AMR narrowband decoder. More...

#include <string.h>
#include <math.h>
#include "libavutil/channel_layout.h"
#include "libavutil/float_dsp.h"
#include "avcodec.h"
#include "libavutil/common.h"
#include "libavutil/avassert.h"
#include "celp_math.h"
#include "celp_filters.h"
#include "acelp_filters.h"
#include "acelp_vectors.h"
#include "acelp_pitch_delay.h"
#include "lsp.h"
#include "amr.h"
#include "internal.h"
#include "amrnbdata.h"

Data Structures
struct	AMRContext

Macros
#define	AMR_BLOCK_SIZE 160
	samples per frame More...

#define	AMR_SAMPLE_BOUND 32768.0
	threshold for synthesis overflow More...

#define	AMR_SAMPLE_SCALE (2.0 / 32768.0)
	Scale from constructed speech to [-1,1]. More...

#define	PRED_FAC_MODE_12k2 0.65
	Prediction factor for 12.2kbit/s mode. More...

#define	LSF_R_FAC (8000.0 / 32768.0)
	LSF residual tables to Hertz. More...

#define	MIN_LSF_SPACING (50.0488 / 8000.0)
	Ensures stability of LPC filter. More...

#define	PITCH_LAG_MIN_MODE_12k2 18
	Lower bound on decoded lag search in 12.2kbit/s mode. More...

#define	MIN_ENERGY -14.0
	Initial energy in dB. More...

#define	SHARP_MAX 0.79449462890625
	Maximum sharpening factor. More...

#define	AMR_TILT_RESPONSE 22
	Number of impulse response coefficients used for tilt factor. More...

#define	AMR_TILT_GAMMA_T 0.8
	Tilt factor = 1st reflection coefficient * gamma_t. More...

#define	AMR_AGC_ALPHA 0.9
	Adaptive gain control factor used in post-filter. More...

Functions
static void	weighted_vector_sumd (double out, const double in_a, const double *in_b, double weight_coeff_a, double weight_coeff_b, int length)
	Double version of ff_weighted_vector_sumf() More...

static av_cold int	amrnb_decode_init (AVCodecContext *avctx)

static enum Mode	unpack_bitstream (AMRContext p, const uint8_t buf, int buf_size)
	Unpack an RFC4867 speech frame into the AMR frame mode and parameters. More...

static int	amrnb_decode_frame (AVCodecContext avctx, void data, int got_frame_ptr, AVPacket avpkt)

AMR pitch LPC coefficient decoding functions
static void	interpolate_lsf (ACELPVContext ctx, float lsf_q[4][LP_FILTER_ORDER], float lsf_new)
	Interpolate the LSF vector (used for fixed gain smoothing). More...

static void	lsf2lsp_for_mode12k2 (AMRContext p, double lsp[LP_FILTER_ORDER], const float lsf_no_r[LP_FILTER_ORDER], const int16_t lsf_quantizer[5], const int quantizer_offset, const int sign, const int update)
	Decode a set of 5 split-matrix quantized lsf indexes into an lsp vector. More...

static void	lsf2lsp_5 (AMRContext *p)
	Decode a set of 5 split-matrix quantized lsf indexes into 2 lsp vectors. More...

static void	lsf2lsp_3 (AMRContext *p)
	Decode a set of 3 split-matrix quantized lsf indexes into an lsp vector. More...

AMR pitch vector decoding functions
static void	decode_pitch_lag_1_6 (int lag_int, int lag_frac, int pitch_index, const int prev_lag_int, const int subframe)
	Like ff_decode_pitch_lag(), but with 1/6 resolution. More...

static void	decode_pitch_vector (AMRContext p, const AMRNBSubframe amr_subframe, const int subframe)

AMR algebraic code book (fixed) vector decoding functions
static void	decode_10bit_pulse (int code, int pulse_position[8], int i1, int i2, int i3)
	Decode a 10-bit algebraic codebook index from a 10.2 kbit/s frame. More...

static void	decode_8_pulses_31bits (const int16_t fixed_index, AMRFixed fixed_sparse)
	Decode the algebraic codebook index to pulse positions and signs and construct the algebraic codebook vector for MODE_10k2. More...

static void	decode_fixed_sparse (AMRFixed fixed_sparse, const uint16_t pulses, const enum Mode mode, const int subframe)
	Decode the algebraic codebook index to pulse positions and signs, then construct the algebraic codebook vector. More...

static void	pitch_sharpening (AMRContext p, int subframe, enum Mode mode, AMRFixed fixed_sparse)
	Apply pitch lag to obtain the sharpened fixed vector (section 6.1.2) More...

