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);