Author: cmcq
Date: Thu Jul 23 16:04:58 2009
New Revision: 4789
Log:
Cosmetics: rename apply_ir_filter to anti_sparseness and clarify the name
Modified:
amr/amrnbfloatdec.c
Modified: amr/amrnbfloatdec.c
==============================================================================
--- amr/amrnbfloatdec.c Thu Jul 23 15:03:18 2009 (r4788)
+++ amr/amrnbfloatdec.c Thu Jul 23 16:04:58 2009 (r4789)
@@ -75,7 +75,7 @@ typedef struct AMRContext {
int diff_count; ///< the number of subframes for
which diff has been above 0.65
int hang_count; ///< the number of subframes
since a hangover period started
- float prev_ir_fixed_gain; ///< previous fixed gain used by
impulse response filter
+ float prev_sparse_fixed_gain; ///< previous fixed gain; used by
anti-sparseness processing to determine "onset"
uint8_t prev_ir_filter_strength; ///< previous impulse response
filter strength; 0 - strong, 1 - medium, 2 - none
uint8_t ir_filter_onset; ///< flag for impulse response
filter strength
@@ -826,17 +826,23 @@ static void decode_gains(AMRContext *p,
/// @{
/**
- * adaptive phase dispersion; forming of total excitation
+ * Reduce fixed vector sparseness by smoothing with one of three IR filters.
+ *
+ * This implements 3GPP TS 26.090 section 6.1(5).
+ *
+ * In the patent description "Method and device for coding speech in
+ * analysis-by-synthesis speech coders" by Ari P. Heikkinen, this method
+ * is called "adaptive phase dispersion". This name is also used in the
+ * reference source, but not in the spec.
*
* @param p the context
* @param fixed_vector algebraic codebook vector
* @param fixed_gain smoothed gain
*/
-static void apply_ir_filter(AMRContext *p, float *fixed_vector, float
fixed_gain)
+static void anti_sparseness(AMRContext *p, float *fixed_vector, float
fixed_gain)
{
int ir_filter_strength;
- // anti-sparseness processing
if (p->pitch_gain[4] < 0.6) {
// strong filtering
ir_filter_strength = 0;
@@ -849,7 +855,7 @@ static void apply_ir_filter(AMRContext *
}
// detect 'onset'
- if (fixed_gain > 2.0 * p->prev_ir_fixed_gain) {
+ if (fixed_gain > 2.0 * p->prev_sparse_fixed_gain) {
p->ir_filter_onset = 2;
} else if (p->ir_filter_onset) {
p->ir_filter_onset--;
@@ -886,7 +892,7 @@ static void apply_ir_filter(AMRContext *
// update ir filter strength history
p->prev_ir_filter_strength = ir_filter_strength;
- p->prev_ir_fixed_gain = fixed_gain;
+ p->prev_sparse_fixed_gain = fixed_gain;
}
/// @}
@@ -1175,7 +1181,7 @@ static int amrnb_decode_frame(AVCodecCon
synth_fixed_gain = fixed_gain_smooth(p, p->lsf_q[subframe],
p->lsf_avg, p->cur_frame_mode);
- apply_ir_filter(p, p->fixed_vector, synth_fixed_gain);
+ anti_sparseness(p, p->fixed_vector, synth_fixed_gain);
/*** end of pre-processing ***/
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