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Source/Helmholtz.h

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+#ifndef Helmholtz_H
+#define Helmholtz_H
+
+
+/***********************************************************************
+
+Class Helmholtz implements a period-length detector using Philip McLeod's
+Specially Normalized AutoCorrelation function (SNAC).
+
+Function iosamples() takes a pointer to a buffer with n signal input samples
+and a pointer to a buffer where n output samples are stored,
+representing the SNAC function.
+
+Via function setframesize(), analysis frame size can be set to
+128, 256, 512, 1024 or 2048 samples. Default is 1024.
+
+With setoverlap(), analysis frames can be set to overlap each other
+with factor 1, 2, 4 or 8. Default is 1.
+
+Function setbias() sets a bias which favours small lags over large lags in
+the period detection, thereby avoiding low-octave jumps. Default is 0.2
+
+Function setminRMS() is used as a sensitivity setting. Default is RMS 0.003.
+
+With function getperiod(), the last detected period length is returned
+as number of samples with a possible fraction (floating point format).
+
+Function getfidelity() returns a value between 0. and 1. indicating
+to which extent the input signal is periodic. A fidelity of ~0.95 can
+be considered to indicate a periodic signal.
+
+Class Helmholtz needs mayer_realfft() and mayer_realifft() or similar
+fft functions. Note that Ron Mayer's functions for real fft have a
+peculiar organisation of imaginary coefficients (reversed order, sign flipped).
+
+Class Helmholtz uses t_float for float or double. Depending on the context
+where the class is used, you may need to define t_float. If used with
+PD or MaxMsp, it is already defined.
+
+***********************************************************************
+
+Licensed under three-clause BSD license.
+
+Katja Vetter, Feb 2012.
+
+***********************************************************************/
+
+/* This section includes the Pure Data API header. If you build Helmholtz
+against another DSP framework, you need to define t_float, and you need to
+include Ron Mayer's fft or similar functionality. */
+
+#include "mayer_fft.h"
+#define REALFFT mayer_realfft
+#define REALIFFT mayer_realifft
+
+/***********************************************************************/
+
+#define DEFFRAMESIZE 1024       // default analysis framesize
+#define DEFOVERLAP 1            // default overlap
+#define DEFBIAS 0.2             // default bias
+#define DEFMINRMS 0.003         // default minimum RMS 
+#define SEEK 0.85               // seek-length as ratio of framesize
+
+#define t_float float
+
+class Helmholtz
+{
+public:
+    Helmholtz(int periodarg = DEFFRAMESIZE, int overlaparg = DEFOVERLAP, t_float biasarg = DEFBIAS);
+
+    ~Helmholtz();
+    void iosamples(const t_float* in, t_float* out, int size);
+    void setframesize(int frame);
+    void setoverlap(int lap);
+    void setbias(t_float bias);
+    void setminRMS(t_float rms);
+    t_float getperiod() const;
+    t_float getfidelity() const;
+
+private:
+    // procedures
+    void analyzeframe();
+    void autocorrelation();
+    void normalize();
+    void pickpeak();
+    void periodandfidelity();
+
+    // functions
+    t_float interpolate3max(t_float* buf, int peakindex);
+    t_float interpolate3phase(t_float* buf, int peakindex);
+
+    // buffers
+    t_float inputbuf[2048];
+    t_float inputbuf2[2048];
+    t_float processbuf[4096];
+
+    // state variables
+    int timeindex;
+    int framesize;
+    int overlap;
+    int periodindex;
+
+    t_float periodlength;
+    t_float fidelity;
+    t_float biasfactor;
+    t_float minrms;
+};
+
+#endif // #ifndef Helmholtz_H