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

@title{(pitch in initFreq minFreq maxFreq execFreq maxBinsPerOctave}

       median ampThreshold peakThreshold downSample)

Autocorrelation pitch follower

This is a better pitch follower than zero-crossing, but more costly
of CPU. For most purposes the default settings can be used and only
in needs to be supplied. pitch returns two values (via an Array of
outputProxys, see the outputProxy help file), a freq which is the
pitch estimate and hasFreq, which tells whether a pitch was
found. Some vowels are still problematic, for instance a wide open
mouth sound somewhere between a low pitched short 'a' sound as in
'sat', and long 'i' sound as in 'fire', contains enough overtone
energy to confuse the algorithm.

sclang default argument values are: in = 0.0, initFreq = 440.0,
minFreq = 60.0, maxFreq = 4000.0, execFreq = 100.0,
maxBinsPerOctave = 16, median = 1, ampThreshold = 0.01,
peakThreshold = 0.5, downSample = 1.


@racketblock[
(define (pitch* in median ampThreshold)
  (pitch in 444.0 60.0 4000.0 100.0 16 median ampThreshold 0.5 1))
]


@racketblock[
(let* ((in (mul (sin-osc ar (mouse-x kr 220 660 0 0.1) 0) 
		(mouse-y kr 0.05 0.25 0 0.1)))
       (amp (amplitude kr in 0.05 0.05))
       (freq+ (pitch* in 7 0.02))
       (f (fdiv (car (mce-channels freq+)) 2))
       (o (mul (sin-osc ar f 0) amp)))
  (audition (out 0 (mce2 in o))))
]


@racketblock[
(let* ((in (sound-in 0))
       (amp (amplitude kr in 0.05 0.05))
       (freq+ (pitch* in 7 0.02))
       (f (car (mce-channels freq+)))
       (o (mul (sin-osc ar f 0) amp)))
  (audition (out 0 (mce2 in o))))
]