增强型全速率（Enhanced Full Rate） 或 EFR 或 GSM-EFR 或 GSM 06.60 是一种 速度编码（speech coding）的标准。它的开发目的是改善质量相当糟糕的 GSM 全速率（FR）编解码器。工作速率 12.2 kbit/s 的 EFR 提供线材级的低噪质量。 EFR 12.2 kbit/s 速度编码标准同最高的 AMR 模式 相兼容（两者都属于 ACELP）。尽管这样，增强型全速率着眼点是改善呼叫质量，它的编解码有较高的计算复杂性，它会导致移动设备相比以前的 FR 编解码功耗增加 5%。 EFR 是 Nokia 和 University of Sherbrooke (Canada) 合作开发的。ETSI 于 1995 年将其作为 GSM/DCS 的工业标准。 TechnologyThe sampling rate is 8000 sample/s leading to a bit rate for the encoded bit stream of 12.2 kbit/s. The coding scheme is the so-called Algebraic Code Excited Linear Prediction Coder (ACELP). The encoder is fed with data consisting of samples with a resolution of 13 bits left justified in a 16-bit word. The three least significant bits are set to 0. The decoder outputs data in the same format.[2] The Enhanced Full Rate (GSM 06.60) technical specification describes the detailed mapping between input blocks of 160 speech samples in 13-bit uniform PCM format to encoded blocks of 244 bits and from encoded blocks of 244 bits to output blocks of 160 reconstructed speech samples. It also specifies the conversion between A-law or μ-law (PCS 1900) 8-bit PCM and 13-bit uniform PCM. This part of specification also describes the codec down to the bit level, thus enabling the verification of compliance to the part to a high degree of confidence by use of a set of digital test sequences. These test sequences are described in GSM 06.54 and are available on disks.[2] This standard is defined in ETSI ETS 300 726 (GSM 06.60). The packing is specified in ETSI Technical Specification TS 101 318.[3] ETSI has selected the Enhanced Full Rate voice codec as the industry standard codec for GSM/DCS in 1995. Enhanced Full Rate was also chosen as the industry standard in US market for PCS 1900 GSM frequency band.[1][4] Licensing and patent issuesThe Enhanced Full Rate incorporate several patents. It uses the patented ACELP technology, which is licensed by the VoiceAge Corporation.[5][6][7][8] Enhanced Full Rate was developed by Nokia and the University of Sherbrooke (Canada).[1] to enable and disable (Nokia 3310)To enable EFR type *3370#.. it will be automatically enabled. To disable EFR type #3370#.. from: http://en.wikipedia.org/wiki/Enhanced_Full_Rate |
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