From bd7ccc5fa05587606757adbacb6e1bf12f12fd2c Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Sat, 28 Jan 2017 18:18:44 +0100
Subject: Add global DC-Filter and remove all individual DC-Filters

---
 src/common/emphasis.c | 10 +++++++---
 src/common/emphasis.h |  1 +
 src/common/goertzel.c | 29 +++++++++--------------------
 src/common/sender.c   |  8 +++++---
 4 files changed, 22 insertions(+), 26 deletions(-)

(limited to 'src/common')

diff --git a/src/common/emphasis.c b/src/common/emphasis.c
index 93c2b6f..524c37b 100644
--- a/src/common/emphasis.c
+++ b/src/common/emphasis.c
@@ -27,7 +27,7 @@
 
 #define PI		M_PI
 
-#define CUT_OFF_H	300.0	/* cut-off frequency for high-pass filters */
+#define CUT_OFF_H	100.0	/* cut-off frequency for high-pass filter */
 
 static void gen_sine(double *samples, int num, int samplerate, double freq)
 {
@@ -106,8 +106,6 @@ void de_emphasis(emphasis_t *state, double *samples, int num)
 	double x, y, y_last, factor, amp;
 	int i;
 
-	filter_process(&state->d.hp, samples, num);
-
 	y_last = state->d.y_last;
 	factor = state->d.factor;
 	amp = state->d.amp;
@@ -126,3 +124,9 @@ void de_emphasis(emphasis_t *state, double *samples, int num)
 	state->d.y_last = y_last;
 }
 
+/* high pass filter to remove DC and low frequencies */
+void dc_filter(emphasis_t *state, double *samples, int num)
+{
+	filter_process(&state->d.hp, samples, num);
+}
+
diff --git a/src/common/emphasis.h b/src/common/emphasis.h
index 53450d8..f14afd1 100644
--- a/src/common/emphasis.h
+++ b/src/common/emphasis.h
@@ -17,4 +17,5 @@ typedef struct emphasis {
 int init_emphasis(emphasis_t *state, int samplerate, double cut_off);
 void pre_emphasis(emphasis_t *state, double *samples, int num);
 void de_emphasis(emphasis_t *state, double *samples, int num);
+void dc_filter(emphasis_t *state, double *samples, int num);
 
diff --git a/src/common/goertzel.c b/src/common/goertzel.c
index eaa7f99..ccfbd12 100644
--- a/src/common/goertzel.c
+++ b/src/common/goertzel.c
@@ -30,30 +30,26 @@
  * audio level calculation
  */
 
-/* return average value (rectified value), that can be 0..1 */
+/* Return average value (rectified value)
+ * The input must not have any dc offset!
+ * For a perfect rectangualr wave, the result would equal the peak level.
+ * For a sine wave the result would be factor (2 / PI) below peak level.
+ */
 double audio_level(sample_t *samples, int length)
 {
-	double bias;
-	double level;
-	int sk;
+	double level, sk;
 	int n;
 
-	/* calculate bias */
-	bias = 0;
-	for (n = 0; n < length; n++)
-		bias += samples[n];
-	bias = bias / length;
-
 	/* level calculation */
 	level = 0;
 	for (n = 0; n < length; n++) {
-		sk = samples[n] - bias;
+		sk = samples[n];
 		if (sk < 0)
 			level -= (double)sk;
 		if (sk > 0)
 			level += (double)sk;
 	}
-	level = level / (double)length / 32767.0;
+	level = level / (double)length;
 
 	return level;
 }
@@ -79,17 +75,10 @@ void audio_goertzel_init(goertzel_t *goertzel, double freq, int samplerate)
  */
 void audio_goertzel(goertzel_t *goertzel, sample_t *samples, int length, int offset, double *result, int k)
 {
-	double bias;
 	double sk, sk1, sk2;
 	double cos2pik;
 	int i, n;
 
-	/* calculate bias to remove DC */
-	bias = 0;
-	for (n = 0; n < length; n++)
-		bias += samples[n];
-	bias = bias / length;
-
 	/* we do goertzel */
 	for (i = 0; i < k; i++) {
 		sk = 0;
@@ -98,7 +87,7 @@ void audio_goertzel(goertzel_t *goertzel, sample_t *samples, int length, int off
 		cos2pik = goertzel[i].coeff;
 		/* note: after 'length' cycles, offset is restored to its initial value */
 		for (n = 0; n < length; n++) {
-			sk = (cos2pik * sk1) - sk2 + samples[offset++] - bias;
+			sk = (cos2pik * sk1) - sk2 + samples[offset++];
 			sk2 = sk1;
 			sk1 = sk;
 			if (offset == length)
diff --git a/src/common/sender.c b/src/common/sender.c
index f63e021..62eec06 100644
--- a/src/common/sender.c
+++ b/src/common/sender.c
@@ -281,7 +281,7 @@ cant_recover:
 				display_wave(inst, samples[i], count);
 				sender_receive(inst, samples[i], count);
 			}
-			/* do pre emphasis towards radio, not wave_write */
+			/* do pre emphasis towards radio */
 			if (inst->pre_emphasis)
 				pre_emphasis(&inst->estate, samples[i], count);
 			/* set paging signal */
@@ -331,9 +331,11 @@ transmit_later:
 			/* rx gain */
 			if (inst->rx_gain != 1.0)
 				gain_samples(samples[i], count, inst->rx_gain);
-			/* do de emphasis from radio (then write_wave/wave_read), receive audio, process echo test */
-			if (inst->de_emphasis)
+			/* do filter and de-emphasis from radio receive audio, process echo test */
+			if (inst->de_emphasis) {
+				dc_filter(&inst->estate, samples[i], count);
 				de_emphasis(&inst->estate, samples[i], count);
+			}
 			if (inst->loopback != 1) {
 				display_wave(inst, samples[i], count);
 				sender_receive(inst, samples[i], count);
-- 
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