#lang scribble/manual
@(require (for-label racket))

@title{(fb-sine-c rate freq im fb a c xi yi)}

Feedback sine with chaotic phase indexing.

freq - iteration frequency in Hz    - 22050
im   - index multiplier amount      - 1
fb   - feedback amount              - 0.1
a    - phase multiplier amount      - 1.1
c    - phase increment amount       - 0.5
xi   - initial value of x           - 0.1
yi   - initial value of y           - 0.1

A cubic-interpolating sound generator based on the difference
equations:

	xn+1 = sin(im*yn + fb*xn)
	yn+1 = (ayn + c) % 2pi

This uses a linear congruential function to drive the phase
indexing of a sine wave.  For im = 1, fb = 0, and a = 1 a normal
sinewave results.

sclang default values

(audition
 (out 0 (mul (fb-sine-c ar (fdiv sample-rate 4) 1 0.1 1.1 0.5 0.1 0.1) 
	     0.2)))

increase feedback

(let ((fb (line kr 0.01 4 10 do-nothing)))
  (audition
   (out 0 (mul (fb-sine-c ar sample-rate 1 fb 1.1 0.5 0.1 0.1) 0.2))))

increase phase multiplier

(let ((a (line kr 1 2 10 do-nothing)))
  (audition
   (out 0 (mul (fb-sine-c ar sample-rate 1 0 a 0.5 0.1 0.1) 0.2))))

randomly modulate parameters

(let* ((x (mouse-x kr 1 12 0 0.1))
       (f (lambda (m a) (mul-add (lf-noise2 kr x) m a))))
  (audition
   (out 0 (mul (fb-sine-c ar
			  (f 1e4 1e4)
			  (f 32 33)
			  (f 0.5 0)
			  (f 0.05 1.05)
			  (f 0.3 0.3)
			  0.1
			  0.1)
	       0.2))))