Slight reworking of API params for phase-response and pass-/stop-band spec

3 files changed, 33 insertions, 25 deletions

diff --git a/src/rate.h b/src/rate.h
index fc2395c..81cabff 100644
--- a/src/rate.h
+++ b/src/rate.h
@@ -369,7 +369,7 @@ typedef struct {
 #define have_post_stage (postM * postL != 1)
 
 #define TO_3dB(a)       ((1.6e-6*a-7.5e-4)*a+.646)
-#define LOW_Q_BW0_PC    (67 + 5 / 8.)
+#define LOW_Q_BW0       (1385 / 2048.) /* 0.67625 rounded to be a FP exact. */
 
 typedef enum {
   rolloff_none, rolloff_small /* <= 0.01 dB */, rolloff_medium /* <= 0.35 dB */
@@ -385,9 +385,9 @@ static char const * rate_init(
   double factor,             /* Input rate divided by output rate.            */
   double bits,               /* Required bit-accuracy (pass + stop)  16|20|28 */
   double phase,              /* Linear/minimum etc. filter phase.       50    */
-  double bw_pc,              /* Pass-band % (0dB pt.) to preserve.   91.3|98.4*/
-  double anti_aliasing_pc,   /* % bandwidth without aliasing            100   */
-  rolloff_t rolloff,    /* Pass-band roll-off                    small   */
+  double passband_end,       /* 0dB pt. bandwidth to preserve; nyquist=1 0.913*/
+  double stopband_begin,     /* Aliasing/imaging control; > passband_end  1   */
+  rolloff_t rolloff,         /* Pass-band roll-off                    small   */
   bool maintain_3dB_pt,      /*                                        true   */
   double multiplier,         /* Linear gain to apply during conversion.   1   */
 
@@ -400,20 +400,20 @@ static char const * rate_init(
   int log2_large_dft_size)
 {
   double att = (bits + 1) * linear_to_dB(2.), attArb = att;    /* pass + stop */
-  double tbw0 = 1 - bw_pc / 100, Fs_a = 2 - anti_aliasing_pc / 100;
+  double tbw0 = 1 - passband_end, Fs_a = stopband_begin;
   double arbM = factor, tbw_tighten = 1;
   int n = 0, i, preL = 1, preM = 1, shift = 0, arbL = 1, postL = 1, postM = 1;
   bool upsample = false, rational = false, iOpt = !noSmallIntOpt;
-  int mode = rolloff > rolloff_small? factor > 1 || bw_pc > LOW_Q_BW0_PC:
+  int mode = rolloff > rolloff_small? factor > 1 || passband_end > LOW_Q_BW0:
     (int)ceil(2 + (bits - 17) / 4);
   stage_t * s;
 
   assert(factor > 0);
   assert(!bits || (15 <= bits && bits <= 33));
   assert(0 <= phase && phase <= 100);
-  assert(53 <= bw_pc && bw_pc <= 100);
-  assert(85 <= anti_aliasing_pc && anti_aliasing_pc <= 130);
-  assert(bw_pc < 200 - anti_aliasing_pc);
+  assert(.53 <= passband_end);
+  assert(stopband_begin <= 1.2);
+  assert(passband_end + .005 < stopband_begin);
 
   p->factor = factor;
   if (bits) while (!n++) {                               /* Determine stages: */
@@ -690,9 +690,9 @@ static char const * rate_create(
       channel, shared,
       io_ratio,
       q_spec->precision,
-      q_spec->phase,
-      q_spec->bw_pc,
-      q_spec->anti_aliasing_pc,
+      q_spec->phase_response,
+      q_spec->passband_end,
+      q_spec->stopband_begin,
       "\1\2\0"[q_spec->flags & 3],
       !!(q_spec->flags & SOXR_MAINTAIN_3DB_PT),
       scale,
diff --git a/src/soxr.c b/src/soxr.c
index 457144b..8a9eca6 100644
--- a/src/soxr.c
+++ b/src/soxr.c
@@ -69,7 +69,7 @@ struct soxr {
 
