[FFmpeg-cvslog] Adaptive gain control
Vladimir Voroshilov
git at videolan.org
Sat Sep 24 21:17:04 CEST 2011
ffmpeg | branch: master | Vladimir Voroshilov <voroshil at gmail.com> | Sun Jun 28 21:01:23 2009 +0700| [682337672cd38b8e85acf11578a5130fa87ea1d7] | committer: Michael Niedermayer
Adaptive gain control
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=682337672cd38b8e85acf11578a5130fa87ea1d7
---
libavcodec/g729dec.c | 21 ++++++++++++++++++
libavcodec/g729postfilter.c | 48 +++++++++++++++++++++++++++++++++++++++++++
libavcodec/g729postfilter.h | 20 +++++++++++++++++
3 files changed, 89 insertions(+), 0 deletions(-)
diff --git a/libavcodec/g729dec.c b/libavcodec/g729dec.c
index bc7fbc1..e977e53 100644
--- a/libavcodec/g729dec.c
+++ b/libavcodec/g729dec.c
@@ -145,6 +145,7 @@ typedef struct {
int16_t onset; ///< detected onset level (0-2)
int16_t was_periodic; ///< whether previous frame was declared as periodic or not (4.4)
int16_t ht_prev_data; ///< previous data for 4.2.3, equation 86
+ int gain_coeff; ///< (1.14) gain coefficient (4.2.4)
uint16_t rand_value; ///< random number generator value (4.4.4)
int ma_predictor_prev; ///< switched MA predictor of LSP quantizer from last good frame
@@ -348,6 +349,8 @@ static av_cold int decoder_init(AVCodecContext * avctx)
/* Both 8kbit/s and 6.4kbit/s modes uses two subframes per frame. */
avctx->frame_size = SUBFRAME_SIZE << 1;
+ ctx->gain_coeff = 16384; // 1.0 in (1.14)
+
for (k = 0; k < MA_NP + 1; k++) {
ctx->past_quantizer_outputs[k] = ctx->past_quantizer_output_buf[k];
for (i = 1; i < 11; i++)
@@ -397,6 +400,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size,
int16_t fc[SUBFRAME_SIZE]; // fixed-codebook vector
int16_t synth[SUBFRAME_SIZE+10]; // fixed-codebook vector
int j;
+ int gain_before, gain_after;
int is_periodic = 0; // whether one of the subframes is declared as periodic or not
if (*data_size < SUBFRAME_SIZE << 2) {
@@ -637,6 +641,11 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size,
/* Save data (without postfilter) for use in next subframe. */
memcpy(ctx->syn_filter_data, synth+SUBFRAME_SIZE, 10 * sizeof(int16_t));
+ /* Calculate gain of unfiltered signal for use in AGC. */
+ gain_before = 0;
+ for (j = 0; j < SUBFRAME_SIZE; j++)
+ gain_before += FFABS(synth[j+10]);
+
/* Call postfilter and also update voicing decision for use in next frame. */
g729_postfilter(
&ctx->dsp,
@@ -650,6 +659,18 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size,
synth+10,
SUBFRAME_SIZE);
+ /* Calculate gain of filtered signal for use in AGC. */
+ gain_after = 0;
+ for(j=0; j<SUBFRAME_SIZE; j++)
+ gain_after += FFABS(synth[j+10]);
+
+ ctx->gain_coeff = g729_adaptive_gain_control(
+ gain_before,
+ gain_after,
+ synth+10,
+ SUBFRAME_SIZE,
+ ctx->gain_coeff);
+
if (frame_erasure)
ctx->pitch_delay_int_prev = FFMIN(ctx->pitch_delay_int_prev + 1, PITCH_DELAY_MAX);
else
diff --git a/libavcodec/g729postfilter.c b/libavcodec/g729postfilter.c
index 9af6014..971c3d2 100644
--- a/libavcodec/g729postfilter.c
