diff --git a/src/coding/gsm0503_amr_dtx.c b/src/coding/gsm0503_amr_dtx.c
index b149330..7de3b28 100644
--- a/src/coding/gsm0503_amr_dtx.c
+++ b/src/coding/gsm0503_amr_dtx.c
@@ -1,5 +1,5 @@
 /*
- * (C) 2020 by sysmocom - s.f.m.c. GmbH, Author: Philipp Maier
+ * (C) 2020-2022 by sysmocom - s.f.m.c. GmbH, Author: Philipp Maier
  * All Rights Reserved
  *
  * SPDX-License-Identifier: GPL-2.0+
@@ -32,6 +32,8 @@
 #include <osmocom/coding/gsm0503_parity.h>
 #include <osmocom/gsm/gsm0503.h>
 
+#define S2U(b)	((b) < 0)
+
 /* See also: 3GPP TS 05.03, chapter 3.10.1.3, 3.10.5.2 Identification marker */
 static const ubit_t id_marker_1[] = { 1, 0, 1, 1, 0, 0, 0, 0, 1 };
 
@@ -60,7 +62,7 @@
 	{ 0, NULL }
 };
 
-static bool detect_afs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset, uint8_t count,
+static bool detect_afs_id_marker(int *n_errors, int *n_bits_total, const sbit_t *sbits, uint8_t offset, uint8_t count,
 				 const ubit_t * id_marker, uint8_t id_marker_len)
 {
 	unsigned int i, k;
@@ -69,20 +71,20 @@
 	int bits = 0;
 
 	/* Override coded in-band data */
-	ubits += offset;
+	sbits += offset;
 
 	/* Check for identification marker bits */
 	for (i = 0; i < count; i++) {
 		for (k = 0; k < 4; k++) {
-			if (id_marker[id_bit_nr % id_marker_len] != *ubits)
+			if (*sbits == 0 || id_marker[id_bit_nr % id_marker_len] != S2U(*sbits))
 				errors++;
 			id_bit_nr++;
-			ubits++;
+			sbits++;
 			bits++;
 		}
 
 		/* Jump to the next block of 4 bits */
-		ubits += 4;
+		sbits += 4;
 	}
 
 	*n_errors = errors;
@@ -92,30 +94,30 @@
 	return *n_errors < *n_bits_total / 8;
 }
 
-static bool detect_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, const ubit_t * id_marker)
+static bool detect_ahs_id_marker(int *n_errors, int *n_bits_total, const sbit_t *sbits, const ubit_t *id_marker)
 {
 	unsigned int i, k;
 	int errors = 0;
 	int bits = 0;
 
 	/* Override coded in-band data */
-	ubits += 16;
+	sbits += 16;
 
 	/* Check first identification marker bits (23*9 bits) */
 	for (i = 0; i < 23; i++) {
 		for (k = 0; k < 9; k++) {
-			if (id_marker[k] != *ubits)
+			if (*sbits == 0 || id_marker[k] != S2U(*sbits))
 				errors++;
-			ubits++;
+			sbits++;
 			bits++;
 		}
 	}
 
 	/* Check remaining identification marker bits (5 bits) */
 	for (k = 0; k < 5; k++) {
-		if (id_marker[k] != *ubits)
+		if (*sbits == 0 || id_marker[k] != S2U(*sbits))
 			errors++;
-		ubits++;
+		sbits++;
 		bits++;
 	}
 
@@ -126,7 +128,7 @@
 	return *n_errors < *n_bits_total / 8;
 }
 
-static bool detect_interleaved_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset,
+static bool detect_interleaved_ahs_id_marker(int *n_errors, int *n_bits_total, const sbit_t *sbits, uint8_t offset,
 					     uint8_t n_bits, const ubit_t * id_marker, uint8_t id_marker_len)
 {
 	unsigned int i, k;
@@ -136,23 +138,23 @@
 	uint8_t remainder = n_bits % id_marker_len;
 
 	/* Override coded in-band data */
-	ubits += offset;
+	sbits += offset;
 
 	/* Check first identification marker bits (23*9 bits) */
 	for (i = 0; i < full_rounds; i++) {
 		for (k = 0; k < id_marker_len; k++) {
-			if (id_marker[k] != *ubits)
+			if (*sbits == 0 || id_marker[k] != S2U(*sbits))
 				errors++;
-			ubits += 2;
+			sbits += 2;
 			bits++;
 		}
 	}
 
 	/* Check remaining identification marker bits (5 bits) */
 	for (k = 0; k < remainder; k++) {
-		if (id_marker[k] != *ubits)
+		if (*sbits == 0 || id_marker[k] != S2U(*sbits))
 			errors++;
-		ubits += 2;
+		sbits += 2;
 		bits++;
 	}
 
