AMR-WB+标准：3GPP协议推动移动网络音频编码新趋势

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AMR-WB+标准，全称为Extended Adaptive Multi-Rate-Wideband (AMR-WB+) 编解码器，是3GPP（Third Generation Partnership Project）组织为移动通信系统制定的一种高级音频编码技术，旨在提供更高质量的语音通信体验，尤其是在第四代移动通信系统（4G）如Long-Term Evolution (LTE) 中。该标准是在ETSITS 126290 V9.0.0（2010年1月发布）的技术规范中详细定义的，适用于数字蜂窝电话系统（Phase 2+）和通用移动通信系统（UMTS）。在3GPP TS 26.290版本9.0.0的Release 9中，AMR-WB+编码器和解码器功能被纳入，这些功能允许在不同网络环境下高效地进行音频信号的编码和传输，从而降低带宽需求，提高通话质量和实时性。AMR-WB+相较于AMR（Adaptive Multi-Rate）和AMR-NB（Adaptive Multi-Rate Narrowband）等早期版本，具有更高的采样率（通常为23.05 kHz），能提供清晰度更高的语音，适合于那些对音质有较高要求的应用场景。 AMR-WB+支持编码和解码功能，包括但不限于： 1. **多速率自适应编码**：根据网络条件动态调整编码速率，保证在不同的网络环境下都能提供合适的音质。 2. **宽带编码**：提供比AMR-NB更宽的频率响应范围，有助于保留更多的语音细节，提升语音的自然性和保真度。 3. **透明的编码/解码过程**：确保在编码和解码过程中，音频质量的损失降到最低，即使在网络不稳定时也能保持流畅的通话体验。 4. **跨网络兼容性**：由于其在3G、4G以及后续技术如GSM（Global System for Mobile Communications）中的广泛支持，AMR-WB+能够在不同通信标准之间实现无缝转换。此外，该标准还规定了编码后的数据处理和转码功能，这对于支持多种设备和平台间的音频通信至关重要。在实际应用中，为了确保一致性，任何基于AMR-WB+的通信设备或服务必须遵守ETSITS 126290 V9.0.0的技术要求，比如下载文档的参考网址：http://www.etsi.org，以及指定的印刷版PDF作为官方参考。 AMR-WB+标准是现代移动通信技术中的关键组件，它通过优化音频编码技术，提升了语音通信的质量，为用户提供了一个更高效、更清晰的通话环境。随着网络技术的发展，AMR-WB+将继续在未来的通信系统中扮演重要角色。

ETSI

ETSI TS 126 290 V9.0.0 (2010

01)

3GPP TS 26.290 version 9.0

.0 Release 9

4.3.8 Bit allocation

The bit allocation for the different parameters in the low-frequency band coding (Core) (0-Fs/4 kHz band) is shown in

Tables 3, 4, 5, and 6. Note that there are two mode bits sent in each 256-sample packet. These mode bits are not shown

in the bit allocation tables. The bit allocations for the stereo part is shown in Tables 7, 8, and 9. Note that there are also

two additional mode bits for the VLF stereo encoder, which are not shown in the bit allocation. The bit allocation for

the stereo HF part is by definition that of the bandwidth extension, as presented in Tables 7,8 and 9.

Tables 2 and 3 show the total bits per 256-sample packet, including mode bits.

Table 3: Bit allocations for ACELP core rates including BWE (per frame)

Parameter

Number of bits

Mode bits 2

ISF Parameters 46

Mean Energy 2

Pitch Lag 30

Pitch Filter 4 × 1

Fixed-codebook

Indices

4 × 20 4 × 28 4 × 36 4 × 44 4 × 52 4 × 64 4 × 72 4 × 88

Codebook Gains 4 × 7

HF ISF Parameters 9

HF gain 7

Total in bits 208 240 272 304 336 384 416 480

Table 4: Bit allocations for 256-sample TCX window (Core)

Parameter

Number of bits

Mode bits 2

ISF Parameters 46

Noise factor 3

Global Gain 7

Algebraic VQ 134 166 198 230 262 310 342 406

HF ISF Parameters 9

HF gain 7

Total in bits 208 240 272 304 336 384 416 480

Table 5: Bit allocations for 512-sample TCX window (Core)

Parameter

Number of bits

Mode bits 2+2

ISF Parameters 46

Noise factor 3

Global Gain 7

Gain redundancy 6

Algebraic VQ 318 382 446 510 574 670 734 862

HF ISF Parameters 9

HF gain 7

HF Gain correction 8 × 2

Total in bits 416 480 544 608 672 768 832 960

ETSI

ETSI TS 126 290 V9.0.0 (2010

01)

3GPP TS 26.290 version 9.0.0 Release 9

5 Functional description of the encoder

In this clause, the different functions of the encoder extension modes represented in Figure 1 are described. Input

signals are understood as internal, i.e. sampled at the internal sampling frequency Fs.

