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;
};

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);