From 33f18a20dc1eb401e51369e97674f09f79943631 Mon Sep 17 00:00:00 2001
From: Felicia Lim <flim@google.com>
Date: Mon, 16 May 2016 15:52:44 +0200
Subject: [PATCH] Turn on DTX only when the noise is sufficiently quiet
Computes a pseudo SNR as the ratio between the running peak signal
energy to instantaneous noise energy. DTX is turned on only if this is
higher than a pre-determined threshold.
Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
---
src/opus_encoder.c | 55 +++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 52 insertions(+), 3 deletions(-)
diff --git a/src/opus_encoder.c b/src/opus_encoder.c
index d62ea3f73..671e8d210 100644
--- a/src/opus_encoder.c
+++ b/src/opus_encoder.c
@@ -53,6 +53,10 @@
#define MAX_ENCODER_BUFFER 480
+#ifndef DISABLE_FLOAT_API
+#define PSEUDO_SNR_THRESHOLD 316.23f /* 10^(25/10) */
+#endif
+
typedef struct {
opus_val32 XX, XY, YY;
opus_val16 smoothed_width;
@@ -107,6 +111,7 @@ struct OpusEncoder {
#ifndef DISABLE_FLOAT_API
int detected_bandwidth;
int nb_no_activity_frames;
+ opus_val32 peak_signal_energy;
#endif
opus_uint32 rangeFinal;
};
@@ -1028,20 +1033,60 @@ static int is_digital_silence(const opus_val16* pcm, int frame_size, int lsb_dep
return silence;
}
+static opus_val32 compute_frame_energy(const opus_val16 *pcm, int frame_size)
+{
+ int i;
+#ifdef FIXED_POINT
+ opus_val32 sample_max;
+ int max_shift;
+ int shift;
+#endif
+ opus_val32 energy = 0;
+
+#ifdef FIXED_POINT
+ /* Max amplitude in the signal */
+ sample_max = celt_maxabs16(pcm, frame_size);
+
+ /* Compute the right shift required in the MAC to avoid an overflow */
+ max_shift = celt_ilog2(frame_size);
+ shift = IMAX(0, (celt_ilog2(sample_max) << 1) + max_shift - 28);
+#endif
+
+ /* Compute the energy */
+ for (i=0; i<frame_size; i++)
+ energy += SHR32(MULT16_16(pcm[i], pcm[i]), shift);
+
+ /* Normalize energy by the frame size and left-shift back to the original position */
+ energy /= frame_size;
+ energy = SHL32(energy, shift);
+
+ return energy;
+}
+
/* Decides if DTX should be turned on (=1) or off (=0) */
static int decide_dtx_mode(float activity_probability, /* probability that current frame contains speech/music */
int *nb_no_activity_frames, /* number of consecutive frames with no activity */
+ opus_val32 peak_signal_energy, /* peak energy of desired signal detected so far */
+ const opus_val16 *pcm, /* input pcm signal */
+ int frame_size, /* frame size */
int is_silence /* only digital silence detected in this frame */
)
{
- int is_noise = 0;
+ int is_noise;
+ opus_val32 noise_energy;
+ int is_sufficiently_quiet;
if (!is_silence)
{
is_noise = activity_probability < DTX_ACTIVITY_THRESHOLD;
+ if (is_noise)
+ {
+ noise_energy = compute_frame_energy(pcm, frame_size);
+ is_sufficiently_quiet = peak_signal_energy >= (PSEUDO_SNR_THRESHOLD * noise_energy);
+ }
}
- if (is_silence || is_noise)
+ if (is_silence || (is_noise && is_sufficiently_quiet))
{
/* The number of consecutive DTX frames should be within the allowed bounds */
(*nb_no_activity_frames)++;
@@ -1145,6 +1190,10 @@ opus_int32 opus_encode_native(OpusEncoder *st, const opus_val16 *pcm, int frame_
c1, c2, analysis_channels, st->Fs,
lsb_depth, downmix, &analysis_info);
}
+
+ /* Track the peak signal energy */
+ if (!is_silence && analysis_info.activity_probability > DTX_ACTIVITY_THRESHOLD)
+ st->peak_signal_energy = MAX32(MULT16_32_Q15(QCONST16(0.999, 15), st->peak_signal_energy), compute_frame_energy(pcm, frame_size));
}
#else
(void)analysis_pcm;
@@ -2095,7 +2144,7 @@ opus_int32 opus_encode_native(OpusEncoder *st, const opus_val16 *pcm, int frame_
#ifndef DISABLE_FLOAT_API
if (st->use_dtx && (analysis_info.valid || is_silence))
{
- if (decide_dtx_mode(analysis_info.activity_probability, &st->nb_no_activity_frames, is_silence))
+ if (decide_dtx_mode(analysis_info.activity_probability, &st->nb_no_activity_frames, st->peak_signal_energy, pcm, frame_size, is_silence))
{
st->rangeFinal = 0;
data[0] = gen_toc(st->mode, st->Fs/frame_size, curr_bandwidth, st->stream_channels);
--
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