I'm forwarding this to the Audacity developer & nyquist lists in case somebody there has comments.
- Vaughan Albert Santoni wrote: > Hi Enr(r)y, > > Without actually knowing the Nyquist language, I think what this code > is doing is: > - Downsampling to 1000 Hz (the Nyquist frequency is then 500 Hz, and > there's tons of aliasing introduced probably. I think aliasing is the > right term to use...?) > - applying a low-pass filter (so that you just get the bassy beat, > probably kills the aliasing caused by the downsampling) > - If signal > threshold, we've found a peak > > I wouldn't be surprised if there was some other stuff going on in this > code, but it's not immediately obvious that there is. The algorithm I > extracted above would be pretty easy to write in C++ if someone is > bored and wants to play around with it. It could be the start of a new > BPM detection algorithm even* (that's optimistic though). :) > > Thanks, > Albert > > * If someone wants to hack a new algorithm in, look at bpmdetector.cpp > and just hack a new BPM detection function in there. You'll see two > existing functions in there for doing BPM detection, so you'd just add > another. > > > > > On 7-Jan-09, at 2:23 AM, [email protected] wrote: > > >> Hi all, this is enrry. >> >> I have seen a nice feature of Audacity software: it's "beat finder", >> you can try from analysis tab, it is not perfect and maybe a little >> trivial, but looks to work rather well and I think it could be >> someway integrated to make Mixxx beat pattern manage to be >> synchronized with the first beat of a track. >> >> In Audacity user can set threshold parameter and select a part of >> audio file to be analyzed; here in Mixxx i think that it would be >> enough to analyze the first 10-20 s of the track. >> >> Here is the source code of beat finder written in Nyquist language: >> do someone know it and would be interested to convert in C++ and >> integrate into bpm and pattern algorhitms? >> >> ;nyquist plug-in >> ;version 1 >> ;type analyze >> ;categories "http://audacityteam.org/namespace#OnsetDetector"; >> ;n! ame "Beat Finder..." >> ;action "Finding beats..." >> ;info "Released under terms of the GNU General Public License >> version 2" >> >> ;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))) >> >> ; arch-tag: 2204686b-2dcc-4891-964a-2749ac30661b >> > ------------------------------------------------------------------------------ This SF.net email is sponsored by: SourcForge Community SourceForge wants to tell your story. http://p.sf.net/sfu/sf-spreadtheword _______________________________________________ Mixxx-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/mixxx-devel
