ref: 8605fb3a520aafb2d43febb6c0a9acde871090e7
parent: 5f1d4388b1ba13ca80540f4734bbc58648468e3c
author: Chris Moeller <kode54@gmail.com>
date: Mon Apr 22 19:15:06 EDT 2013
Replaced FIR resampler's IIR low pass filter with a fixed set of cutoff stages
--- a/dumb/src/helpers/fir_resampler.c
+++ b/dumb/src/helpers/fir_resampler.c
@@ -16,8 +16,16 @@
typedef short fir_impulse[fir_adj_width];
-static fir_impulse fir_impulses[fir_max_res];
+/* exp slope to 31/32 of ln(8) */
+static const double fir_ratios[32] = {+ 1.000, 1.067, 1.139, 1.215, 1.297, 1.384, 1.477, 1.576,
+ 1.682, 1.795, 1.915, 2.044, 2.181, 2.327, 2.484, 2.650,
+ 2.828, 3.018, 3.221, 3.437, 3.668, 3.914, 4.177, 4.458,
+ 4.757, 5.076, 5.417, 5.781, 6.169, 6.583, 7.025, 7.497
+};
+static fir_impulse fir_impulses[32][fir_max_res];
+
#undef PI
#define PI 3.1415926535897932384626433832795029
@@ -59,8 +67,7 @@
int read_pos, read_filled;
unsigned short phase;
unsigned int phase_inc;
- float a1, a2, b02, b1;
- float yn1, yn2;
+ unsigned int ratio_set;
int buffer_in[fir_buffer_size * 2];
int buffer_out[fir_buffer_size];
} fir_resampler;
@@ -76,9 +83,7 @@
r->read_filled = 0;
r->phase = 0;
r->phase_inc = 0;
- r->a1 = 0; r->a2 = 0;
- r->b02 = 0; r->b1 = 0;
- r->yn1 = 0; r->yn2 = 0;
+ r->ratio_set = 0;
memset( r->buffer_in, 0, sizeof(r->buffer_in) );
memset( r->buffer_out, 0, sizeof(r->buffer_out) );
@@ -102,12 +107,7 @@
r_out->read_filled = r_in->read_filled;
r_out->phase = r_in->phase;
r_out->phase_inc = r_in->phase_inc;
- r_out->a1 = r_in->a1;
- r_out->a2 = r_in->a2;
- r_out->b02 = r_in->b02;
- r_out->b1 = r_in->b1;
- r_out->yn1 = r_in->yn1;
- r_out->yn2 = r_in->yn2;
+ r_out->ratio_set = r_in->ratio_set;
memcpy( r_out->buffer_in, r_in->buffer_in, sizeof(r_in->buffer_in) );
memcpy( r_out->buffer_out, r_in->buffer_out, sizeof(r_in->buffer_out) );
@@ -134,8 +134,6 @@
r->read_pos = 0;
r->read_filled = 0;
r->phase = 0;
- r->yn1 = 0;
- r->yn2 = 0;
memset( r->buffer_in, 0, sizeof(r->buffer_in) );
}
@@ -143,21 +141,8 @@
{fir_resampler * r = ( fir_resampler * ) _r;
r->phase_inc = (int)( new_factor * 65536.0 );
- if ( r->phase_inc > 65536 )
- {- double omega = 2 * PI * 0.5 / new_factor;
- double cs = cos(omega);
- double sn = sin(omega);
- double alpha = sn / 2.0;
- double a0_inv = 1.0 / (1.0 + alpha);
-
- double b1_temp = (1.0 - cs) * a0_inv;
-
- r->b02 = b1_temp * 0.5;
- r->b1 = b1_temp;
- r->a1 = -2.0 * cs * a0_inv;
- r->a2 = (1.0 - alpha) * a0_inv;
- }
+ r->ratio_set = 0;
+ while ( r->ratio_set < 31 && new_factor > fir_ratios[ r->ratio_set ] ) r->ratio_set++;
}
void fir_resampler_write_sample(void *_r, short s)
@@ -168,18 +153,6 @@
{int s32 = s;
- if ( r->phase_inc > 65536 )
- {- /* The filter is implemented in Direct-II form. */
- float in, out, dsp_centernode;
- in = s32;
- dsp_centernode = in - r->a1 * r->yn1 - r->a2 * r->yn2;
- out = r->b02 * (dsp_centernode + r->yn2) + r->b1 * r->yn1;
- r->yn2 = r->yn1;
- r->yn1 = dsp_centernode;
- s32 = out;
- }
-
r->buffer_in[ r->write_pos ] = s32;
r->buffer_in[ r->write_pos + fir_buffer_size ] = s32;
@@ -196,23 +169,27 @@
int const res = fir_max_res;
- double const ratio_ = 1.0 / (double)fir_max_res;
+ int i;
+
+ for (i = 0; i < 32; i++)
+ {+ double const ratio_ = fir_ratios[ i ];
- double fraction = fmod( ratio_, 1.0 );
+ double fraction = 1.0 / (double)fir_max_res;
- double const filter = (ratio_ < 1.0) ? 1.0 : 1.0 / ratio_;
- double pos = 0.0;
- //int input_per_cycle = 0;
- short* out = (short*) fir_impulses;
- int n;
- for ( n = res; --n >= 0; )
- {- gen_sinc( rolloff, (int) (fir_adj_width * filter + 1) & ~1, pos, filter,
- (double) (0x7FFF * gain * filter), (int) fir_adj_width, out );
- out += fir_adj_width;
+ double const filter = (ratio_ < 1.0) ? 1.0 : 1.0 / ratio_;
+ double pos = 0.0;
+ short* out = (short*) fir_impulses[ i ];
+ int n;
+ for ( n = res; --n >= 0; )
+ {+ gen_sinc( rolloff, (int) (fir_adj_width * filter + 1) & ~1, pos, filter,
+ (double) (0x7FFF * gain * filter), (int) fir_adj_width, out );
+ out += fir_adj_width;
- pos += fraction;
- }
+ pos += fraction;
+ }
+ }
}
int fir_resampler_run(void *_r, int ** out_, int * out_end)
@@ -229,11 +206,12 @@
int const* const in_end = in + in_size;
int phase = r->phase;
int phase_inc = r->phase_inc;
+ int ratio_set = r->ratio_set;
do
{// accumulate in extended precision
- short const* imp = fir_impulses[(phase & 0xFFC0) >> 6];
+ short const* imp = fir_impulses[ratio_set][(phase & 0xFFC0) >> 6];
int pt = imp [0];
int s = pt * in [0];
int n;