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rfft

Fast Fourier Transform of a real-value array.

Applies a forward Fast Fourier Transform to a real-value input 1-dimensional array. The output is another array containing the transform, non-redundant, non-negative spectrum only. If the input array is power-of-two, the output array size will match the input size, with the first two points containing 0Hz and Nyquist frequency coefficients. Otherwise, the output will have two extra values (input size + 2), and the the Nyquist coefficient will be placed at kin[input_size] position (kin[1] and kin[input_size+1] will be 0).

Syntax

kout[] rfft kin[]

Performance

kout[] -- output array containing the transform. It will be created if it does not exist.

kin[] -- input array containing the real-valued input.

Examples

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

Example of the rfft opcode.
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<CsoundSynthesizer>

<CsOptions>
-d -o dac
</CsOptions>

<CsInstruments>
;ksmps needs to be an integer div of hopsize
ksmps = 64
0dbfs=1

instr 1

 ihopsize = 256   ; hopsize
 ifftsize = 1024  ; FFT size
 iolaps = ifftsize/ihopsize ; overlaps
 ibw = sr/ifftsize ; bin bandwidth
 kcnt init 0    ; counting vars
 krow init 0

 kOla[] init ifftsize ; overlap-add buffer
 kIn[] init ifftsize  ; input buffer
 kSw[] init ifftsize
 kOut[][] init iolaps, ifftsize ; output buffers

 a1 diskin2 "fox.wav",1,0,1 ; audio input
 ks  expon  100, p3, 1000
 asw vco2  0.15, ks

 /* every hopsize samples */
 if kcnt == ihopsize then
   /* window and take FFT */
   kWin[] window kIn,krow*ihopsize
   kSpec[] rfft kWin
   kWin window kSw,krow*ihopsize
   kSpec2[] rfft kWin
   kProd[] cmplxprod kSpec, kSpec2

   /* IFFT + window */
   kRow[] rifft kProd + kSpec
   kWin window kRow, krow*ihopsize
   /* place it on out buffer */
   kOut setrow kWin, krow

   /* zero the ola buffer */
   kOla = 0
   /* overlap-add */
   ki = 0
   until ki == iolaps do
     kRow getrow kOut, ki
     kOla = kOla + kRow
     ki += 1
   od

  /* update counters */
  krow = (krow+1)%iolaps
  kcnt = 0
 endif

 /* shift audio in/out of buffers */
 kIn shiftin a1
 kSw shiftin asw
 a2 shiftout kOla
    out a2/iolaps

 /* increment counter */
 kcnt += ksmps

endin

</CsInstruments>

<CsScore>
i1 0 10
</CsScore>

</CsoundSynthesizer>

See Also

Vectorial opcodes

array opcodes

Array-based spectral opcodes

Credits

Author: Victor Lazzarini
NUI Maynooth
2014

New in version 6.04