audacity/lib-src/soundtouch/include/BPMDetect.h

////////////////////////////////////////////////////////////////////////////////
///
/// Beats-per-minute (BPM) detection routine.
///
/// The beat detection algorithm works as follows:
/// - Use function 'inputSamples' to input a chunks of samples to the class for
///   analysis. It's a good idea to enter a large sound file or stream in smallish
///   chunks of around few kilosamples in order not to extinguish too much RAM memory.
/// - Input sound data is decimated to approx 500 Hz to reduce calculation burden,
///   which is basically ok as low (bass) frequencies mostly determine the beat rate.
///   Simple averaging is used for anti-alias filtering because the resulting signal
///   quality isn't of that high importance.
/// - Decimated sound data is enveloped, i.e. the amplitude shape is detected by
///   taking absolute value that's smoothed by sliding average. Signal levels that
///   are below a couple of times the general RMS amplitude level are cut away to
///   leave only notable peaks there.
/// - Repeating sound patterns (e.g. beats) are detected by calculating short-term 
///   autocorrelation function of the enveloped signal.
/// - After whole sound data file has been analyzed as above, the bpm level is 
///   detected by function 'getBpm' that finds the highest peak of the autocorrelation 
///   function, calculates it's precise location and converts this reading to bpm's.
///
/// Author        : Copyright (c) Olli Parviainen
/// Author e-mail : oparviai 'at' iki.fi
/// SoundTouch WWW: http://www.surina.net/soundtouch
///
////////////////////////////////////////////////////////////////////////////////
//
// Last changed  : $Date: 2012-08-30 22:53:44 +0300 (Thu, 30 Aug 2012) $
// File revision : $Revision: 4 $
//
// $Id: BPMDetect.h 150 2012-08-30 19:53:44Z oparviai $
//
////////////////////////////////////////////////////////////////////////////////
//
// License :
//
//  SoundTouch audio processing library
//  Copyright (c) Olli Parviainen
//
//  This library is free software; you can redistribute it and/or
//  modify it under the terms of the GNU Lesser General Public
//  License as published by the Free Software Foundation; either
//  version 2.1 of the License, or (at your option) any later version.
//
//  This library 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
//  Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with this library; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
////////////////////////////////////////////////////////////////////////////////

#ifndef _BPMDetect_H_
#define _BPMDetect_H_

#include "STTypes.h"
#include "FIFOSampleBuffer.h"

namespace soundtouch
{

/// Minimum allowed BPM rate. Used to restrict accepted result above a reasonable limit.
#define MIN_BPM 29

/// Maximum allowed BPM rate. Used to restrict accepted result below a reasonable limit.
#define MAX_BPM 200


/// Class for calculating BPM rate for audio data.
class BPMDetect
{
protected:
    /// Auto-correlation accumulator bins.
    float *xcorr;
    
    /// Amplitude envelope sliding average approximation level accumulator
    double envelopeAccu;

    /// RMS volume sliding average approximation level accumulator
    double RMSVolumeAccu;

    /// Sample average counter.
    int decimateCount;

    /// Sample average accumulator for FIFO-like decimation.
    soundtouch::LONG_SAMPLETYPE decimateSum;

    /// Decimate sound by this coefficient to reach approx. 500 Hz.
    int decimateBy;

    /// Auto-correlation window length
    int windowLen;

    /// Number of channels (1 = mono, 2 = stereo)
    int channels;

    /// sample rate
    int sampleRate;

    /// Beginning of auto-correlation window: Autocorrelation isn't being updated for
    /// the first these many correlation bins.
    int windowStart;
 
    /// FIFO-buffer for decimated processing samples.
    soundtouch::FIFOSampleBuffer *buffer;

    /// Updates auto-correlation function for given number of decimated samples that 
    /// are read from the internal 'buffer' pipe (samples aren't removed from the pipe 
    /// though).
    void updateXCorr(int process_samples      /// How many samples are processed.
                     );

    /// Decimates samples to approx. 500 Hz.
    ///
    /// \return Number of output samples.
    int decimate(soundtouch::SAMPLETYPE *dest,      ///< Destination buffer
                 const soundtouch::SAMPLETYPE *src, ///< Source sample buffer
                 int numsamples                     ///< Number of source samples.
                 );

    /// Calculates amplitude envelope for the buffer of samples.
    /// Result is output to 'samples'.
    void calcEnvelope(soundtouch::SAMPLETYPE *samples,  ///< Pointer to input/output data buffer
                      int numsamples                    ///< Number of samples in buffer
                      );

    /// remove constant bias from xcorr data
    void removeBias();

public:
    /// Constructor.
    BPMDetect(int numChannels,  ///< Number of channels in sample data.
              int sampleRate    ///< Sample rate in Hz.
              );

    /// Destructor.
    virtual ~BPMDetect();

    /// Inputs a block of samples for analyzing: Envelopes the samples and then
    /// updates the autocorrelation estimation. When whole song data has been input
    /// in smaller blocks using this function, read the resulting bpm with 'getBpm' 
    /// function. 
    /// 
    /// Notice that data in 'samples' array can be disrupted in processing.
    void inputSamples(const soundtouch::SAMPLETYPE *samples,    ///< Pointer to input/working data buffer
                      int numSamples                            ///< Number of samples in buffer
                      );


    /// Analyzes the results and returns the BPM rate. Use this function to read result
    /// after whole song data has been input to the class by consecutive calls of
    /// 'inputSamples' function.
    ///
    /// \return Beats-per-minute rate, or zero if detection failed.
    float getBpm();
};

}

#endif // _BPMDetect_H_