From f921e1474dcb13f1b11daba6ce3c746b3eae5528 Mon Sep 17 00:00:00 2001
From: markster <markster@5390a7c7-147a-4af0-8ec9-7488f05a26cb>
Date: Sun, 14 Apr 2002 02:29:01 +0000
Subject: Version 0.2.0 from FTP

git-svn-id: http://svn.digium.com/svn/zaptel/trunk@78 5390a7c7-147a-4af0-8ec9-7488f05a26cb
---
 ecdis.h | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100755 ecdis.h

diff --git a/ecdis.h b/ecdis.h
new file mode 100755
index 0000000..4d3801b
--- /dev/null
+++ b/ecdis.h
@@ -0,0 +1,118 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * ec_disable_detector.h - A detector which should eventually meet the
+ *                         G.164/G.165 requirements for detecting the
+ *                         2100Hz echo cancellor disable tone.
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2001 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+#include "biquad.h"
+
+typedef struct
+{
+    biquad2_state_t notch;
+    int notch_level;
+    int channel_level;
+    int tone_present;
+    int tone_cycle_duration;
+    int good_cycles;
+    int hit;
+} echo_can_disable_detector_state_t;
+
+
+#define FALSE 0
+#define TRUE (!FALSE)
+
+static inline void echo_can_disable_detector_init (echo_can_disable_detector_state_t *det)
+{
+    /* Elliptic notch */
+    /* This is actually centred at 2095Hz, but gets the balance we want, due
+       to the asymmetric walls of the notch */
+    biquad2_init (&det->notch,
+    	     	  (int32_t) (-0.7600000*32768.0),
+    	    	  (int32_t) (-0.1183852*32768.0),
+    	    	  (int32_t) (-0.5104039*32768.0),
+    	    	  (int32_t) ( 0.1567596*32768.0),
+    	    	  (int32_t) ( 1.0000000*32768.0));
+
+    det->channel_level = 0;
+    det->notch_level = 0;    
+    det->tone_present = FALSE;
+    det->tone_cycle_duration = 0;
+    det->good_cycles = 0;
+    det->hit = 0;
+}
+/*- End of function --------------------------------------------------------*/
+
+static inline int echo_can_disable_detector_update (echo_can_disable_detector_state_t *det,
+                                      int16_t amp)
+{
+    int16_t notched;
+    
+    	notched = biquad2 (&det->notch, amp);
+    	/* Estimate the overall energy in the channel, and the energy in
+	   the notch (i.e. overall channel energy - tone energy => noise).
+	   Use abs instead of multiply for speed (is it really faster?).
+	   Damp the overall energy a little more for a stable result.
+	   Damp the notch energy a little less, so we don't damp out the
+	   blip every time the phase reverses */
+        det->channel_level += ((abs(amp) - det->channel_level) >> 5);
+	det->notch_level += ((abs(notched) - det->notch_level) >> 4);
+  	if (det->channel_level > 280)
+	{
+	    /* There is adequate energy in the channel. Is it mostly at 2100Hz? */
+	    if (det->notch_level*6 < det->channel_level)
+	    {
+                /* The notch says yes, so we have the tone. */
+		if (!det->tone_present)
+		{
+                    /* Do we get a kick every 450+-25ms? */
+		    if (det->tone_cycle_duration >= 425*8
+			&&
+			det->tone_cycle_duration <= 475*8)
+	            {
+			det->good_cycles++;
+			if (det->good_cycles > 2)
+			    det->hit = TRUE;
+		    }
+		    det->tone_cycle_duration = 0;
+		}
+		det->tone_present = TRUE;
+	    }
+	    else
+	    {
+		det->tone_present = FALSE;
+	    }
+   	    det->tone_cycle_duration++;
+	}
+	else
+	{
+	    det->tone_present = FALSE;
+	    det->tone_cycle_duration = 0;
+	    det->good_cycles = 0;
+	}
+    return  det->hit;
+}
+/*- End of function --------------------------------------------------------*/
+/*- End of file ------------------------------------------------------------*/
-- 
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