bpmdetect.h

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/******************************************************************************
 *
 * 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.
 * - Inputted 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 @ iki.fi
 * File created  : 11-Jan-2003
 *
 * Last changed  : $Date: 2004/03/14 15:51:41 $
 * File revision : $Revision: 1.1.1.1 $
 *
 * $Id: BPMDetect.h,v 1.1.1.1 2004/03/14 15:51:41 mbrubeck Exp $
 *
 * License :
 *
 *  SoundTouch sound 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"

/// Minimum allowed BPM rate. Used to restrict accepted result above a reasonable limit.
#define MIN_BPM 45

/// Maximum allowed BPM rate. Used to restrict accepted result below a reasonable limit.
#define MAX_BPM 230


/// Internal class prototype 
class FIFOSampleBuffer;

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

    /// RMS volume sliding average approximation level accumulator
    float 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.
    FIFOSampleBuffer *buffer;

    /// Initialize the class for processing.
    void init(int numChannels, int sampleRate);

    /// 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 outputted in 'samples.
    void calcEnvelope(soundtouch::SAMPLETYPE *samples,  ///< Pointer to input/output data buffer
                      int numsamples                    ///< Number of samples in buffer
                      );

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 inputted
    /// 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(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 inputted to the class by consecutive calls of
    /// 'inputSamples' function.
    ///
    /// \return Beats-per-minute rate, or zero if detection failed.
	float getBpm();
};

#endif // _BPMDetect_H_