audacity-nyquist@... schrieb am 04.02.05 20:22:29:
> Hello group,
> I'm fairly new to Audacity. I'm trying to write a simple plugin to
> demodulate 1 kHz AM pulses into a series of square pulses. I also need to
> mark the raise and fall edge of every pulse on the label track or at least
> capture the time mark of each edge. The input signal is simple - just a
> series of 1kHz tones of various widths separated by silence. The sound
> looks like this http://polaris.umuc.edu/~vgokoyev/wwvb__2e8c5c23.gif (the
> buttom channel). I was trying to use the snd-follow function but all I
> could manage is get a half-wave (like the signal was passed through a
> diode). Do you have any suggestions on how to accomplish this? I was not
> able to find many resources/examples for solving this type of problem. I
> did read the nyquist manual and the demo scripts but they most of the time
> show how to modulate a new signal and I need to do a reverse.
> Thank you
Quick Tip: The Beatfinder from the Windows-zip-Distribution (Audacity 1.2.3)
is something similar:
;name "Beat Finder..."
;action "Finding beats..."
;control thresval "Threshold" int "%" 85 50 100
(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)))
unfortunately not much time yet - more later - edgar
important information: snd-abs and snd-sqrt functions are not implemented in
official Audacity 1.2.3 - I think dominic has fixed this (cvs head - audacity 1.3)
but you have to compile yourself if you need these functions!
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