AMR gain decoding functions
static float	fixed_gain_smooth (AMRContext p, const float lsf, const float *lsf_avg, const enum Mode mode)
	fixed gain smoothing Note that where the spec specifies the "spectrum in the q domain" in section 6.1.4, in fact frequencies should be used. More...

static void	decode_gains (AMRContext p, const AMRNBSubframe amr_subframe, const enum Mode mode, const int subframe, float *fixed_gain_factor)
	Decode pitch gain and fixed gain factor (part of section 6.1.3). More...

AMR preprocessing functions
static void	apply_ir_filter (float out, const AMRFixed in, const float *filter)
	Circularly convolve a sparse fixed vector with a phase dispersion impulse response filter (D.6.2 of G.729 and 6.1.5 of AMR). More...

static const float *	anti_sparseness (AMRContext p, AMRFixed fixed_sparse, const float fixed_vector, float fixed_gain, float out)
	Reduce fixed vector sparseness by smoothing with one of three IR filters. More...

AMR synthesis functions
static int	synthesis (AMRContext p, float lpc, float fixed_gain, const float fixed_vector, float samples, uint8_t overflow)
	Conduct 10th order linear predictive coding synthesis. More...

AMR update functions
static void	update_state (AMRContext *p)
	Update buffers and history at the end of decoding a subframe. More...

AMR Postprocessing functions
static float	tilt_factor (AMRContext p, float lpc_n, float *lpc_d)
	Get the tilt factor of a formant filter from its transfer function. More...

static void	postfilter (AMRContext p, float lpc, float *buf_out)
	Perform adaptive post-filtering to enhance the quality of the speech. More...

Variables
AVCodec	ff_amrnb_decoder

Detailed Description

AMR narrowband decoder.

This decoder uses floats for simplicity and so is not bit-exact. One difference is that differences in phase can accumulate. The test sequences in 3GPP TS 26.074 can still be useful.

Comparing this file's output to the output of the ref decoder gives a PSNR of 30 to 80. Plotting the output samples shows a difference in phase in some areas.
Comparing both decoders against their input, this decoder gives a similar PSNR. If the test sequence homing frames are removed (this decoder does not detect them), the PSNR is at least as good as the reference on 140 out of 169 tests.

Definition in file amrnbdec.c.

Macro Definition Documentation

◆ AMR_BLOCK_SIZE

#define AMR_BLOCK_SIZE 160

samples per frame

Definition at line 62 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ AMR_SAMPLE_BOUND

#define AMR_SAMPLE_BOUND 32768.0

threshold for synthesis overflow

Definition at line 63 of file amrnbdec.c.

Referenced by synthesis().

◆ AMR_SAMPLE_SCALE

#define AMR_SAMPLE_SCALE (2.0 / 32768.0)

Scale from constructed speech to [-1,1].

AMR is designed to produce 16-bit PCM samples (3GPP TS 26.090 4.2) but upscales by two (section 6.2.2).

Fundamentally, this scale is determined by energy_mean through the fixed vector contribution to the excitation vector.

Definition at line 74 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ PRED_FAC_MODE_12k2

#define PRED_FAC_MODE_12k2 0.65

Prediction factor for 12.2kbit/s mode.

Definition at line 77 of file amrnbdec.c.

Referenced by lsf2lsp_5().

◆ LSF_R_FAC

#define LSF_R_FAC (8000.0 / 32768.0)

LSF residual tables to Hertz.

Definition at line 79 of file amrnbdec.c.

Referenced by lsf2lsp_3(), lsf2lsp_5(), and lsf2lsp_for_mode12k2().

◆ MIN_LSF_SPACING

#define MIN_LSF_SPACING (50.0488 / 8000.0)

Ensures stability of LPC filter.

Definition at line 80 of file amrnbdec.c.

Referenced by lsf2lsp_3(), and lsf2lsp_for_mode12k2().

◆ PITCH_LAG_MIN_MODE_12k2

#define PITCH_LAG_MIN_MODE_12k2 18

Lower bound on decoded lag search in 12.2kbit/s mode.