@@ -164,125 +166,127 @@
 }
 
 /* Detect an FR AMR SID_FIRST frame by its identifcation marker */
-static bool detect_afs_sid_first(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_afs_sid_first(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 32, 53, id_marker_0, 9);
+	return detect_afs_id_marker(n_errors, n_bits_total, sbits, 32, 53, id_marker_0, 9);
 }
 
 /* Detect an FR AMR SID_UPDATE frame by its identification marker */
-static bool detect_afs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_afs_sid_update(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 36, 53, id_marker_0, 9);
+	return detect_afs_id_marker(n_errors, n_bits_total, sbits, 36, 53, id_marker_0, 9);
 }
 
 /* Detect an FR AMR ONSET frame by its repeating coded inband data */
-static bool detect_afs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static int detect_afs_onset(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
 	bool rc;
 
-	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_1_sid, 16);
+	rc = detect_afs_id_marker(n_errors, n_bits_total, sbits, 4, 57, codec_mode_1_sid, 16);
 	if (rc)
-		return true;
+		return 0;
 
-	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_2_sid, 16);
+	rc = detect_afs_id_marker(n_errors, n_bits_total, sbits, 4, 57, codec_mode_2_sid, 16);
 	if (rc)
-		return true;
+		return 1;
 
-	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_3_sid, 16);
+	rc = detect_afs_id_marker(n_errors, n_bits_total, sbits, 4, 57, codec_mode_3_sid, 16);
 	if (rc)
-		return true;
+		return 2;
 
-	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_4_sid, 16);
+	rc = detect_afs_id_marker(n_errors, n_bits_total, sbits, 4, 57, codec_mode_4_sid, 16);
 	if (rc)
-		return true;
+		return 3;
 
-	return false;
+	return -1;
 }
 
 /* Detect an HR AMR SID UPDATE frame by its identification marker */
-static bool detect_ahs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_ahs_sid_update(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_1);
+	return detect_ahs_id_marker(n_errors, n_bits_total, sbits, id_marker_1);
 }
 
 /* Detect an HR AMR SID FIRST (part 1) frame by its identification marker */
-static bool detect_ahs_sid_first_p1(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_ahs_sid_first_p1(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_0);
+	return detect_ahs_id_marker(n_errors, n_bits_total, sbits, id_marker_0);
 }
 
 /* Detect an HR AMR SID FIRST (part 2) frame by its repeating coded inband data */
-static bool detect_ahs_sid_first_p2(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static int detect_ahs_sid_first_p2(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
 	bool rc;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_1_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 0, 114, codec_mode_1_sid, 16);
 	if (rc)
-		return true;
+		return 0;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_2_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 0, 114, codec_mode_2_sid, 16);
 	if (rc)
-		return true;
+		return 1;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_3_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 0, 114, codec_mode_3_sid, 16);
 	if (rc)
-		return true;
+		return 2;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_4_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 0, 114, codec_mode_4_sid, 16);
 	if (rc)
-		return true;
+		return 3;
 
-	return false;
+	return -1;
 }
 
 /* Detect an HR AMR ONSET frame by its repeating coded inband data */
-static bool detect_ahs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static int detect_ahs_onset(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
 	bool rc;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_1_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 1, 114, codec_mode_1_sid, 16);
 	if (rc)
-		return true;
+		return 0;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_2_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 1, 114, codec_mode_2_sid, 16);
 	if (rc)
-		return true;
+		return 1;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_3_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 1, 114, codec_mode_3_sid, 16);
 	if (rc)
-		return true;
+		return 2;
 
-	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_4_sid, 16);
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 1, 114, codec_mode_4_sid, 16);
 	if (rc)
-		return true;
+		return 3;
 
-	return false;
+	return -1;
 }
 
 /* Detect an HR AMR SID FIRST INHIBIT frame by its identification marker */
-static bool detect_ahs_sid_first_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_ahs_sid_first_inh(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_1, 9);
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 33, 212, id_marker_1, 9);
 }
 
 /* Detect an HR AMR SID UPDATE INHIBIT frame by its identification marker */
-static bool detect_ahs_sid_update_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+static bool detect_ahs_sid_update_inh(int *n_errors, int *n_bits_total, const sbit_t *sbits)
 {
-	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_0, 9);
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, sbits, 33, 212, id_marker_0, 9);
 }
 
