Correct the bsinc filter order

Despite the claim that it was an 11th order filter, the transition width was
generated by specifying 12th order. A 12th order filter would need 14 sample
points rather than the 12 it had.

1 files changed, 7 insertions, 6 deletions

diff --git a/utils/bsincgen.c b/utils/bsincgen.c
index 76047968..657c78ca 100644
--- a/utils/bsincgen.c
+++ b/utils/bsincgen.c
@@ -47,6 +47,7 @@
 

 #define BSINC_REJECTION (60.0)

 #define BSINC_POINTS_MIN (12)

+#define BSINC_ORDER (11)

 

 static double MinDouble(double a, double b)

 { return (a <= b) ? a : b; }

@@ -147,7 +148,7 @@ static void BsiGenerateTables()
        band, but it may vary due to the linear interpolation between scales

        of the filter.

     */

-    width = CalcKaiserWidth(BSINC_REJECTION, BSINC_POINTS_MIN);

+    width = CalcKaiserWidth(BSINC_REJECTION, BSINC_ORDER);

     beta = CalcKaiserBeta(BSINC_REJECTION);

     scaleBase = width / 2.0;

     scaleRange = 1.0 - scaleBase;

@@ -242,19 +243,19 @@ static void BsiGenerateTables()
         i += 4 * BSINC_PHASE_COUNT * mt[si];

 

     fprintf(stdout, "/* Generated by bsincgen, do not edit! */\n\n"

-"/* Table of windowed sinc coefficients and deltas.  This 11th order filter\n"

-" * has a rejection of -60 dB, yielding a transition width of ~0.302\n"

+"/* Table of windowed sinc coefficients and deltas.  This %dth order filter\n"

+" * has a rejection of -%gdB, yielding a transition width of ~%.3f\n"

 " * (normalized frequency).  Order increases when downsampling to a limit of\n"

 " * one octave, after which the quality of the filter (transition width)\n"

 " * suffers to reduce the CPU cost.  The bandlimiting will cut all sound after\n"

-" * downsampling by ~2.73 octaves.\n"

+" * downsampling by ~%.2f octaves.\n"

 " */\n"

 "static const struct {\n"

 "    alignas(16) const float Tab[%d];\n"

 "    const float scaleBase, scaleRange;\n"

 "    const int m[BSINC_SCALE_COUNT];\n"

 "    const int filterOffset[BSINC_SCALE_COUNT];\n"

-"} bsinc = {\n", i);

+"} bsinc = {\n", BSINC_ORDER, BSINC_REJECTION, width, log2(1.0/scaleBase), i);

 

     fprintf(stdout, "    /* Tab */ {\n");

     for(si = 0; si < BSINC_SCALE_COUNT; si++)

@@ -321,7 +322,7 @@ static void Sinc4GenerateTables(void)
 {

     static double filter[FRACTIONONE][4];

 

-    const double width = CalcKaiserWidth(BSINC_REJECTION, 4);

+    const double width = CalcKaiserWidth(BSINC_REJECTION, 3);

     const double beta = CalcKaiserBeta(BSINC_REJECTION);

     const double scaleBase = width / 2.0;

     const double scaleRange = 1.0 - scaleBase;