Improved BPM detection routine to better spot harmonics for the strongest beat pattern.

3 files changed, 58 insertions, 12 deletions

diff --git a/include/BPMDetect.h b/include/BPMDetect.h
index ff1d3c4..c5989cf 100644
--- a/include/BPMDetect.h
+++ b/include/BPMDetect.h
@@ -67,7 +67,7 @@ namespace soundtouch
 #define MIN_BPM 29

 

 /// Maximum allowed BPM rate. Used to restrict accepted result below a reasonable limit.

-#define MAX_BPM 230

+#define MAX_BPM 200

 

 

 /// Class for calculating BPM rate for audio data.

diff --git a/source/SoundTouch/PeakFinder.cpp b/source/SoundTouch/PeakFinder.cpp
index 9ad601c..cc2113b 100644
--- a/source/SoundTouch/PeakFinder.cpp
+++ b/source/SoundTouch/PeakFinder.cpp
@@ -55,15 +55,46 @@ PeakFinder::PeakFinder()
 }

 

 

+// Finds real 'top' of a peak hump from neighnourhood of the given 'peakpos'.

+int PeakFinder::findTop(const float *data, int peakpos) const

+{

+    int i;

+    int start, end;

+    float refvalue;

+

+    refvalue = data[peakpos];

+

+    // seek within ±10 points

+    start = peakpos - 10;

+    if (start < minPos) start = minPos;

+    end = peakpos + 10;

+    if (end > maxPos) end = maxPos;

+

+    for (i = start; i <= end; i ++)

+    {

+        if (data[i] > refvalue)

+        {

+            peakpos = i;

+            refvalue = data[i];

+        }

+    }

+

+    // failure if max value is at edges of seek range => it's not peak, it's at slope.

+    if ((peakpos == start) || (peakpos == end)) return 0;

+

+    return peakpos;

+}

+

+

 // Finds 'ground level' of a peak hump by starting from 'peakpos' and proceeding

 // to direction defined by 'direction' until next 'hump' after minimum value will 

 // begin

 int PeakFinder::findGround(const float *data, int peakpos, int direction) const

 {

-    float refvalue;

     int lowpos;

     int pos;

     int climb_count;

+    float refvalue;

     float delta;

 

     climb_count = 0;

@@ -210,30 +241,41 @@ double PeakFinder::detectPeak(const float *data, int aminPos, int amaxPos)
     // Now check if the highest peak were in fact harmonic of the true base beat peak 

     // - sometimes the highest peak can be Nth harmonic of the true base peak yet 

     // just a slightly higher than the true base

-    for (i = 2; i < 10; i ++)

+

+    int hp = (int)(highPeak + 0.5);

+

+    for (i = 3; i < 10; i ++)

     {

-        double peaktmp, tmp;

+        double peaktmp, harmonic;

         int i1,i2;

 

-        peakpos = (int)(highPeak / (double)i + 0.5f);

+        harmonic = (double)i * 0.5;

+        peakpos = (int)(highPeak / harmonic + 0.5f);

         if (peakpos < minPos) break;

+        peakpos = findTop(data, peakpos);   // seek true local maximum index

+        if (peakpos == 0) continue;         // no local max here

 

-        // calculate mass-center of possible base peak

+        // calculate mass-center of possible harmonic peak

         peaktmp = getPeakCenter(data, peakpos);

 

+        // accept harmonic peak if 

+        // (a) it is found

+        // (b) is within ±4% of the expected harmonic interval

+        // (c) has at least half x-corr value of the max. peak

+

+        double diff = harmonic * peaktmp / highPeak;

+        if ((diff < 0.96) || (diff > 1.04)) continue;   // peak too afar from expected

+

         // now compare to highest detected peak

         i1 = (int)(highPeak + 0.5);

         i2 = (int)(peaktmp + 0.5);

-        tmp = 2 * (data[i2] - data[i1]) / (data[i2] + data[i1]);

-        if (fabs(tmp) < 0.1)

+        if (data[i2] >= 0.5*data[i1])

         {

-            // The highest peak is harmonic of almost as high base peak,

-            // thus use the base peak instead

+            // The harmonic is at least half as high primary peak,

+            // thus use the harmonic peak instead

             peak = peaktmp;

         }

     }

 

     return peak;

 }

-

-

diff --git a/source/SoundTouch/PeakFinder.h b/source/SoundTouch/PeakFinder.h
index a72b24f..fce4dc1 100644
--- a/source/SoundTouch/PeakFinder.h
+++ b/source/SoundTouch/PeakFinder.h
@@ -63,6 +63,10 @@ protected:
                             int direction       /// Direction where to proceed from the peak: 1 = right, -1 = left.

                             ) const;

 

+    // Finds real 'top' of a peak hump from neighnourhood of the given 'peakpos'.

+    int findTop(const float *data, int peakpos) const;

+

+

     /// Finds the 'ground' level, i.e. smallest level between two neighbouring peaks, to right- 

     /// or left-hand side of the given peak position.

     int   findGround(const float *data,     /// Data vector.