Definition at line 81 of file amrnbdec.c.

Referenced by decode_pitch_lag_1_6().

◆ MIN_ENERGY

#define MIN_ENERGY -14.0

Initial energy in dB.

Also used for bad frames (unimplemented).

Definition at line 84 of file amrnbdec.c.

Referenced by amrnb_decode_init(), and amrwb_decode_init().

◆ SHARP_MAX

#define SHARP_MAX 0.79449462890625

Maximum sharpening factor.

The specification says 0.8, which should be 13107, but the reference C code uses 13017 instead. (Amusingly the same applies to SHARP_MAX in g729dec.c.)

Definition at line 91 of file amrnbdec.c.

Referenced by pitch_sharpening(), and synthesis().

◆ AMR_TILT_RESPONSE

#define AMR_TILT_RESPONSE 22

Number of impulse response coefficients used for tilt factor.

Definition at line 94 of file amrnbdec.c.

Referenced by tilt_factor().

◆ AMR_TILT_GAMMA_T

#define AMR_TILT_GAMMA_T 0.8

Tilt factor = 1st reflection coefficient * gamma_t.

Definition at line 96 of file amrnbdec.c.

Referenced by tilt_factor().

◆ AMR_AGC_ALPHA

#define AMR_AGC_ALPHA 0.9

Adaptive gain control factor used in post-filter.

Definition at line 98 of file amrnbdec.c.

Referenced by postfilter().

Function Documentation

◆ weighted_vector_sumd()

static void weighted_vector_sumd	(	double *	out,
		const double *	in_a,
		const double *	in_b,
		double	weight_coeff_a,
		double	weight_coeff_b,
		int	length
	)

static

Double version of ff_weighted_vector_sumf()

Definition at line 149 of file amrnbdec.c.

Referenced by lsf2lsp_5().

◆ amrnb_decode_init()

static av_cold int amrnb_decode_init ( AVCodecContext * avctx )

static

Definition at line 160 of file amrnbdec.c.

◆ unpack_bitstream()

static enum Mode unpack_bitstream	(	AMRContext *	p,
		const uint8_t *	buf,
		int	buf_size
	)

static

Unpack an RFC4867 speech frame into the AMR frame mode and parameters.

The order of speech bits is specified by 3GPP TS 26.101.

Parameters

p	the context
buf	pointer to the input buffer
buf_size	size of the input buffer

Returns: the frame mode

Definition at line 207 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ interpolate_lsf()

static void interpolate_lsf	(	ACELPVContext *	ctx,
		float	lsf_q[4][LP_FILTER_ORDER],
		float *	lsf_new
	)

static

Interpolate the LSF vector (used for fixed gain smoothing).

The interpolation is done over all four subframes even in MODE_12k2.

Parameters

[in]	ctx	The Context
[in,out]	lsf_q	LSFs in [0,1] for each subframe
[in]	lsf_new	New LSFs in [0,1] for subframe 4

Definition at line 239 of file amrnbdec.c.

Referenced by lsf2lsp_3(), and lsf2lsp_for_mode12k2().

◆ lsf2lsp_for_mode12k2()

static void lsf2lsp_for_mode12k2	(	AMRContext *	p,
		double	lsp[LP_FILTER_ORDER],
		const float	lsf_no_r[LP_FILTER_ORDER],
		const int16_t *	lsf_quantizer[5],
		const int	quantizer_offset,
		const int	sign,
		const int	update
	)

static

Decode a set of 5 split-matrix quantized lsf indexes into an lsp vector.

Parameters

p	the context
lsp	output LSP vector
lsf_no_r	LSF vector without the residual vector added
lsf_quantizer	pointers to LSF dictionary tables
quantizer_offset	offset in tables
sign	for the 3 dictionary table
update	store data for computing the next frame's LSFs

Definition at line 260 of file amrnbdec.c.

Referenced by lsf2lsp_5().

◆ lsf2lsp_5()

static void lsf2lsp_5 ( AMRContext * p )

static

Decode a set of 5 split-matrix quantized lsf indexes into 2 lsp vectors.

Parameters

p	pointer to the AMRContext

Definition at line 298 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ lsf2lsp_3()

static void lsf2lsp_3 ( AMRContext * p )

static

Decode a set of 3 split-matrix quantized lsf indexes into an lsp vector.

