From 480ba7034810fec56625dcd9ceeeb01d75c8d755 Mon Sep 17 00:00:00 2001
From: Koen Vos <koen.vos@skype.net>
Date: Wed, 5 Oct 2011 13:49:54 -0400
Subject: [PATCH] SILK stereo fix
Fixes a mono-stereo switching glitch and fixes a side prediction
bug where coding side would result in worse panned-mono behaviour
---
silk/stereo_LR_to_MS.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/silk/stereo_LR_to_MS.c b/silk/stereo_LR_to_MS.c
index 7c4b7c1d3..5f3eee577 100644
--- a/silk/stereo_LR_to_MS.c
+++ b/silk/stereo_LR_to_MS.c
@@ -96,8 +96,9 @@ void silk_stereo_LR_to_MS(
/* Determine bitrate distribution between mid and side, and possibly reduce stereo width */
total_rate_bps -= is10msFrame ? 1200 : 600; /* Subtract approximate bitrate for coding stereo parameters */
- if (total_rate_bps < 1)
+ if (total_rate_bps < 1 ) {
total_rate_bps = 1;
+ }
min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 900 );
silk_assert( min_mid_rate_bps < 32767 );
/* Default bitrate distribution: 8 parts for Mid and (5+3*frac) parts for Side. so: mid_rate = ( 8 / ( 13 + 3 * frac ) ) * total_ rate */
@@ -119,26 +120,44 @@ void silk_stereo_LR_to_MS(
/* Smoother */
state->smth_width_Q14 = (opus_int16)silk_SMLAWB( state->smth_width_Q14, width_Q14 - state->smth_width_Q14, smooth_coef_Q16 );
- /* Reduce predictors */
- pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
- pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
-
+ /* At very low bitrates or for inputs that are nearly amplitude panned, switch to panned-mono coding */
*mid_only_flag = 0;
if( state->width_prev_Q14 == 0 &&
( 8 * total_rate_bps < 13 * min_mid_rate_bps || silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.05, 14 ) ) )
{
+ /* Code as panned-mono; previous frame already had zero width */
+ /* Scale down and quantize predictors */
+ pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
+ pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
+ silk_stereo_quant_pred( pred_Q13, ix );
+ /* Collapse stereo width */
width_Q14 = 0;
- /* Only encode mid channel */
+ pred_Q13[ 0 ] = 0;
+ pred_Q13[ 1 ] = 0;
mid_side_rates_bps[ 0 ] = total_rate_bps;
mid_side_rates_bps[ 1 ] = 0;
*mid_only_flag = 1;
} else if( state->width_prev_Q14 != 0 &&
( 8 * total_rate_bps < 11 * min_mid_rate_bps || silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.02, 14 ) ) )
{
+ /* Transition to zero-width stereo */
+ /* Scale down and quantize predictors */
+ pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
+ pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
+ silk_stereo_quant_pred( pred_Q13, ix );
+ /* Collapse stereo width */
width_Q14 = 0;
+ pred_Q13[ 0 ] = 0;
+ pred_Q13[ 1 ] = 0;
} else if( state->smth_width_Q14 > SILK_FIX_CONST( 0.95, 14 ) ) {
+ /* Full-width stereo coding */
+ silk_stereo_quant_pred( pred_Q13, ix );
width_Q14 = SILK_FIX_CONST( 1, 14 );
} else {
+ /* Reduced-width stereo coding; scale down and quantize predictors */
+ pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
+ pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
+ silk_stereo_quant_pred( pred_Q13, ix );
width_Q14 = state->smth_width_Q14;
}
@@ -149,9 +168,6 @@ void silk_stereo_LR_to_MS(
DEBUG_STORE_DATA( width.pcm, &width_Q14, 4 );
#endif
- /* Quantize predictors */
- silk_stereo_quant_pred( pred_Q13, ix );
-
/* Interpolate predictors and subtract prediction from side channel */
pred0_Q13 = -state->pred_prev_Q13[ 0 ];
pred1_Q13 = -state->pred_prev_Q13[ 1 ];
@@ -169,6 +185,7 @@ void silk_stereo_LR_to_MS(
sum = silk_SMLAWB( sum, silk_LSHIFT( ( opus_int32 )mid[ n + 1 ], 11 ), pred1_Q13 ); /* Q8 */
x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
}
+
pred0_Q13 = -pred_Q13[ 0 ];
pred1_Q13 = -pred_Q13[ 1 ];
w_Q24 = silk_LSHIFT( width_Q14, 10 );
--
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