Description

Maps elements from a vector onto another according to the indexes of a this vector.

Syntax

vmap  ifn1, ifn2, ielements [,idstoffset, isrcoffset]

Initialization

ifn1 - number of the table where the vectorial signal will be copied, and which contains the mapping vector

ifn2 - number of the table hosting the vectorial signal to be copied

ielements - number of elements to process

idstoffset - index offset for destination table (ifn1)

isrcoffset - index offset for source table (ifn2)

Performance

vmap maps elements of ifn2 according to the values of table ifn1. Elements of ifn1 are treated as indexes of table ifn2, so element values of ifn1 must not exceed the length of ifn2 table otherwise a Csound will report an error. Elements of ifn1 are treated as integers, so any fractional part will be truncated. There is no interpolation performed on this operation.

In practice, what happens is that the elements of ifn1 are used as indexes to ifn2, and then are replaced by the corresponding elements from ifn2. ifn1 must be different from ifn2, otherwise the results are unpredictable. Csound will produce an init error if they are not.

All these operators (vaddv, vsubv, vmultv, vdivv, vpowv, vexpv, vcopy and vmap) are designed to be used together with other opcodes that operate with vectorial signals such as, vcella, adsynt, adsynt2, etc.

Examples

Here is an example of the vmap opcode. Play vmap.csd

<CsoundSynthesizer>

<CsOptions>
; Select audio/midi flags here according to platform
; Audio out   Audio in
-odac           -iadc     ;;;RT audio I/O
; For Non-realtime ouput leave only the line below:
; -o vmap.wav -W ;;; for file output any platform
</CsOptions>

<CsInstruments>
ksmps = 256
nchnls = 2
gisize = 64

gitable ftgen 0, 0, gisize, 10, 1  ;Table to be processed
gimap1 ftgen  0, 0, gisize, -7, gisize-1, gisize-1, 0 ; Mapping function to reverse table
gimap2 ftgen 0, 0, gisize, -5, 1, gisize-1, gisize-1  ; Mapping function for PWM
gimap3 ftgen 0, 0, gisize, -7, 1, (gisize/2)-1, gisize-1, 1, 1, (gisize/2)-1, gisize-1  ; Double frequency

instr 1  ;Hear an oscillator using gitable
asig oscil 10000, 440, gitable
outs asig,asig
endin

instr 2  ;Reverse the table (no sound change, except for a single click
vmap gimap1, gitable, gisize
vcopy_i gitable, gimap1, gisize
turnoff
endin

instr 3  ;Non-interpolated PWM (or phase waveshaping)
vmap gimap2, gitable, gisize
vcopy_i gitable, gimap2, gisize
turnoff
endin

instr 4  ;Double frequency
vmap gimap3, gitable, gisize
vcopy_i gitable, gimap3, gisize
turnoff
endin


</CsInstruments>

<CsScore>
i 1 0 8

i 2 2 1
i 3 4 1
i 4 6 1

e
</CsScore>

</CsoundSynthesizer>

Credits

Written by Gabriel Maldonado.

New in Csound 5 (Previously available only on CsoundAV)