aicodix___dsp/filter.hh

/*
Some finite impulse response filter functions

Copyright 2018 Ahmet Inan <inan@aicodix.de>
*/

#pragma once

#include "const.hh"
#include "utils.hh"
#include "unit_circle.hh"

namespace DSP {

template <typename TYPE>
class LowPass
{
	TYPE f;
public:
	LowPass(TYPE cutoff) : f(TYPE(2) * cutoff) {}
	TYPE operator () (int n, int N)
	{
		TYPE x = TYPE(n) - TYPE(0.5) * TYPE(N - 1);
		return f * sinc(f * x);
	}
};

template <typename TYPE>
class LowPass2
{
	int num, den;
	TYPE fac;
public:
	LowPass2(int num, int den) : num(num), den(den), fac(TYPE(2*num)/TYPE(den)) {}
	TYPE operator () (int n, int N)
	{
		int twox = 2 * n - (N - 1);
		return !twox ? fac : fac *
			UnitCircle<TYPE>::sin((twox * num) % (2 * den), 2 * den) /
			(Const<TYPE>::HalfPi() * fac * TYPE(twox));
	}
};

template <typename TYPE>
class HighPass
{
	TYPE f;
public:
	HighPass(TYPE cutoff) : f(TYPE(2) * cutoff) {}
	TYPE operator () (int n, int N)
	{
		TYPE x = TYPE(n) - TYPE(0.5) * TYPE(N - 1);
		// if (N%1) return delta(x) - f * sinc(f * x);
		return sinc(x) - f * sinc(f * x);

	}
};

template <typename TYPE>
class BandPass
{
	TYPE f0, f1;
public:
	BandPass(TYPE cutoff0, TYPE cutoff1) :
		f0(TYPE(2) * cutoff0), f1(TYPE(2) * cutoff1) {}
	TYPE operator () (int n, int N)
	{
		TYPE x = TYPE(n) - TYPE(0.5) * TYPE(N - 1);
		return f1 * sinc(f1 * x) - f0 * sinc(f0 * x);
	}
};

}