struct filter_t
{
	double k;
	double r;
	double v_l;
	double v_r;
	double last_in_l;
	double last_in_r;
	double last_out_l;
	double last_out_r;
};

struct bw_filter_t
{
	double a1;
	double a2;
	double a3;
	double b1;
	double b2;

	double in1_l, in2_l, out1_l, out2_l;
	double in1_r, in2_r, out1_r, out2_r;
};

void filter_init_rc(struct filter_t *filter, double R, double C);
void filter_init_freq(struct filter_t *filter, double freq);
void filter_run_lp(struct filter_t *filter, double left, double right);
void filter_run_hp(struct filter_t *filter, double left, double right);

void bw_filter_init_lp(struct bw_filter_t *f, double freq, double resonance);
void bw_filter_run(struct bw_filter_t *f, double in_l, double in_r, double *out_l, double *out_r);