 /* TODO: these should not be here. */
 #define TO_3dB(a)       ((1.6e-6*a-7.5e-4)*a+.646)
-#define LOW_Q_BW0_PC    (67 + 5 / 8.)
+#define LOW_Q_BW0       (1385 / 2048.) /* 0.67625 rounded to be a FP exact. */
 
 soxr_quality_spec_t soxr_quality_spec(unsigned long recipe, unsigned long flags)
 {
@@ -85,24 +85,24 @@ soxr_quality_spec_t soxr_quality_spec(unsigned long recipe, unsigned long flags)
     quality = 6;
   else if (quality > 10)
     quality = 0;
-  p->phase = "\62\31\144"[(recipe & 0x30)>>8];
-  p->anti_aliasing_pc = 100;
+  p->phase_response = "\62\31\144"[(recipe & 0x30)>>8];
+  p->stopband_begin = 1;
   p->precision = !quality? 0: quality < 3? 16 : quality < 8? 4 + quality * 4 : 55 - quality * 4;
   rej = p->precision * linear_to_dB(2.);
   p->flags = flags;
   if (quality < 8) {
-    p->bw_pc = quality == 1? LOW_Q_BW0_PC : 100 - 5 / TO_3dB(rej);
+    p->passband_end = quality == 1? LOW_Q_BW0 : 1 - .05 / TO_3dB(rej);
     if (quality <= 2)
       p->flags &= ~SOXR_ROLLOFF_NONE, p->flags |= SOXR_ROLLOFF_MEDIUM;
   }
   else {
-    static float const bw[] = {93.1f, 83.2f, 66.3f};
-    p->bw_pc = bw[quality - 8];
+    static float const bw[] = {.931f, .832f, .663f};
+    p->passband_end = bw[quality - 8];
     if (quality - 8 == 2)
       p->flags &= ~SOXR_ROLLOFF_NONE, p->flags |= SOXR_ROLLOFF_MEDIUM;
   }
   if (recipe & SOXR_STEEP_FILTER)
-    p->bw_pc = 100 - 1 / TO_3dB(rej);
+    p->passband_end = 1 - .01 / TO_3dB(rej);
   return spec;
 }
 
@@ -217,6 +217,14 @@ soxr_t soxr_create(
 
   if (p) {
     p->q_spec = q_spec? *q_spec : soxr_quality_spec(SOXR_HQ, 0);
+
+    if (q_spec) { /* Backwards compatibility with original API: */
+      if (p->q_spec.passband_end > 2)
+        p->q_spec.passband_end /= 100;
+      if (p->q_spec.stopband_begin > 2)
+        p->q_spec.stopband_begin = 2 - p->q_spec.stopband_begin / 100;
+    }
+
     p->io_ratio = io_ratio;
     p->num_channels = num_channels;
     if (io_spec)
diff --git a/src/soxr.h b/src/soxr.h
index bcc7bff..aa7960d 100644
--- a/src/soxr.h
+++ b/src/soxr.h
@@ -221,12 +221,12 @@ struct soxr_io_spec {                                            /* Typically */
 
 
 struct soxr_quality_spec {                                       /* Typically */
-  double precision;          /* Conversion precision (in bits).         20    */
-  double phase;              /* Linear/minimum etc. phase. [0,100]      50    */
-  double bw_pc;              /* Band-width % (0dB pt.) to preserve.    91.3   */
-  double anti_aliasing_pc;   /* % bandwidth without aliasing.           100   */
-  void * e;                  /* Reserved for internal use.               0    */
-  unsigned long flags;       /* Per the following #defines.              0    */
+  double precision;         /* Conversion precision (in bits).           20   */
+  double phase_response;    /* 0=minimum, ... 50=linear, ... 100=maximum 50   */
+  double passband_end;      /* 0dB pt. bandwidth to preserve; nyquist=1  0.913*/
+  double stopband_begin;    /* Aliasing/imaging control; > passband_end   1   */
+  void * e;                 /* Reserved for internal use.                 0   */
+  unsigned long flags;      /* Per the following #defines.                0   */
 };
 
 #define SOXR_ROLLOFF_SMALL     0u    /* <= 0.01 dB */