libbeatnik: Calculate score from thresholded input

beatnik-calculate-score-from-thresholded-input.patch

diff --git a/include/re/beatnik/tracker/tracker.hpp b/include/re/beatnik/tracker/tracker.hpp
index 8c29389..ec83a0b 100644
--- a/include/re/beatnik/tracker/tracker.hpp
+++ b/include/re/beatnik/tracker/tracker.hpp
@@ -34,6 +34,13 @@ public:
     bool
     update_score(T odf_value) noexcept
     {
+
+        threshold_sum += odf_value;
+        threshold_buffer.push_back(odf_value);
+        auto in = threshold_buffer[threshold_size / 2];
+        auto out = std::fdim(in, threshold_sum / (threshold_size + 1));
+        threshold_sum -= threshold_buffer.front();
+
         if (!is_valid_period(period_guess)) {
             return false;
         }
@@ -44,7 +51,7 @@ public:
             cumulative_score.rend()
         );

-        auto new_score = (1 - alpha) * odf_value + alpha * last_score.value;
+        auto new_score = (1 - alpha) * out + alpha * last_score.value;
         cumulative_score.push_back(new_score);
         // a distance from the last beat
         backlink.push_back(static_cast<int_t>(last_score.index));
@@ -108,14 +115,17 @@ private:
                && period < max_period;
     }

-    static constexpr float alpha = 0.9f;
+    static constexpr float alpha = 0.8f;
     static constexpr int_t N = min_period * beats_count;
+    static constexpr int_t threshold_size = 14;

     int_t period_guess;
     int_t counter;
     ring_array <T, N> cumulative_score;
     ring_array <int_t, N> backlink;
     skewed_window <T, min_period> window;
+    T threshold_sum;
+    ring_array<T, threshold_size> threshold_buffer;
 };

 }
 diff --git a/include/re/beatnik/tracker/skewed_window.hpp b/include/re/beatnik/tracker/skewed_window.hpp
index e1e1ef2..dc312dd 100644
--- a/include/re/beatnik/tracker/skewed_window.hpp
+++ b/include/re/beatnik/tracker/skewed_window.hpp
@@ -73,7 +73,7 @@ private:
         return std::exp(-.5f * std::pow(TIGHTNESS * std::log(2 - x), 2.f));
     };

-    static constexpr T TIGHTNESS = 5;
+    static constexpr T TIGHTNESS = 3;
     std::array<std::array<T, row_size>, period_range> cache;
 };