Re: [CM] generators

[bil]

The fm part is normally imitating fm in an oscil.  If you have

(with-sound (:play #t)
  (let ((gen (make-oscil 300)))
 (do ((i 0 (+ i 1)))
 ((= i 2))
   (outa i (* .5 (oscil gen .01))

the .01 fm is just a constant added to the phase-increment which
changes the (constant) frequency of the oscil.  The same thing in nxycos
makes the n cosines jump out (if they were fusing before) mostly
because you've raised the pitch.

Here is fm in nxycos:

(with-sound (:play #t)
  (let ((gen (make-nxycos 300 1/3 3))
(fm (make-oscil 300)))
 (do ((i 0 (+ i 1)))
 ((= i 2))
   (outa i (* .5 (nxycos gen (* .01 (oscil fm


(+ angle fm frequency) is just like (+ 1 2 3).

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[CM] generators

[James Hearon]

Hi,
I've been using the generators in generators.scm for a while, and enjoy making 
sound with them, but for the life of me I cannot seem to understand how they 
work.  I'm confused about the lambda part and the use of fm.  What is fm doing? 
 I'd be grateful if someone could explain that.

Such as in nxycos, It seems like (set! angle (+ angle fm frequency)) is 
critical, but is (+ angle fm frequency), simply the sum of those variables, 
such as (+  3 1 2), > 6? Or does the fm part contribute to the radians value of 
angle in some other way in that bit of code.  I've tried using display and 
formatted output to look at output values such as x, y, den, angle in radians 
in lambda, but nothing is really making sense to me yet.  I've also 
experimented with input of different values and viewing the fft outputs to see 
the frequency in hz, ratio, n, and also angle or phase start in the waveform 
view of snd.

For ex. if I do something like:
 ...
   (outa i (* .5 (nxycos gen 0.1))
such as adding a value for fm, then the frequency really takes off, so I'm not 
sure I'm understanding what fm does in the generator or how it's supposed to be 
used.

Thank you,
Jim



(defgenerator (nxycos :make-wrapper convert-frequency)

  (frequency 0.0) (ratio 1.0) (n 1) (angle 0.0) fm)


(define nxycos


  (let ((+documentation+ "(make-nxycos frequency (ratio 1.0) (n 1)) creates an 
nxycos generator. (nxycos gen (fm 0.0))

returns n cosines from frequency spaced by frequency * ratio."))


(lambda* (gen (fm 0.0))

  (let-set! gen 'fm fm)

  (with-let gen

(let* ((x angle)

  (y (* x ratio))

  (den (sin (* y 0.5

  (set! angle (+ angle fm frequency))

  (if (< (abs den) nearly-zero)

  1.0

  (/ (* (cos (+ x (* 0.5 (- n 1) y)))

(sin (* 0.5 n y)))

(* n den ; n=normalization


#|

(with-sound (:clipped #f :statistics #t :play #t)

  (let ((gen (make-nxycos 300 1/3 3)))

 (do ((i 0 (+ i 1)))

((= i 2))

   (outa i (* .5 (nxycos gen))

|#


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