Code: Select all

```
;nyquist plug-in
;version 1
;type analyze
;categories "http://audacityteam.org/namespace#OnsetDetector"
;name "Beat Finder..."
;action "Finding beats..."
;author "Audacity"
;copyright "Released under terms of the GNU General Public License version 2"
;; Released under terms of the GNU General Public License version 2:
;; http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;control thresval "Threshold Percentage" int "" 65 5 100
(setf s1 (if (arrayp s) (snd-add (aref s 0) (aref s 1)) s))
(defun signal () (force-srate 1000 (lp (snd-follow (lp s1 50) 0.001 0.01 0.1 512) 10)))
(setq max (peak (signal) NY:ALL))
(setq thres (* (/ thresval 100.0) max))
(setq s2 (signal))
(do ((c 0.0) (l NIL) (p T) (v (snd-fetch s2))) ((not v) l)
(if (and p (> v thres)) (setq l (cons (list c "B") l)))
(setq p (< v thres))
(setq c (+ c 0.001))
(setq v (snd-fetch s2)))
```

I'm kind of new to coding and I'm trying to walk through this lisp code. This is beat.ny, which I assume does beat detection, ie, marking the audio spikes over a certain threshold.

I'm trying to figure out how the threshold detection takes place. Namely: if it's more than merely when a certain sample goes over a threshold -- is there some kind of "root mean square" or weighted average going on?

I think the particular line of interest is this, which I'm not sure how to interpret. It seems to be doing a running average?

Code: Select all

`(defun signal () (force-srate 1000 (lp (snd-follow (lp s1 50) 0.001 0.01 0.1 512) 10)))`