+++ b/libavcodec/g729postfilter.c
@@ -560,3 +560,51 @@ void g729_postfilter(DSPContext *dsp, int16_t* ht_prev_data, int16_t* voicing,
*ht_prev_data = apply_tilt_comp(speech, pos_filter_data + 10, tilt_comp_coeff,
subframe_size, *ht_prev_data);
}
+
+/**
+ * \brief Adaptive gain control (4.2.4)
+ * \param gain_before gain of speech before applying postfilters
+ * \param gain_after gain of speech after applying postfilters
+ * \param speech [in/out] signal buffer
+ * \param subframe_size length of subframe
+ * \param gain_prev (3.12) previous value of gain coefficient
+ *
+ * \return (3.12) last value of gain coefficient
+ */
+int16_t g729_adaptive_gain_control(int gain_before, int gain_after, int16_t *speech,
+ int subframe_size, int16_t gain_prev)
+{
+ int gain; // (3.12)
+ int n;
+ int exp_before, exp_after;
+
+ if(!gain_after && gain_before)
+ return 0;
+
+ if (gain_before) {
+
+ exp_before = 14 - av_log2(gain_before);
+ gain_before = bidir_sal(gain_before, exp_before);
+
+ exp_after = 14 - av_log2(gain_after);
+ gain_after = bidir_sal(gain_after, exp_after);
+
+ if (gain_before < gain_after) {
+ gain = (gain_before << 15) / gain_after;
+ gain = bidir_sal(gain, exp_after - exp_before - 1);
+ } else {
+ gain = ((gain_before - gain_after) << 14) / gain_after + 0x4000;
+ gain = bidir_sal(gain, exp_after - exp_before);
+ }
+ gain = (gain * G729_AGC_FAC1 + 0x4000) >> 15; // gain * (1-0.9875)
+ } else
+ gain = 0;
+
+ for (n = 0; n < subframe_size; n++) {
+ // gain_prev = gain + 0.9875 * gain_prev
+ gain_prev = (G729_AGC_FACTOR * gain_prev + 0x4000) >> 15;
+ gain_prev = av_clip_int16(gain + gain_prev);
+ speech[n] = av_clip_int16((speech[n] * gain_prev + 0x2000) >> 14);
+ }
+ return gain_prev;
+}
diff --git a/libavcodec/g729postfilter.h b/libavcodec/g729postfilter.h
index 0766799..956cde9 100644
--- a/libavcodec/g729postfilter.h
+++ b/libavcodec/g729postfilter.h
@@ -40,6 +40,13 @@
#define FORMANT_PP_FACTOR_DEN 22938 //0.70 in Q15
/**
+ * gain adjustment factor (G.729, 4.2.4)
+ * 0.9875 in Q15
+ */
+#define G729_AGC_FACTOR 32358
+#define G729_AGC_FAC1 (32768-G729_AGC_FACTOR)
+
+/**
* 1.0 / (1.0 + 0.5) in Q15
* where 0.5 is the minimum value of
* weight factor, controlling amount of long-term postfiltering
@@ -92,4 +99,17 @@ void g729_postfilter(DSPContext *dsp, int16_t* ht_prev_data, int16_t* voicing,
int16_t* pos_filter_data, int16_t *speech,
int subframe_size);
+/**
+ * \brief Adaptive gain control (4.2.4)
+ * \param gain_before (Q0) gain of speech before applying postfilters
+ * \param gain_after (Q0) gain of speech after applying postfilters
+ * \param speech [in/out] (Q0) signal buffer
+ * \param subframe_size length of subframe
+ * \param gain_prev (Q12) previous value of gain coefficient
+ *
+ * \return (Q12) last value of gain coefficient
+ */
+int16_t g729_adaptive_gain_control(int gain_before, int gain_after, int16_t *speech,
+ int subframe_size, int16_t gain_prev);
+
#endif // FFMPEG_G729POSTFILTER_H
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