[2nd order IIR] 2nd order IIR(Infinite-duration Impulse Response) #matlab #2nd_IIR #C #Multimedia_Systems

2nd order IIR.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// def const val
#define SAMPLING_BIT 16

// def struct confficients for IIR
typedef struct __IIRConfficients {
	double b0, b1, b2;
	double a1, a2;
} __IIRConfficients;

// def struct sound file(.snd) information
typedef struct __RawFileInfo {
	char* file_name;
	int sample_bit;
} __RawFileInfo;

// def struct i/o file ptr
typedef struct __ioFile {
	FILE* fi;
	FILE* fo;
} __ioFile;


// file open function
__ioFile file_open(__RawFileInfo input, __RawFileInfo output) {
	// init file ptr
	__ioFile _ioFile = { NULL, NULL };

	fopen_s(&_ioFile.fi, input.file_name, "rb");	// 녹음한 오디오 화일을 연다
	fopen_s(&_ioFile.fo, output.file_name, "wb");	// 출력을 저장할 화일을 연다
	if (_ioFile.fi == NULL && _ioFile.fo == NULL) {
		fputs("file err, press any key.", stderr);
		getchar();
		exit;
	}

	return _ioFile;
}


// 2nd order IIR filter function
void second_order_IIR_filter(__RawFileInfo fi, __RawFileInfo fo, __IIRConfficients conf)
{
	// file open
	__ioFile _ioFile = file_open(fi, fo);

	int i;
	int N;
	__int16 input, output;

	//init x, y
	float x[3] = { 0, 0, 0 };
	float y[3] = { 0, 0, 0 };

	//get file byte size
	fseek(_ioFile.fi, 0, SEEK_END);
	int file_size = ftell(_ioFile.fi);
	fseek(_ioFile.fi, 0, SEEK_SET);

	// 루프횟수 N = 화일에 들어 있는 샘플 수 
	N = file_size / (fi.sample_bit / 8);

	// filtering
	for (i = 0; i < N; i++) {
		x[2] = x[1];		// x[n] 어레이를 한 샘플씩 delay 시킨다.
		x[1] = x[0];
		y[2] = y[1];		// y[n] 어레이를 한 샘플씩 delay 시킨다.
		y[1] = y[0];

		// 입력 PCM(16비트 정수)을 읽어서 x[0] 위치에 넣는다
		fread(&input, sizeof(__int16), 1, _ioFile.fi);
		x[0] = (double)(input);

		// y[n]을 계산한다
		y[0] = conf.b0 * x[0] + conf.b1 * x[1] + conf.b2 * x[2]
								- conf.a1 * y[1] - conf.a2 * y[2];

		// 출력을 16bit PCM 형태로 화일에 저장한다.
		output = (__int16)(y[0]);
		fwrite(&output, sizeof(__int16), 1, _ioFile.fo);
	}

	//close input, output file
	fclose(_ioFile.fi);
	fclose(_ioFile.fo);
}


// main function
int main()
{
	// init vals
	__RawFileInfo file_input = { "sound.snd", SAMPLING_BIT };
	__RawFileInfo high_pass_filter = { "high_pass_filter.snd", SAMPLING_BIT };
	__RawFileInfo low_pass_filter = { "low_pass_filter.snd", SAMPLING_BIT };

	// vals get using matlab(butter function)
	__IIRConfficients HPF = { 0.0604985076309406, 0.120997015261881, 0.0604985076309406, -1.19391336772058, 0.435907398244341 };
	__IIRConfficients LPF = { 0.569035593728849, -1.13807118745770, 0.569035593728849, -0.942809041582064, 0.333333333333333 };

	// filtering
	second_order_IIR_filter(file_input, high_pass_filter, HPF);
	second_order_IIR_filter(file_input, low_pass_filter, LPF);

	// end
	printf("End of program, press any key...\n");
	getchar();
	return 0;
}

IIR_Coefficients.m

clc;        % Clear the command window.
clear;      % Clear workspace variable
close all;  % Clear figure windows

% low pass filter
fs = 16000;
fn = fs/2;
fc = 1500;

n = 2;
ftype = 'low';

[lB, lA] = butter(n, fc/fn, ftype);

% high pass filter
fs = 16000;
fn = fs/2;
fc = 2000;

n = 2;
ftype = 'high';

[hB, hA] = butter(n, fc/fn, ftype);