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polynomial

Efficiently evaluates a polynomial of arbitrary order.

The polynomial opcode calculates a polynomial with a single a-rate input variable. The polynomial is a sum of any number of terms in the form kn*x^n where kn is the nth coefficient of the expression. These coefficients are k-rate values.

Syntax

aout polynomial ain, k0 [, k1 [, k2 [...]]]

Performance

ain -- the input signal used as the independent variable of the polynomial ("x").

aout -- the output signal ("y").

k0, k1, k2, ... -- the coefficients for each term of the polynomial.

If we consider the input parameter ain to be "x" and the output aout to be "y", then the polynomial opcode calculates the following equation:

y = k0 + k1*x + k2*x^2 + k3*x^3 + ...

Examples

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

Example of the polynomial opcode.
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<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac  ;;;realtime audio
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o polynomial.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

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

; The polynomial y=x^n where n is odd always produces a curve
; that traverses the range [-1, 1] when the input is within
; the same range.  Therefore, we can use one of these curves
; to make a nonlinear phasor that repeatedly reads a table 
; from beginning to end like a linear phasor (maintaining 
; continuity) but that distorts the waveform in the table.

instr 4 ; This instrument demonstrates phase distortion with x^3

idur   = p3
iamp   = p4
ifreq  = p5
itable = p6

aenv linseg 0, .001, 1.0, idur - .051, 1.0, .05, 0      ; declicking envelope
aosc phasor ifreq                                       ; create a linear phasor
apd  polynomial aosc, 0, 0, 0, 1                        ; distort the phasor with x^3
aout tablei apd, itable, 1                              ; read a sine table with the nonlinear phasor
     outs aenv*aout*iamp, aenv*aout*iamp

endin

instr 5 ; This instrument demonstrates phase distortion with x^11

idur   = p3
iamp   = p4
ifreq  = p5
itable = p6

aenv linseg 0, .001, 1.0, idur - .051, 1.0, .05, 0      ; declicking envelope
aosc phasor ifreq                                       ; create a linear phasor
apd  polynomial aosc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 ; distort the phasor with x^11
aout tablei apd, itable, 1                              ; read a sine table with the nonlinear phasor
     outs aenv*aout*iamp, aenv*aout*iamp

endin

instr 6 ; This instrument crossfades between a pure sine and one distorted with x^11

idur   = p3
iamp   = p4
ifreq  = p5
itable = p6

aenv    linseg  0, .001, 1.0, idur - .051, 1.0, .05, 0  ; declicking envelope
aosc    phasor  ifreq                                   ; create a linear phasor
aout3   tablei  aosc, itable, 1                         ; read a sine table without the linear phasor
apd11   polynomial aosc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 ; distort the phasor with x^11
aout11  tablei  apd11, itable, 1                        ; read a sine table with the nonlinear phasor
kamount linseg  1.0, 0.05, 0.9, 1.0, 0.0                ; crossfade between two outputs
aout    = aout3*kamount + aout11*(1.0 - kamount)
        outs aenv*aout*iamp, aenv*aout*iamp     

endin
</CsInstruments>
<CsScore>
f1 0 16385 10 1 ; sine wave

; descending "just blues" scale

t 0 100
i4 0 .333 .7 512     1
i. + .    .  448
i. + .    .  384
i. + .    .  360
i. + .    .  341.33
i. + .    .  298.67
i. + 2    .  256
s

t 0 100
i5 0 .333 .7 512     1
i. + .    .  448
i. + .    .  384
i. + .    .  360
i. + .    .  341.33
i. + .    .  298.67
i. + 2    .  256
s

t 0 100
i6 0 .333 .7 512     1
i. + .    .  448
i. + .    .  384
i. + .    .  360
i. + .    .  341.33
i. + .    .  298.67
i. + 2    .  256

e

</CsScore>
</CsoundSynthesizer>

See also

Waveshaping

Opcode Equivalents of Functions

Credits

Author: Anthony Kozar
January 2008

New in Csound version 5.08