ref: 96de5819111e6f89e310981e49fa52e8b9cae653
dir: /h/butlp.h/
typedef struct {
SPFLOAT sr, freq;
SPFLOAT lfreq;
SPFLOAT a[7];
SPFLOAT pidsr;
} sp_butlp;
int sp_butlp_create(sp_butlp **p);
int sp_butlp_destroy(sp_butlp **p);
int sp_butlp_init(sp_data *sp, sp_butlp *p);
int sp_butlp_compute(sp_data *sp, sp_butlp *p, SPFLOAT *in, SPFLOAT *out);