自适应多速率音频压缩

自适应多速率(AMR)
扩展名
.amr
互联网媒体类型
audio/amr, audio/3gpp, audio/3gpp2
格式类型音频

自适应多速率音频压缩Adaptive multi-Rate compression,简称AMR)是一个使语音编码最优化的专利。AMR被标准语音编码 3GPP在1998年10月选用,现在广泛在GSMUMTS中使用。它使用1-8个不同的位元率編碼。

AMR 也是一个文件格式,存储AMR 语音编码文件. 很多手机允许使用者存储短时间的AMR 格式录音,而部分开源(参看外部链接)和商业软件有和其他格式转换的程序。但是AMR是一个语音格式,並未針對其他聲音進行最佳化。普通文件扩展名.amr

使用

为保证每20毫秒160采样点的采样率,AMR使用ACELP、DTX、VAD和CNG等不同的技术,从中选择最好的编码模式适应局部信道和通路频带要求。如果广播条件差,源编码减少,信道编码增加。此舉可提高网络连接的品質,但必須牺牲语音的清晰度。在特别情况下AMR 增加大约S/N = 4-6 dB。

以下列出共计14种方式的AMR编码,包含8个全频(FR)和6个半频(HR)。

Mode Bitrate (kbit/s) Channel 兼容
AMR_12.20 12.20 FR ETSI GSM enhanced full rate
AMR_10.20 10.20 FR
AMR_7.95 7.95 FR/HR
AMR_7.40 7.40 FR/HR TIA/EIA IS-641 TDMA enhanced full rate
AMR_6.70 6.70 FR/HR ARIB 6.7 kbit/s enhanced full rate
AMR_5.90 5.90 FR/HR
AMR_5.15 5.15 FR/HR
AMR_4.75 4.75 FR/HR
AMR_SID 1.80 FR/HR

特点

  • 采样率 8 kHz/13-bit (160 采样点每20ms),滤波后只保留 200-3400 Hz 范围内的信号。
  • 编码器使用8个位速:12.2、10.2、7.95、7.40、6.70、5.90、5.15和4.75 kbit/s。
  • 生成的帧长度为95、103、118、134、148、159、204或244bit,对应的位速分别为4.75、5.15、5.90、6.70、7.40、7.95、10.2或12.2 kbit/s。
  • AMR利用 Discontinuous Transmission (DTX), Voice Activity Detection (VAD)和Comfort Noise Generation (CNG)减少在无声时候的带宽。
  • 算法延迟是每帧20ms。位速是12.2的时候,没有前瞻延迟。其他速率的前瞻延迟是5 ms. 注有5 ms 的仿前瞻延迟,允许准确的帧宽模式转换其余速率。
  • AMR是使用 Algebraic Code Excited Linear Prediction (ACELP)的混合语言编码器。
  • 运算法则的复杂性是5的话,则 G.711 是1 G.729a 是15。
  • PSQM在理想条件下测试失真Mean Opinion Scores AMR(12.2 kbit/s)是 4.14,相比G.711 (u-law) 是 4.45。
  • PSQM在网络条件下Mean Opinion Scores AMR(12.2 kbit/s)是3.79,相比G.711 (u-law) 是4.13。

专利许可

AMR编解码器数个专利:

參見

外部链接

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