(define (threshold t)
  (cond [(> t 1) 1]
        [(< t -1) -1]
        [else t]))

(define (sinewtf t f)
  (* 0.25 (threshold
  (+ (* 1 (sin (* twopi t f 1/44100)))
     (- 1 (sin (* twopi t 1/44100)))
     (+ 1 (sin (* twopi f 1/44100)))

))))