text: /* FluidSynth - A Software Synthesizer
   *
   * Copyright (C) 2003  Peter Hanappe and others.
   *
   * 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., 51 Franklin Street, Fifth Floor, Boston, MA
   * 02110-1301, USA
   */
  
  #ifndef _FLUID_IIR_FILTER_H
  #define _FLUID_IIR_FILTER_H
  
  #include "fluidsynth_priv.h"
  
  typedef struct _fluid_iir_filter_t fluid_iir_filter_t;
  
  DECLARE_FLUID_RVOICE_FUNCTION(fluid_iir_filter_init);
  DECLARE_FLUID_RVOICE_FUNCTION(fluid_iir_filter_set_fres);
  DECLARE_FLUID_RVOICE_FUNCTION(fluid_iir_filter_set_q);
  
  void fluid_iir_filter_apply(fluid_iir_filter_t *iir_filter,
                              fluid_real_t *dsp_buf, int dsp_buf_count);
  
  void fluid_iir_filter_reset(fluid_iir_filter_t *iir_filter);
  
  void fluid_iir_filter_calc(fluid_iir_filter_t *iir_filter,
                             fluid_real_t output_rate,
                             fluid_real_t fres_mod);
  
  /* We can't do information hiding here, as fluid_voice_t includes the struct
     without a pointer. */
  struct _fluid_iir_filter_t
  {
      enum fluid_iir_filter_type type; /* specifies the type of this filter */
      enum fluid_iir_filter_flags flags; /* additional flags to customize this filter */
  
      /* filter coefficients */
      /* The coefficients are normalized to a0. */
      /* b0 and b2 are identical => b02 */
      fluid_real_t b02;              /* b0 / a0 */
      fluid_real_t b1;              /* b1 / a0 */
      fluid_real_t a1;              /* a0 / a0 */
      fluid_real_t a2;              /* a1 / a0 */
  
      fluid_real_t b02_incr;
      fluid_real_t b1_incr;
      fluid_real_t a1_incr;
      fluid_real_t a2_incr;
      int filter_coeff_incr_count;
      int compensate_incr;		/* Flag: If set, must compensate history */
      fluid_real_t hist1, hist2;      /* Sample history for the IIR filter */
      int filter_startup;             /* Flag: If set, the filter will be set directly.
  					   Else it changes smoothly. */
  
      fluid_real_t fres;              /* the resonance frequency, in cents (not absolute cents) */
      fluid_real_t last_fres;         /* Current resonance frequency of the IIR filter */
      /* Serves as a flag: A deviation between fres and last_fres */
      /* indicates, that the filter has to be recalculated. */
      fluid_real_t q_lin;             /* the q-factor on a linear scale */
      fluid_real_t filter_gain;       /* Gain correction factor, depends on q */
  };
  
  #endif
  
  