ls_filter.h

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#ifndef LS_FILTER_H
#define LS_FILTER_H
 
#include <util/biquad.h>
 
#define FILT_MIDI_2_FREQ(m) (m * 80.0f + 10.0f)
#define FILT_MIDI_2_RESO(m) (m * 0.00787f)
 
#define LSF_BW 0.9
#define LSF_FB 0.9f
 
typedef struct {
    biquad filt;
    biquad bp_filt;
    bq_t scale;
    bq_t resonance;
} ls_filt;
 
typedef enum {
    LS_FILT_TYPE_LP = 0,
    LS_FILT_TYPE_BP = 1,
    LS_FILT_TYPE_HP = 2
} ls_filt_type;
 
static inline void ls_filt_init(ls_filt *f)
{
        biquad_init(&(f->filt));
        biquad_init(&(f->bp_filt));
}
 
static inline void ls_filt_setup(ls_filt *f, ls_filt_type t, bq_t cutoff,
                                 bq_t resonance, bq_t fs)
{
        bp_set_params(&(f->bp_filt), cutoff, 0.7, fs);
 
        switch(t) {
        case LS_FILT_TYPE_LP:
                lp_set_params(&(f->filt), cutoff, 1.0 - resonance * LSF_BW, fs);
                break;
        case LS_FILT_TYPE_BP:
                bp_set_params(&(f->filt), cutoff, 1.0 - resonance * LSF_BW, fs);
                break;
        case LS_FILT_TYPE_HP:
                hp_set_params(&(f->filt), cutoff, 1.0 - resonance * LSF_BW, fs);
                break;
        default:
                /* oops, its not a known type - should really happen, but
                   lets make the output silent just in case */
                lp_set_params(&(f->filt), 1.0, 1.0, fs);
                break;
        }
 
        f->scale = 1.0f - resonance * 0.7f;
        f->resonance = resonance;
}
 
static inline bq_t ls_filt_run(ls_filt *f, bq_t in)
{
        return biquad_run(&(f->filt), in) * f->scale +
          biquad_run_fb(&(f->bp_filt), in, f->resonance * LSF_FB) *
          f->resonance;
}
 
#endif