Parameters

p	pointer to the AMRContext

Definition at line 327 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ decode_pitch_lag_1_6()

static void decode_pitch_lag_1_6	(	int *	lag_int,
		int *	lag_frac,
		int	pitch_index,
		const int	prev_lag_int,
		const int	subframe
	)

static

Like ff_decode_pitch_lag(), but with 1/6 resolution.

Definition at line 372 of file amrnbdec.c.

Referenced by decode_pitch_vector().

◆ decode_pitch_vector()

static void decode_pitch_vector	(	AMRContext *	p,
		const AMRNBSubframe *	amr_subframe,
		const int	subframe
	)

static

Definition at line 391 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ decode_10bit_pulse()

static void decode_10bit_pulse	(	int	code,
		int	pulse_position[8],
		int	i1,
		int	i2,
		int	i3
	)

static

Decode a 10-bit algebraic codebook index from a 10.2 kbit/s frame.

Definition at line 435 of file amrnbdec.c.

Referenced by decode_8_pulses_31bits().

◆ decode_8_pulses_31bits()

static void decode_8_pulses_31bits	(	const int16_t *	fixed_index,
		AMRFixed *	fixed_sparse
	)

static

Decode the algebraic codebook index to pulse positions and signs and construct the algebraic codebook vector for MODE_10k2.

Parameters

fixed_index	positions of the eight pulses
fixed_sparse	pointer to the algebraic codebook vector

Definition at line 453 of file amrnbdec.c.

Referenced by decode_fixed_sparse().

◆ decode_fixed_sparse()

static void decode_fixed_sparse	(	AMRFixed *	fixed_sparse,
		const uint16_t *	pulses,
		const enum Mode	mode,
		const int	subframe
	)

static

Decode the algebraic codebook index to pulse positions and signs, then construct the algebraic codebook vector.

Parameters

fixed_sparse	pointer to the algebraic codebook vector
pulses	algebraic codebook indexes
mode	mode of the current frame
subframe	current subframe number

Definition at line 499 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ pitch_sharpening()

static void pitch_sharpening	(	AMRContext *	p,
		int	subframe,
		enum Mode	mode,
		AMRFixed *	fixed_sparse
	)

static

Apply pitch lag to obtain the sharpened fixed vector (section 6.1.2)

Parameters

p	the context
subframe	unpacked amr subframe
mode	mode of the current frame
fixed_sparse	sparse representation of the fixed vector

Definition at line 552 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ fixed_gain_smooth()

static float fixed_gain_smooth	(	AMRContext *	p,
		const float *	lsf,
		const float *	lsf_avg,
		const enum Mode	mode
	)

static

fixed gain smoothing Note that where the spec specifies the "spectrum in the q domain" in section 6.1.4, in fact frequencies should be used.

Parameters

p	the context
lsf	LSFs for the current subframe, in the range [0,1]
lsf_avg	averaged LSFs
mode	mode of the current frame

Returns: fixed gain smoothed

Definition at line 588 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ decode_gains()

static void decode_gains	(	AMRContext *	p,
		const AMRNBSubframe *	amr_subframe,
		const enum Mode	mode,
		const int	subframe,
		float *	fixed_gain_factor
	)

static

Decode pitch gain and fixed gain factor (part of section 6.1.3).

Parameters

p	the context
amr_subframe	unpacked amr subframe
mode	mode of the current frame
subframe	current subframe number
fixed_gain_factor	decoded gain correction factor

Definition at line 630 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ apply_ir_filter()

static void apply_ir_filter	(	float *	out,
		const AMRFixed *	in,
		const float *	filter
	)

static

Circularly convolve a sparse fixed vector with a phase dispersion impulse response filter (D.6.2 of G.729 and 6.1.5 of AMR).

Parameters

out	vector with filter applied
in	source vector
filter	phase filter coefficients

out[n] = sum(i,0,len-1){ in[i] * filter[(len + n - i)len] }

< filters at pitch lag*1 and *2

Definition at line 672 of file amrnbdec.c.

Referenced by anti_sparseness().

◆ anti_sparseness()

static const float* anti_sparseness	(	AMRContext *	p,
		AMRFixed *	fixed_sparse,
		const float *	fixed_vector,
		float	fixed_gain,
		float *	out
	)

static

Reduce fixed vector sparseness by smoothing with one of three IR filters.