5.1 Input signal pre-processing

Input signals are pre-processed in order to bring them to the internal sampling frequency of the encoder Fs kHz. The

signal is upsampled by a factor K (related to the desired internal sampling frequency), filtered by a a low pass filter and

then downsampled by a factor 180. This operation is efficiently implemented by a polyphase filter implementation.

Output signal Fs kHz

1/180



180



Input signal 180Fs /K kHz

The resulting signals are further decomposed into two equal critically sampled bands as shown in the following figure:

Input signal Fs kHz

2

)(nx

2048 samples

1024 samples

At an internal sampling rate of Fs kHz, the lower band signals are obtained by first low-pass filtering to Fs/4 kHz

critically downsampling the low-pass filtered signal to Fs/2 kHz. The higher band signals are obtained by band-pass

filtering the input signals to frequencies above Fs/4 kHz, and critically downsampling the high-pass filtered signal to

Fs/2kHz sampling frequency.

5.1.1 High Pass Filtering

The lower band signals are high pass filtered. The high-pass filter serves as a precaution against undesired low

frequency components. A high pass filter is used, and it is given by

aa1

bbb

)(

−−

+−

where the filter parameters are dependent on the internal sampling rate.

5.1.2 Stereo Signal Downmixing/Bandsplitting

When the input audio signal is stereo, the lower band mono signal is obtained by downmixing the left and right

channels according to the following

()

)()(5.0)( nxnxnx

RLLLML

where

)(nx

, resp. )(nx

, is the lower band signal from the left, resp. right, channels. The lower band mono signal

is supplied to the core low band encoder for TCX/ACELP encoding.

ETSI

ETSI TS 126 290 V9.0.0 (2010

01)

3GPP TS 26.290 version 9.0.0 Release 9

For stereo encoding, the obtained downmixed mono signal )(nx

and the right channel signal )(nx

are further

split into two bands: a critically sampled low frequency band and a residual high frequency band according to the

following diagram



5/32



32/5

delay

)(nx

MLo

)(nx

RLo

)(nx

MMid

)(nx

RMid

The critically sampled low band output signals, )(nx

MLo

and )(nx

RLo

are fed to the stereo low band encoder, while

the signals

)(nx

MMid

and )(nx

RMid

to the stereo mid band encoder.

5.2 Principle of the hybrid ACELP/TCX core encoding

The encoding algorithm at the core of the AMR-WB+ codec is based on a hybrid ACELP/TCX model. For every block

of input signal, the encoder decides (either in open-loop or closed-loop) which encoding model (ACELP or TCX) is

best. The ACELP model is a time-domain, predictive encoder, best suited for speech and transient signals. The AMR-

WB encoder is used in ACELP modes. Alternatively, the TCX model is a transform-based encoder, and is more

appropriate for typical music samples. Frame lengths of variable sizes are possible in TCX mode, as will be explained

in Section 5.2.1.

In Sections 5.2.1 to 5.2.4, the general principles of the hybrid ACELP/TCX core encoder will be presented. Then

Section 5.3 and its subsections will give the details of the ACELP and TCX encoding modes.

5.2.1 Timing chart of the ACELP and TCX modes

The ACELP/TCX core encoder takes a mono signal as input, at a sampling frequency of Fs/2 kHz. This signal is

processed in super-frames of 1024 samples in duration. Within each 1024-sample super-frame, several encoding modes

are possible, depending on the signal structure. These modes are: 256-sample ACELP, 256-sample TCX, 512-sample

TCX and 1024-sample TCX. These encoding modes will be described further, but first we look at the different possible

mode combinations, described by a timing chart.

Figure 4 shows the timing chart of all possible modes within an 1024-sample superframe. As the figure shows, each

256-sample frame within a super-frame can be into one of four possible modes, which we call ACELP, TCX256,

TCX512 and TCX1024. When in ACELP mode, the corresponding 256-sample frame is encoded with AMR-WB. In

TCX256 mode, the frame is encoded using TCX with a 256-sample support, plus 32 samples of look-ahead used for

overlap-and add since TCX is a transform coding approach. The TCX512 mode means that two consecutive 256-sample

frames are grouped to be encoded as a single 512-sample block, using TCX with a 512-sample support plus 64 samples

look-ahead. Note that the TCX512 mode is only allowed by grouping either the first two 256-sample frames of the

super-frame, or the last two 256-sample frames. Finally, the TCX1024 mode indicates that all 256-sample frames within

the super-frame are grouped together to be encoded in a single block using TCX with an 1024-sample support plus 128

samples look-ahead.

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AMR-WB+标准：3GPP协议推动移动网络音频编码新趋势

AMR-WB.zip

amr-wb 编码

AMR-WB+源码

3GPP语音及音频编码标准AMR-WB+定点C代码

3GPP AMR-WB+的参考代码

3GPP TS 26.290: AMR-WB+ Codec & Transcoding in UMTS and LTE

AMR-NB 与 AMR-WB 语音编码标准技术的对比研究

AMR-NB.zip_AMR-wb_DEMO_amr_amr nb_amr-nb code

AMR-WB源码

amrlib.rar_AMR-wb_amr_amr-nb_codec source library_interf_enc.h

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