From 71e556e7ffd9e470bde25158b42303eeb2355ff7 Mon Sep 17 00:00:00 2001 From: Andreas Eversberg Date: Sat, 28 Jan 2017 08:02:11 +0100 Subject: [PATCH] Work on emphasis filter: Neutral @ 1000 Hz; Use filter before de-emphasis --- src/cnetz/cnetz.c | 2 +- src/common/debug.c | 4 +- src/common/emphasis.c | 79 +++++++++++++++++++++++++--------------- src/common/emphasis.h | 7 ++-- src/test/test_emphasis.c | 64 ++++++++++++++++---------------- 5 files changed, 88 insertions(+), 68 deletions(-) diff --git a/src/cnetz/cnetz.c b/src/cnetz/cnetz.c index c811ba7..57cd289 100644 --- a/src/cnetz/cnetz.c +++ b/src/cnetz/cnetz.c @@ -143,7 +143,7 @@ /* uncomment this to do echo debugging (-L) on Speech Channel */ //#define DEBUG_SPK -#define CUT_OFF_EMPHASIS_CNETZ 796 /* 200 uS time constant */ +#define CUT_OFF_EMPHASIS_CNETZ 796.0 /* 200 uS time constant */ /* Call reference for calls from mobile station to network This offset of 0x400000000 is required for MNCC interface. */ diff --git a/src/common/debug.c b/src/common/debug.c index fe4de48..ab79b0f 100644 --- a/src/common/debug.c +++ b/src/common/debug.c @@ -126,11 +126,11 @@ const char *debug_db(double level_db) static char text[128]; int l; - strcpy(text, ": . : . : . : . : . : . : . : . : "); + strcpy(text, ": . : . : . : . : . : . : . : . | . : . : . : . : . : . : . : . :"); if (level_db <= 0.0) return text; l = (int)round(level2db(level_db)); - if (l > 3) + if (l > 48) return text; if (l < -48) return text; diff --git a/src/common/emphasis.c b/src/common/emphasis.c index 57273d4..93c2b6f 100644 --- a/src/common/emphasis.c +++ b/src/common/emphasis.c @@ -21,37 +21,60 @@ #include #include #include +#include "filter.h" #include "emphasis.h" #include "debug.h" #define PI M_PI -#define CUT_OFF_H 200.0 /* cut-off frequency for high-pass filters */ +#define CUT_OFF_H 300.0 /* cut-off frequency for high-pass filters */ + +static void gen_sine(double *samples, int num, int samplerate, double freq) +{ + int i; + + for (i = 0; i < num; i++) + samples[i] = cos(2.0 * M_PI * freq / (double)samplerate * (double)i); +} + +static double get_level(double *samples, int num) +{ + int i; + double envelope = 0; + for (i = num/2; i < num; i++) { + if (samples[i] > envelope) + envelope = samples[i]; + } + + return envelope; +} int init_emphasis(emphasis_t *state, int samplerate, double cut_off) { - double factor, rc, dt; + double factor; + double test_samples[samplerate / 10]; memset(state, 0, sizeof(*state)); - if (samplerate < 24000) { - PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be at least 24000 Hz!\n"); - return -1; - } /* exp (-2 * PI * CUT_OFF * delta_t) */ - factor = exp(-2.0 * PI * cut_off / samplerate); /* 1/samplerate == delta_t */ + factor = exp(-2.0 * PI * cut_off / (double)samplerate); /* 1/samplerate == delta_t */ + PDEBUG(DDSP, DEBUG_DEBUG, "Emphasis factor = %.3f\n", factor); state->p.factor = factor; - state->p.amp = samplerate / 6400.0; - state->d.d_factor = factor; - state->d.amp = 1.0 / (samplerate / 5750.0); + state->p.amp = 1.0; + state->d.factor = factor; + state->d.amp = 1.0; + + filter_highpass_init(&state->d.hp, CUT_OFF_H, samplerate, 1); + + /* calibrate amplification to be neutral at 1000 Hz */ + gen_sine(test_samples, sizeof(test_samples) / sizeof(test_samples[0]), samplerate, 1000.0); + pre_emphasis(state, test_samples, sizeof(test_samples) / sizeof(test_samples[0])); + state->p.amp = 1.0 / get_level(test_samples, sizeof(test_samples) / sizeof(test_samples[0])); + gen_sine(test_samples, sizeof(test_samples) / sizeof(test_samples[0]), samplerate, 1000.0); + de_emphasis(state, test_samples, sizeof(test_samples) / sizeof(test_samples[0])); + state->d.amp = 1.0 / get_level(test_samples, sizeof(test_samples) / sizeof(test_samples[0])); - /* high-pass filter prevents low frequency noise and dc level - * from being amplified by de-emphasis */ - rc = 1.0 / (CUT_OFF_H * 2.0 *3.14); - dt = 1.0 / samplerate; - state->d.h_factor = rc / (rc + dt); - PDEBUG(DDSP, DEBUG_DEBUG, "High-Pass factor = %.3f\n", state->d.h_factor); return 0; } @@ -65,13 +88,14 @@ void pre_emphasis(emphasis_t *state, double *samples, int num) amp = state->p.amp; for (i = 0; i < num; i++) { - x = *samples / 32768.0; + x = *samples; + /* pre-emphasis */ y = x - factor * x_last; x_last = x; - *samples++ = (int)(amp * y * 32768.0); + *samples++ = amp * y; } state->p.x_last = x_last; @@ -79,31 +103,26 @@ void pre_emphasis(emphasis_t *state, double *samples, int num) void de_emphasis(emphasis_t *state, double *samples, int num) { - double x, y, z, y_last, z_last, d_factor, h_factor, amp; + double x, y, y_last, factor, amp; int i; + filter_process(&state->d.hp, samples, num); + y_last = state->d.y_last; - z_last = state->d.z_last; - d_factor = state->d.d_factor; - h_factor = state->d.h_factor; + factor = state->d.factor; amp = state->d.amp; for (i = 0; i < num; i++) { - x = *samples / 32768.0; + x = *samples; /* de-emphasis */ - y = x + d_factor * y_last; - - /* high pass */ - z = h_factor * (z_last + y - y_last); + y = x + factor * y_last; y_last = y; - z_last = z; - *samples++ = (int)(amp * z * 32768.0); + *samples++ = amp * y; } state->d.y_last = y_last; - state->d.z_last = z_last; } diff --git a/src/common/emphasis.h b/src/common/emphasis.h index 39d5246..53450d8 100644 --- a/src/common/emphasis.h +++ b/src/common/emphasis.h @@ -5,15 +5,14 @@ typedef struct emphasis { double amp; } p; struct { + filter_t hp; double y_last; - double z_last; - double d_factor; - double h_factor; + double factor; double amp; } d; } emphasis_t; -#define CUT_OFF_EMPHASIS_DEFAULT 300.0 +#define CUT_OFF_EMPHASIS_DEFAULT 300.0 int init_emphasis(emphasis_t *state, int samplerate, double cut_off); void pre_emphasis(emphasis_t *state, double *samples, int num); diff --git a/src/test/test_emphasis.c b/src/test/test_emphasis.c index 79799d2..c5fa1af 100644 --- a/src/test/test_emphasis.c +++ b/src/test/test_emphasis.c @@ -3,6 +3,7 @@ #include #include #include "../common/sample.h" +#include "../common/filter.h" #include "../common/emphasis.h" #include "../common/debug.h" @@ -10,29 +11,17 @@ #define db2level(db) pow(10, (double)db / 20.0) #define SAMPLERATE 48000 -#define DEVIATION 8000.0 -static double test_freq[] = { 25, 50, 100, 200, 250, 300, 400, 500, 1000, 2000, 4000, 0 }; - -static void check_level(sample_t *samples, double freq, const char *desc) +static double get_level(double *samples) { int i; - int last = 0, envelope = 0; - int up = 0; - - for (i = 0; i < SAMPLERATE; i++) { - if (last < samples[i]) { - up = 1; - } else if (last > samples[i]) { - if (up) { - if (last > envelope) - envelope = last; - } - up = 0; - } - last = samples[i]; + double envelope = 0; + for (i = SAMPLERATE/2; i < SAMPLERATE; i++) { + if (samples[i] > envelope) + envelope = samples[i]; } - printf("%s: f = %.0f envelop = %.4f\n", desc, freq, level2db((double)envelope / DEVIATION)); + + return envelope; } static void gen_samples(double *samples, double freq) @@ -41,34 +30,47 @@ static void gen_samples(double *samples, double freq) double value; for (i = 0; i < SAMPLERATE; i++) { - value = sin(2.0 * M_PI * freq / (double)SAMPLERATE * (double)i); - samples[i] = value * DEVIATION; + value = cos(2.0 * M_PI * freq / (double)SAMPLERATE * (double)i); + samples[i] = value; } } int main(void) { emphasis_t estate; + double cut_off = CUT_OFF_EMPHASIS_DEFAULT; double samples[SAMPLERATE]; - int i; + double level; + double i; debuglevel = DEBUG_DEBUG; - printf("1000 Hz shall be close to 0 dB, that is no significant change in volume.\n\n"); + init_emphasis(&estate, SAMPLERATE, cut_off); - init_emphasis(&estate, SAMPLERATE, CUT_OFF_EMPHASIS_DEFAULT); + printf("testing pre-emphasis filter with cut-off frequency %.1f\n", cut_off); - for (i = 0; test_freq[i]; i++) { - gen_samples(samples, test_freq[i]); + for (i = 31.25; i < 4001; i = i * sqrt(sqrt(2.0))) { + gen_samples(samples, (double)i); pre_emphasis(&estate, samples, SAMPLERATE); - check_level(samples, test_freq[i], "pre-emphasis"); + level = get_level(samples); + printf("%s%.0f Hz: %.1f dB", debug_db(level), i, level2db(level)); + if ((int)round(i) == 1000) + printf(" level=%.6f\n", level); + else + printf("\n"); } - /* generate sweep 0..4khz */ - for (i = 0; test_freq[i]; i++) { - gen_samples(samples, test_freq[i]); + printf("testing de-emphasis filter with cut-off frequency %.1f\n", cut_off); + + for (i = 31.25; i < 4001; i = i * sqrt(sqrt(2.0))) { + gen_samples(samples, (double)i); de_emphasis(&estate, samples, SAMPLERATE); - check_level(samples, test_freq[i], "de-emphasis"); + level = get_level(samples); + printf("%s%.0f Hz: %.1f dB", debug_db(level), i, level2db(level)); + if ((int)round(i) == 1000) + printf(" level=%.6f\n", level); + else + printf("\n"); } return 0;