c# - Help with implementing this beat-detection algorithm? -


i tried implement beat detection code found here, namely derivation , combfilter algorithm #1:: http://archive.gamedev.net/reference/programming/features/beatdetection/page2.asp

im not sure if implemented not getting results. wondering if have implemented or towards people want in general. here implementation:

//cycle through tempo's (60 200) incrementing each time 10 (int = (int)mintempo; <= maxtempo; += 10) {     //clear variables used     curtempo = i;     fftpulse.clear();     offset = 0;     energy = 0;     short[] prevbuffer = null;      //calculate ti     ti = (60 / curtempo) * 44100;     ti = math.round(ti, 0);      //generate pulse train     (int j = 0; j < pulsetrain.length; j++)     {         if ((j % ti) == 0)             pulsetrain[j] = short.maxvalue;         else             pulsetrain[j] = 0;     }      //compute fft of pulsetrain array     while (offset < pulsetrain.length)     {         //generate block samples (1024 blocksize)         short[] fftpulsebuffer = new short[po.blocksize / 2];          //store samples pulsetrain in 1024 block buffer passing fft algorithm         index = 0;         (int j = offset; j < (offset + (po.blocksize / 2)) && j < pulsetrain.length; j++)         {             fftpulsebuffer[index] = pulsetrain[j];             index++;         }          //initialize prevbuffer, contains samples previous block, used in conjunction current block fft         if (prevbuffer == null)             prevbuffer = new short[po.blocksize / 2];          //calculate fft using current , previous blocks         fftpulse.add(calculatefft(fftpulsebuffer,prevbuffer));          //set prevbuffer , increment next block start position         prevbuffer = fftpulsebuffer;         offset += (po.blocksize / 2);     }  //calculate energy     (int j = 0; j < intendomainarr.count; j++)     {         double[] signalarr = intendomainarr[j];         double[] pulsearr = fftpulse[j];         (int x = 0; x < signalarr.length; x++)         {             energy += math.abs(signalarr[x] * pulsearr[x]);         }     }      //get current best tempo match     if (energy > maxenergy)     {         chosentempo = curtempo;         maxenergy = energy;     } }

the results getting high, around 190 , 200bpm, should not case, .wav files have tempos between 60-120bpm.

note using .wav file (44.1khz, 16-bit, mono), of formulas bit modified (i.e. calculating energy) work 1 channel. confirm if there have been discrepancies in implementation? not worrying fft part because using library that.

thank much!

make plot of energy vs frequency.

i think you'll find harmonics have identical energy base signal, , if actual frequency falls halfway between frequency bins, second harmonic's peak sampled , beats 2 samples either side of true frequency.

you'll need penalize higher frequencies little bit overcome effect.

please note, while c# not unreasonable choice implementation of such algorithm in real time or bulk batch processing, it's horrible algorithm development , tweaking. i'd recommend using matlab (or free clone, octave) algorithm right, , once it's working on test cases, convert code c# (or c++).


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