source: src/temporal/filter.h @ 970bced

/*
  Copyright (C) 2003-2009 Paul Brossier <piem@aubio.org>

  This file is part of aubio.

  aubio 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.

  aubio 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 aubio.  If not, see <http://www.gnu.org/licenses/>.

*/

#ifndef FILTER_H
#define FILTER_H

/** \file 

  Digital filter

  This object stores a digital filter of order \f$n\f$ for \f$c\f$ channels.
  It contains the following data:
    - \f$ n*1 b_i \f$ feedforward coefficients 
    - \f$ n*1 a_i \f$ feedback coefficients 
    - \f$ n*c x_i \f$ input signal
    - \f$ n*c y_i \f$ output signal

  For convenience, the samplerate of the input signal is also stored in the
  object.

  Feedforward and feedback parameters can be modified using
  aubio_filter_get_feedback() and aubio_filter_get_feedforward().

  The function aubio_filter_do_outplace() computes the following output signal
  \f$ y[n] \f$ from the input signal \f$ x[n] \f$:
 
  \f{eqnarray*}{
     y[n] = b_0 x[n] & + & b_1 x[n-1] + b_2 x[n-2] + ... + b_P x[n-P] \\
                     & - & a_1 y[n-1] - a_2 y[n-2] - ... - a_P y[n-P] \\
  \f}

  The function aubio_filter_do() executes the same computation but modifies
  directly the input signal (in-place).

  The function aubio_filter_do_filtfilt() version runs the filter twice, first
  forward then backward, to compensate with the phase shifting of the forward
  operation.

  Some convenience functions are provided: 
    - new_aubio_filter_a_weighting() and aubio_filter_set_a_weighting(),
    - new_aubio_filter_c_weighting() and aubio_filter_set_c_weighting().
 
*/

#ifdef __cplusplus
extern "C" {
#endif

/** Digital filter

*/
typedef struct _aubio_filter_t aubio_filter_t;

/** filter input vector (in-place)

  \param f filter object as returned by new_aubio_filter()
  \param in input vector to filter

*/
void aubio_filter_do (aubio_filter_t * f, fvec_t * in);

/** filter input vector (out-of-place)

  \param f filter object as returned by new_aubio_filter()
  \param in input vector to filter
  \param out output vector to store filtered input

*/
void aubio_filter_do_outplace (aubio_filter_t * f, fvec_t * in, fvec_t * out);

/** filter input vector forward and backward

  \param f ::aubio_filter_t object as returned by new_aubio_filter()
  \param in ::fvec_t input vector to filter
  \param tmp memory space to use for computation

*/
void aubio_filter_do_filtfilt (aubio_filter_t * f, fvec_t * in, fvec_t * tmp);

/** returns a pointer to feedback coefficients \f$ a_i \f$

  \param f filter object to get parameters from

  \return a pointer to the \f$ a_0 ... a_i ... a_P \f$ coefficients

*/
lvec_t *aubio_filter_get_feedback (aubio_filter_t * f);

/** returns a pointer to feedforward coefficients \f$ b_i \f$

  \param f filter object to get coefficients from

  \return a pointer to the \f$ b_0 ... b_i ... b_P \f$ coefficients

*/
lvec_t *aubio_filter_get_feedforward (aubio_filter_t * f);

/** get order of the filter

  \param f filter to get order from

  \return the order of the filter

*/
uint_t aubio_filter_get_order (aubio_filter_t * f);

/** get sampling rate of the filter

  \param f filter to get sampling rate from

  \return the sampling rate of the filter, in Hz

*/
uint_t aubio_filter_get_samplerate (aubio_filter_t * f);

/** create new filter object

  This function creates a new ::aubio_filter_t object, given an order 
  and a specific number of channels.

  \param samplerate signal sampling rate
  \param order order of the filter (number of coefficients)
  \param channels number of channels to allocate

  \return the newly created filter object

*/
aubio_filter_t *new_aubio_filter (uint_t samplerate, uint_t order,
    uint_t channels);

/** delete a filter object
 
  \param f filter object to delete

*/
void del_aubio_filter (aubio_filter_t * f);

#ifdef __cplusplus
}
#endif

#endif /*FILTER_H*/