#lang racket 
  
(require portaudio) 
  
(define pitch 426) 
(define base-frames 0) 
(define sample-rate 44100.0) 
(define tpisr (* 2 pi (/ 1.0 sample-rate))) 
(define (real->s16 x) 
  (inexact->exact (round (* 32767 x)))) 
  
(define (buffer-filler setter frames) 
  (for ([i (in-range frames)] 
        [f (in-range base-frames (+ base-frames frames))]) 
    (define sample 
      (real->s16 (* 0.2 (sin (* tpisr f pitch))))) 
    (setter (* i 2) sample) 
    (setter (+ 1 (* i 2)) sample)) 
  (set! base-frames (+ base-frames frames))) 
  
(match-define (list timer stats stopper) 
              (stream-play buffer-filler 0.2 sample-rate))