teensy-audio/filter_biquad.h

/* Audio Library for Teensy 3.X
 * Copyright (c) 2014, Paul Stoffregen, paul@pjrc.com
 *
 * Development of this audio library was funded by PJRC.COM, LLC by sales of
 * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
 * open source software by purchasing Teensy or other PJRC products.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice, development funding notice, and this permission
 * notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#ifndef filter_biquad_h_
#define filter_biquad_h_

#include "Arduino.h"
#include "AudioStream.h"

class AudioFilterBiquad : public AudioStream
{
public:
	AudioFilterBiquad(void) : AudioStream(1, inputQueueArray) {
		// by default, the filter will not pass anything
		for (int i=0; i<32; i++) definition[i] = 0;
	}
	virtual void update(void);

	// Set the biquad coefficients directly
	void setCoefficients(uint32_t stage, const int *coefficients);
	void setCoefficients(uint32_t stage, const double *coefficients) {
		int coef[5];
		coef[0] = coefficients[0] * 1073741824.0;
		coef[1] = coefficients[1] * 1073741824.0;
		coef[2] = coefficients[2] * 1073741824.0;
		coef[3] = coefficients[3] * 1073741824.0;
		coef[4] = coefficients[4] * 1073741824.0;
		setCoefficients(stage, coef);
	}

	// Compute common filter functions
	// http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
	void setLowpass(uint32_t stage, float frequency, float q = 0.7071) {
		int coef[5];
		double w0 = frequency * (2 * 3.141592654 / AUDIO_SAMPLE_RATE_EXACT);
		double sinW0 = sin(w0);
		double alpha = sinW0 / ((double)q * 2.0);
		double cosW0 = cos(w0);
		double scale = 1073741824.0 / (1.0 + alpha);
		/* b0 */ coef[0] = ((1.0 - cosW0) / 2.0) * scale;
		/* b1 */ coef[1] = (1.0 - cosW0) * scale;
		/* b2 */ coef[2] = coef[0];
		/* a1 */ coef[3] = (-2.0 * cosW0) * scale;
		/* a2 */ coef[4] = (1.0 - alpha) * scale;
		setCoefficients(stage, coef);
	}
	void setHighpass(uint32_t stage, float frequency, float q = 0.7071) {
		int coef[5];
		double w0 = frequency * (2 * 3.141592654 / AUDIO_SAMPLE_RATE_EXACT);
		double sinW0 = sin(w0);
		double alpha = sinW0 / ((double)q * 2.0);
		double cosW0 = cos(w0);
		double scale = 1073741824.0 / (1.0 + alpha);
		/* b0 */ coef[0] = ((1.0 + cosW0) / 2.0) * scale;
		/* b1 */ coef[1] = -(1.0 + cosW0) * scale;
		/* b2 */ coef[2] = coef[0];
		/* a1 */ coef[3] = (-2.0 * cosW0) * scale;
		/* a2 */ coef[4] = (1.0 - alpha) * scale;
		setCoefficients(stage, coef);
	}
	void setBandpass(uint32_t stage, float frequency, float q = 1.0) {
		int coef[5];
		double w0 = frequency * (2 * 3.141592654 / AUDIO_SAMPLE_RATE_EXACT);
		double sinW0 = sin(w0);
		double alpha = sinW0 / ((double)q * 2.0);
		double cosW0 = cos(w0);
		double scale = 1073741824.0 / (1.0 + alpha);
		/* b0 */ coef[0] = alpha * scale;
		/* b1 */ coef[1] = 0;
		/* b2 */ coef[2] = (-alpha) * scale;
		/* a1 */ coef[3] = (-2.0 * cosW0) * scale;
		/* a2 */ coef[4] = (1.0 - alpha) * scale;
		setCoefficients(stage, coef);
	}
	void setNotch(uint32_t stage, float frequency, float q = 1.0) {
		int coef[5];
		double w0 = frequency * (2 * 3.141592654 / AUDIO_SAMPLE_RATE_EXACT);
		double sinW0 = sin(w0);
		double alpha = sinW0 / ((double)q * 2.0);
		double cosW0 = cos(w0);
		double scale = 1073741824.0 / (1.0 + alpha);
		/* b0 */ coef[0] = scale;
		/* b1 */ coef[1] = (-2.0 * cosW0) * scale;
		/* b2 */ coef[2] = coef[0];
		/* a1 */ coef[3] = (-2.0 * cosW0) * scale;
		/* a2 */ coef[4] = (1.0 - alpha) * scale;
		setCoefficients(stage, coef);
	}

private:
	int32_t definition[32];  // up to 4 cascaded biquads
	audio_block_t *inputQueueArray[1];
};

#endif