第三代移动通信工作组3GPP2为了满足宽带语音编码的需要, 着手开发一种用于CDMA2000系统的宽带编码标准。经过对几个候选声码器的严格评估之后, 3GPP2于2003年选择了由诺基亚设计的变速率多模式的带宽（VMR-WB）编码器作为标准。VMR-WB是一种新型可变速率多模式宽带语音声码器, 用于 50Hz 一 7000Hz频带上进行语音编码, 采样频率为16KHz。VMR-WB根据每一帧信号的特点和选择的运行模式, 通过内置的速率选择机制来选择一个对应的编码类型,可选择的速率分别为13.3kpbs的全速率(FR)、6.2kpbs的半速率(HF)、2.7kbps的四分之一速率(QR)、1.0kpbs的八分之一速率(ER)。VMR-WB语音声码器是基于自适应多速率宽带AMR-WB语音声码器的核心算法上实现的, 因此可以和AMR-WB的其中一种运行模式兼容。
通过wiki可以下载到VMR-WB spec and bit-stream payload
Variable-Rate Multimode Wideband (VMR-WB) is a source-controlled variable-rate multimode codec designed for robust encoding/decoding of wideband/narrowband speech. The operation of VMR-WB is controlled by speech signal characteristics (i.e., source-controlled) and by traffic condition of the network (i.e., network-controlled mode switching). Depending on the traffic conditions and the desired quality of service (QoS), one of the 4 operational modes is used. All operating modes of the existing VMR-WB standard are fully compliant with cdma2000 rate-set II. VMR-WB modes 0, 1, and 2 are cdma2000 native modes with mode 0 providing the highest quality and mode 2 the lowest ADR. VMR-WB mode 3 is the AMR-WB interoperable mode operating at an ADR slightly higher than mode 0 and providing a quality equal or better than that of AMR-WB at 12.65 kbit/s when in an interoperable interconnection with AMR-WB at 12.65 kbit/s.
Now also a cdma2000 rate-set I compliant mode is implemented to the coder as mode 4. The average bitrate of the mode is 6.1 kbit/s (maximum is 8.55 kbit/s).
VMR-WB can be also used in 3GPP2 container file format - 3G2.
linking:http://en.wikipedia.org/wiki/Variable-Rate_Multimode_Wideband
spec: http://www.3gpp2.org/public_html/specs/C.S0052-0_v1.0_040617.pdf
总结一下：VMR—WB其实就是结合了EVRC 和AMR-WB 技术，是一种组合技术，但同时也考虑了与现有的Codec 兼容性问题。这也是技术创新的一种方法，很多标准和专利都是基于已有的技术改进而来的。
VMR-WB向EVRC 或QCELP 引进了速率判决功能，根据源来选择不同的速率来对语音进行编码。