diff options
Diffstat (limited to 'utils')
| -rw-r--r-- | utils/bsincgen.c | 57 |
1 files changed, 29 insertions, 28 deletions
diff --git a/utils/bsincgen.c b/utils/bsincgen.c index be9940c3..15813e36 100644 --- a/utils/bsincgen.c +++ b/utils/bsincgen.c @@ -49,10 +49,10 @@ #define BSINC_SCALE_COUNT (16)
#define BSINC_PHASE_COUNT (16)
-#define BSINC_REJECTION (60.0)
-#define BSINC_POINTS_MIN (12)
-#define BSINC_ORDER (BSINC_POINTS_MIN - 1)
-#define BSINC_POINTS_MAX (BSINC_POINTS_MIN * 2)
+/* 24 points includes the doubling for downsampling. So the maximum allowed
+ * order is 11, which is 12 sample points that multiplied by 2 is 24.
+ */
+#define BSINC_POINTS_MAX (24)
static double MinDouble(double a, double b)
{ return (a <= b) ? a : b; }
@@ -104,8 +104,8 @@ static double Kaiser(const double b, const double k) return BesselI_0(b * sqrt(1.0 - k*k)) / BesselI_0(b);
}
-/* NOTE: Calculates the transition width of the Kaiser window. Rejection is
- * in dB.
+/* Calculates the (normalized frequency) transition width of the Kaiser window.
+ * Rejection is in dB.
*/
static double CalcKaiserWidth(const double rejection, const int order)
{
@@ -113,7 +113,7 @@ static double CalcKaiserWidth(const double rejection, const int order) if(rejection > 21.0)
return (rejection - 7.95) / (order * 2.285 * w_t);
-
+ /* This enforces a minimum rejection of just above 21.18dB */
return 5.79 / (order * w_t);
}
@@ -128,7 +128,7 @@ static double CalcKaiserBeta(const double rejection) }
/* Generates the coefficient, delta, and index tables required by the bsinc resampler */
-static void BsiGenerateTables(const char *tabname)
+static void BsiGenerateTables(const char *tabname, const double rejection, const int order)
{
static double filter[BSINC_SCALE_COUNT][BSINC_PHASE_COUNT + 1][BSINC_POINTS_MAX];
static double scDeltas[BSINC_SCALE_COUNT][BSINC_PHASE_COUNT ][BSINC_POINTS_MAX];
@@ -136,6 +136,7 @@ static void BsiGenerateTables(const char *tabname) static double spDeltas[BSINC_SCALE_COUNT][BSINC_PHASE_COUNT ][BSINC_POINTS_MAX];
static int mt[BSINC_SCALE_COUNT];
static double at[BSINC_SCALE_COUNT];
+ const int num_points_min = order + 1;
double width, beta, scaleBase, scaleRange;
int si, pi, i;
@@ -148,8 +149,8 @@ static void BsiGenerateTables(const char *tabname) band, but it may vary due to the linear interpolation between scales
of the filter.
