Add missing file.

diff --git a/correlation_measurer.cpp b/correlation_measurer.cpp
new file mode 100644 (file)
index 0000000..888ebff
--- /dev/null
+++ b/correlation_measurer.cpp
@@ -0,0 +1,67 @@
+// Adapted from Adriaensen's project Zita-mu1 (as of January 2016).
+// Original copyright follows:
+//
+//  Copyright (C) 2008-2015 Fons Adriaensen <fons@linuxaudio.org>
+//    
+//  This program is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation; either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include "correlation_measurer.h"
+
+#include <assert.h>
+#include <stdint.h>
+#include <math.h>
+
+using namespace std;
+
+CorrelationMeasurer::CorrelationMeasurer(unsigned sample_rate,
+                                         float lowpass_cutoff_hz,
+                                        float falloff_seconds)
+    : w1(2.0 * M_PI * lowpass_cutoff_hz / sample_rate),
+      w2(1.0 / (falloff_seconds * sample_rate))
+{
+}
+
+void CorrelationMeasurer::process_samples(const std::vector<float> &samples)
+{
+       assert(samples.size() % 2 == 0);
+
+       // The compiler isn't always happy about modifying members,
+       // since it doesn't always know they can't alias on <samples>.
+       // Help it out a bit.
+       float l = zl, r = zr, ll = zll, lr = zlr, rr = zrr;
+       const float w1c = w1, w2c = w2;
+
+       for (size_t i = 0; i < samples.size(); i += 2) {
+               // The 1e-15f epsilon is to avoid denormals.
+               // TODO: Just set the SSE flush-to-zero flags instead.
+               l += w1c * (samples[i + 0] - l) + 1e-15f;
+               r += w1c * (samples[i + 1] - r) + 1e-15f;
+               lr += w2c * (l * r - lr);
+               ll += w2c * (l * l - ll);
+               rr += w2c * (r * r - rr);
+       }
+
+       zl = l;
+       zr = r;
+       zll = ll;
+       zlr = lr;
+       zrr = rr;
+}
+
+float CorrelationMeasurer::get_correlation() const
+{
+       // The 1e-12f epsilon is to avoid division by zero.
+       // zll and zrr are both always non-negative, so we do not risk negative values.
+       return zlr / sqrt(zll * zrr + 1e-12f);
+}

diff --git a/correlation_measurer.h b/correlation_measurer.h
new file mode 100644 (file)
index 0000000..6d84340
--- /dev/null
+++ b/correlation_measurer.h
@@ -0,0 +1,55 @@
+#ifndef _CORRELATION_MEASURER_H
+#define _CORRELATION_MEASURER_H 1
+
+// Measurement of left/right stereo correlation. +1 is pure mono
+// (okay but not ideal), 0 is no correlation (usually bad, unless
+// it is due to silence), strongly negative values means inverted
+// phase (bad). Typical values for e.g. music would be somewhere
+// around +0.7, although you can expect it to vary a bit.
+//
+// This is, of course, based on the regular Pearson correlation,
+// where µ_L and µ_R is taken to be 0 (ie., no DC offset). It is
+// filtered through a simple IIR filter so that older values are
+// weighed less than newer, depending on <falloff_seconds>.
+//
+//
+// Adapted from Adriaensen's project Zita-mu1 (as of January 2016).
+// Original copyright follows:
+//
+//  Copyright (C) 2008-2015 Fons Adriaensen <fons@linuxaudio.org>
+//    
+//  This program is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation; either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include <vector>
+
+class CorrelationMeasurer {
+public:
+       CorrelationMeasurer(unsigned sample_rate, float lowpass_cutoff_hz = 1000.0f,
+                           float falloff_seconds = 0.150f);
+       void process_samples(const std::vector<float> &samples);  // Taken to be stereo, interleaved.
+       float get_correlation() const;
+
+private:
+       float w1, w2;
+
+       // Filtered values of left and right channel, respectively.
+       float zl = 0.0f, zr = 0.0f;
+
+       // Filtered values of l², r² and lr (where l and r are the filtered
+       // versions, given by zl and zr). Together, they make up what we need
+       // to calculate the correlation.
+       float zll = 0.0f, zlr = 0.0f, zrr = 0.0f;
+};
+
+#endif  // !defined(_CORRELATION_MEASURER_H)