filter.h

// Pithesiser - a software synthesiser for Raspberry Pi
// Copyright (C) 2015 Nicholas Tuckett
// 
// This program 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.
// 
// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

/*
 * filter.h
 *
 *  Created on: 3 Feb 2013
 *      Author: ntuckett
 */

#ifndef FILTER_H_
#define FILTER_H_

#include "system_constants.h"

#define FILTER_PASS	0
#define FILTER_LPF	1
#define FILTER_HPF	2

#define FILTER_FIXED_PRECISION	14
#define FILTER_FIXED_ONE		(1 << FILTER_FIXED_PRECISION)

#define FILTER_MIN_Q			(FIXED_ONE / 100)
#define FILTER_MAX_Q			(FIXED_ONE)

#define FILTER_STATE_OFF		FILTER_PASS
#define FILTER_STATE_LAST		FILTER_HPF
#define FILTER_MIN_FREQUENCY	(FILTER_FIXED_ONE * 20)
#define FILTER_MAX_FREQUENCY	(18000 * FILTER_FIXED_ONE)

typedef struct filter_definition_t
{
	int		type;
	fixed_t	frequency;
	fixed_t	gain;
	fixed_t q;
} filter_definition_t;

typedef struct filter_state_t
{
	fixed_t input_coeff[3];
	fixed_t output_coeff[2];
	fixed_t history[2];
	fixed_t output[2];
} filter_state_t;

typedef struct filter_t
{
	filter_definition_t	definition;
	int					updated;
	filter_state_t		state;
	int					last_type;
	filter_state_t		last_state;
} filter_t;

extern void filter_init(filter_t *filter);
extern void filter_update(filter_t *filter);
extern void filter_silence(filter_t *filter);
extern void filter_apply(filter_t *filter, sample_t *sample_data, int sample_count);
extern int filter_definitions_same(filter_definition_t *definition1, filter_definition_t *definition2);

#endif /* FILTER_H_ */