*/
- width = CalcKaiserWidth(BSINC_REJECTION, BSINC_ORDER);
- beta = CalcKaiserBeta(BSINC_REJECTION);
+ width = CalcKaiserWidth(rejection, order);
+ beta = CalcKaiserBeta(rejection);
scaleBase = width / 2.0;
scaleRange = 1.0 - scaleBase;
@@ -157,9 +158,8 @@ static void BsiGenerateTables(const char *tabname) for(si = 0; si < BSINC_SCALE_COUNT; si++)
{
const double scale = scaleBase + (scaleRange * si / (BSINC_SCALE_COUNT - 1));
- const double a = MinDouble(floor(BSINC_POINTS_MIN / (2.0 * scale)),
- BSINC_POINTS_MIN);
- int m = 2 * (int)a;
+ const double a = MinDouble(floor(num_points_min / (2.0 * scale)), num_points_min);
+ const int m = 2 * (int)a;
mt[si] = m;
at[si] = a;
@@ -171,7 +171,7 @@ static void BsiGenerateTables(const char *tabname) for(si = 0; si < BSINC_SCALE_COUNT; si++)
{
const int m = mt[si];
- const int o = BSINC_POINTS_MIN - (m / 2);
+ const int o = num_points_min - (m / 2);
const int l = (m / 2) - 1;
const double a = at[si];
const double scale = scaleBase + (scaleRange * si / (BSINC_SCALE_COUNT - 1));
@@ -198,7 +198,7 @@ static void BsiGenerateTables(const char *tabname) for(si = 0; si < (BSINC_SCALE_COUNT - 1); si++)
{
const int m = mt[si];
- const int o = BSINC_POINTS_MIN - (m / 2);
+ const int o = num_points_min - (m / 2);
for(pi = 0; pi < BSINC_PHASE_COUNT; pi++)
{
@@ -211,7 +211,7 @@ static void BsiGenerateTables(const char *tabname) for(si = 0; si < BSINC_SCALE_COUNT; si++)
{
const int m = mt[si];
- const int o = BSINC_POINTS_MIN - (m / 2);
+ const int o = num_points_min - (m / 2);
for(pi = 0; pi < BSINC_PHASE_COUNT; pi++)
{
@@ -226,7 +226,7 @@ static void BsiGenerateTables(const char *tabname) for(si = 0; si < (BSINC_SCALE_COUNT - 1); si++)
{
const int m = mt[si];
- const int o = BSINC_POINTS_MIN - (m / 2);
+ const int o = num_points_min - (m / 2);
for(pi = 0; pi < BSINC_PHASE_COUNT; pi++)
{
@@ -257,17 +257,17 @@ static void BsiGenerateTables(const char *tabname) " const float scaleBase, scaleRange;\n"
" const int m[BSINC_SCALE_COUNT];\n"
" const int filterOffset[BSINC_SCALE_COUNT];\n"
-"} %s = {\n", BSINC_ORDER, (((BSINC_ORDER%100)/10) == 1) ? "th" :
- ((BSINC_ORDER%10) == 1) ? "st" :
- ((BSINC_ORDER%10) == 2) ? "nd" :
- ((BSINC_ORDER%10) == 3) ? "rd" : "th",
- BSINC_REJECTION, width, log2(1.0/scaleBase), i, tabname);
+"} %s = {\n", order, (((order%100)/10) == 1) ? "th" :
+ ((order%10) == 1) ? "st" :
+ ((order%10) == 2) ? "nd" :
+ ((order%10) == 3) ? "rd" : "th",
+ rejection, width, log2(1.0/scaleBase), i, tabname);
fprintf(stdout, " /* Tab */ {\n");
for(si = 0; si < BSINC_SCALE_COUNT; si++)
{
const int m = mt[si];
- const int o = BSINC_POINTS_MIN - (m / 2);
+ const int o = num_points_min - (m / 2);
for(pi = 0; pi < BSINC_PHASE_COUNT; pi++)
{
@@ -324,12 +324,12 @@ static void BsiGenerateTables(const char *tabname) #define FRACTIONBITS (12)
#define FRACTIONONE (1<<FRACTIONBITS)
-static void Sinc4GenerateTables(void)
+static void Sinc4GenerateTables(const double rejection)
{
static double filter[FRACTIONONE][4];
- const double width = CalcKaiserWidth(BSINC_REJECTION, 3);
- const double beta = CalcKaiserBeta(BSINC_REJECTION);
+ const double width = CalcKaiserWidth(rejection, 3);
+ const double beta = CalcKaiserBeta(rejection);
const double scaleBase = width / 2.0;
const double scaleRange = 1.0 - scaleBase;
const double scale = scaleBase + scaleRange;
@@ -358,7 +358,8 @@ static void Sinc4GenerateTables(void) int main(void)
{
- BsiGenerateTables("bsinc");
- Sinc4GenerateTables();
+ /* An 11th order filter with a -60dB drop at nyquist. */
+ BsiGenerateTables("bsinc", 60.0, 11);
+ Sinc4GenerateTables(60.0);
return 0;
}
|