 /*! Detect FR AMR DTX frame in unmapped, deinterleaved frame bits.
- *  \param[in] ubits input bits (456 bit).
  *  \param[out] n_errors number of errornous bits.
  *  \param[out] n_bits_total number of checked bits.
+ *  \param[out] mode_id codec mode ID (0..3 or -1).
+ *  \param[in] sbits input soft-bits (456 bit).
  *  \returns dtx frame type. */
-enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame2(int *n_errors, int *n_bits_total,
+							  int *mode_id, const sbit_t *sbits)
 {
-	if (detect_afs_sid_first(n_errors, n_bits_total, ubits))
+	if (detect_afs_sid_first(n_errors, n_bits_total, sbits))
 		return AFS_SID_FIRST;
-	if (detect_afs_sid_update(n_errors, n_bits_total, ubits))
+	if (detect_afs_sid_update(n_errors, n_bits_total, sbits))
 		return AFS_SID_UPDATE;
-	if (detect_afs_onset(n_errors, n_bits_total, ubits))
+	if ((*mode_id = detect_afs_onset(n_errors, n_bits_total, sbits)) != -1)
 		return AFS_ONSET;
 
 	*n_errors = 0;
@@ -290,27 +294,62 @@
 	return AMR_OTHER;
 }
 
-/*! Detect HR AMR DTX frame in unmapped, deinterleaved frame bits.
- *  \param[in] ubits input bits (456 bit).
+/*! Detect FR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  DEPRECATED: use gsm0503_detect_afs_dtx_frame2() instead.
  *  \param[out] n_errors number of errornous bits.
  *  \param[out] n_bits_total number of checked bits.
- *  \returns dtx frame type, */
-enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+ *  \param[in] ubits input bits (456 bit).
+ *  \returns dtx frame type. */
+enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame(int *n_errors, int *n_bits_total,
+							 const ubit_t *ubits)
 {
-	if (detect_ahs_sid_update(n_errors, n_bits_total, ubits))
+	int mode_id; /* unused */
+	sbit_t sbits[456];
+
+	osmo_ubit2sbit(&sbits[0], &ubits[0], sizeof(sbits));
+	return gsm0503_detect_afs_dtx_frame2(n_errors, n_bits_total, &mode_id, &sbits[0]);
+}
+
+/*! Detect HR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \param[out] mode_id codec ID (CMI or CMC/CMR).
+ *  \param[out] mode_id codec mode ID (0..3 or -1).
+ *  \param[in] sbits input soft-bits (456 bit).
+ *  \returns dtx frame type, */
+enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame2(int *n_errors, int *n_bits_total,
+							  int *mode_id, const sbit_t *sbits)
+{
+	if (detect_ahs_sid_update(n_errors, n_bits_total, sbits))
 		return AHS_SID_UPDATE;
-	if (detect_ahs_sid_first_inh(n_errors, n_bits_total, ubits))
+	if (detect_ahs_sid_first_inh(n_errors, n_bits_total, sbits))
 		return AHS_SID_FIRST_INH;
-	if (detect_ahs_sid_update_inh(n_errors, n_bits_total, ubits))
+	if (detect_ahs_sid_update_inh(n_errors, n_bits_total, sbits))
 		return AHS_SID_UPDATE_INH;
-	if (detect_ahs_sid_first_p1(n_errors, n_bits_total, ubits))
+	if (detect_ahs_sid_first_p1(n_errors, n_bits_total, sbits))
 		return AHS_SID_FIRST_P1;
-	if (detect_ahs_sid_first_p2(n_errors, n_bits_total, ubits))
+	if ((*mode_id = detect_ahs_sid_first_p2(n_errors, n_bits_total, sbits)) != -1)
 		return AHS_SID_FIRST_P2;
-	if (detect_ahs_onset(n_errors, n_bits_total, ubits))
+	if ((*mode_id = detect_ahs_onset(n_errors, n_bits_total, sbits)) != -1)
 		return AHS_ONSET;
 
 	*n_errors = 0;
 	*n_bits_total = 0;
 	return AMR_OTHER;
 }
+
+/*! Detect HR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  DEPRECATED: use gsm0503_detect_ahs_dtx_frame2() instead.
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \param[in] ubits input bits (456 bit).
+ *  \returns dtx frame type, */
+enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame(int *n_errors, int *n_bits_total,
+							 const ubit_t *ubits)
+{
+	int mode_id; /* unused */
+	sbit_t sbits[456];
+
+	osmo_ubit2sbit(&sbits[0], &ubits[0], sizeof(sbits));
+	return gsm0503_detect_ahs_dtx_frame2(n_errors, n_bits_total, &mode_id, &sbits[0]);
+}