Also know as "adaptive phase dispersion".

This implements 3GPP TS 26.090 section 6.1(5).

Parameters

p	the context
fixed_sparse	algebraic codebook vector
fixed_vector	unfiltered fixed vector
fixed_gain	smoothed gain
out	space for modified vector if necessary

Definition at line 719 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ synthesis()

static int synthesis	(	AMRContext *	p,
		float *	lpc,
		float	fixed_gain,
		const float *	fixed_vector,
		float *	samples,
		uint8_t	overflow
	)

static

Conduct 10th order linear predictive coding synthesis.

Parameters

p	pointer to the AMRContext
lpc	pointer to the LPC coefficients
fixed_gain	fixed codebook gain for synthesis
fixed_vector	algebraic codebook vector
samples	pointer to the output speech samples
overflow	16-bit overflow flag

Definition at line 790 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ update_state()

static void update_state ( AMRContext * p )

static

Update buffers and history at the end of decoding a subframe.

Parameters

p	pointer to the AMRContext

Definition at line 847 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ tilt_factor()

static float tilt_factor	(	AMRContext *	p,
		float *	lpc_n,
		float *	lpc_d
	)

static

Get the tilt factor of a formant filter from its transfer function.

Parameters

p	The Context
lpc_n	LP_FILTER_ORDER coefficients of the numerator
lpc_d	LP_FILTER_ORDER coefficients of the denominator

Definition at line 874 of file amrnbdec.c.

Referenced by postfilter().

◆ postfilter()

static void postfilter	(	AMRContext *	p,
		float *	lpc,
		float *	buf_out
	)

static

Perform adaptive post-filtering to enhance the quality of the speech.

See section 6.2.1.

Parameters

p	pointer to the AMRContext
lpc	interpolated LP coefficients for this subframe
buf_out	output of the filter

Definition at line 904 of file amrnbdec.c.

Referenced by amrnb_decode_frame().

◆ amrnb_decode_frame()

static int amrnb_decode_frame	(	AVCodecContext *	avctx,
		void *	data,
		int *	got_frame_ptr,
		AVPacket *	avpkt
	)

static

Definition at line 948 of file amrnbdec.c.

Variable Documentation

◆ ff_amrnb_decoder

AVCodec ff_amrnb_decoder

Initial value:

= {
    .name           = "amrnb",
    .long_name      = NULL_IF_CONFIG_SMALL("AMR-NB (Adaptive Multi-Rate NarrowBand)"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_AMR_NB,
    .priv_data_size = sizeof(AMRContext),
    .init           = amrnb_decode_init,
    .decode         = amrnb_decode_frame,
    .capabilities   = AV_CODEC_CAP_DR1,
    .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_FLT,
                                                     AV_SAMPLE_FMT_NONE },
}

Definition at line 1083 of file amrnbdec.c.

Data Structures

Macros

Functions

Variables

Detailed Description

Macro Definition Documentation

◆ AMR_BLOCK_SIZE

◆ AMR_SAMPLE_BOUND

◆ AMR_SAMPLE_SCALE

◆ PRED_FAC_MODE_12k2

◆ LSF_R_FAC

◆ MIN_LSF_SPACING

◆ PITCH_LAG_MIN_MODE_12k2

◆ MIN_ENERGY

◆ SHARP_MAX

◆ AMR_TILT_RESPONSE

◆ AMR_TILT_GAMMA_T

◆ AMR_AGC_ALPHA

Function Documentation

◆ weighted_vector_sumd()

◆ amrnb_decode_init()

◆ unpack_bitstream()

◆ interpolate_lsf()

◆ lsf2lsp_for_mode12k2()

◆ lsf2lsp_5()

◆ lsf2lsp_3()

◆ decode_pitch_lag_1_6()

◆ decode_pitch_vector()

◆ decode_10bit_pulse()

◆ decode_8_pulses_31bits()

◆ decode_fixed_sparse()

◆ pitch_sharpening()

◆ fixed_gain_smooth()

◆ decode_gains()

◆ apply_ir_filter()

◆ anti_sparseness()

◆ synthesis()

◆ update_state()

◆ tilt_factor()

◆ postfilter()

◆ amrnb_decode_frame()

Variable Documentation

◆ ff_amrnb_decoder