR table ift is loaded partition by partition, starting with the next partition. If kupdate=-1 the IR table ift is unloaded (cleared to zero) partition by partition, starting with the next partition. Other values have no effect.

kclear -- flag for clearing all internal buffers. If kclear has any value != zero, the internal buffers are cleared immediately. This operation is not free of artifacts.

## Example

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

Example 474. Example of the liveconv opcode.

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

    <CsoundSynthesizer>
    <CsOptions>
    -odac  ;realtime audio out
    </CsOptions>
    <CsInstruments>

    	sr	= 44100
    	nchnls	= 2
    	0dbfs	= 1

    ; empty IR table
    giIR_record 	ftgen	0, 0, 131072, 2, 0

    ; Record impulse response
    instr 13

    p3 		=	ftlen(giIR_record)/sr
    iskip 	=	p4
    irlen 	=	p5
    a1 		diskin2	"fox.wav", 1, iskip

    ; Fill IR table with segment from audio file
    amp 	linseg	0, 0.1, 1, irlen, 1, 0.1, 0, 1, 0
    andx_IR line	0, 1, 1/(ftlen(giIR_record)/sr)
    		tablew	a1*amp, andx_IR, giIR_record, 1
    		outch	1, a1*amp	; output the IR
    ktrig 	init	1
    if ktrig > -1 then
    	chnset	ktrig, "conv_update"
    	ktrig -= 1
    endif

    endin

    ; The convolver
    instr 14

    ain 	diskin2	"beats.wav", 1, 0, 1
    kupdate chnget	"conv_update"
    aconv 	liveconv ain, giIR_record, 2048, kupdate, 0
    		outch	2, aconv*0.009	; output the convolution response
    endin

    </CsInstruments>
    <CsScore>
    ; record impulse response
    ;          skip  IR_dur
    i13	0	1	0.0	0.5
    i13	2	1	0.5	0.5
    i13	4	1	1.0	0.5
    i13	6	1	1.5	0.5
    i13	8	1	2.0	0.75
    i13	10	1	2.38 0.25

    ; convolve
    i14	0.0	11.65

    e

    </CsScore>
    </CsoundSynthesizer>

## See also

ftconv tvconv pconvolve, convolve,

## Credits

Author: Sigurd Saue, Oeyvind Brandtsegg
2017

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