5 Adaptive Multi-Rate Wideband speech codec transcoding functions

26.1713GPPAdaptive Multi-Rate - Wideband (AMR-WB) speech codecGeneral descriptionSpeech codec speech processing functionsTS

The adaptive multi-rate wideband speech codec is described in [2].

As shown in Figure 1, the speech encoder takes its input as a 14-bit uniform Pulse Code Modulated (PCM) signal either from the audio part of the UE or from the network side [TBD] or from the Public Switched Telephone Network (PSTN) via an narrowband 13-bit A-law or -law to wideband 14-bit uniform PCM conversion. An upsampling by factor of 2 has to be performed between narrowband and wideband speech signals. The encoded speech at the output of the speech encoder is packetized and delivered to the network interface. In the receive direction, the inverse operations take place.

The detailed mapping between input blocks of 320 speech samples in 14-bit uniform PCM format to encoded blocks (in which the number of bits depends on the presently used codec mode) and from these to output blocks of 320 reconstructed speech samples is described in [2]. The coding scheme is Multi-Rate Algebraic Code Excited Linear Prediction. The bit-rates of the source codec are listed in Table 1.

An AMR-WB speech codec capable UE shall support all source rates listed in Table 1.

Table 1: Source codec bit-rates for the AMR-WB codec

Codec mode	Source codec bit-rate
AMR-WB_23.85	23.85 kbit/s
AMR-WB_23.05	23.05 kbit/s
AMR-WB_19.85	19.85 kbit/s
AMR-WB_18.25	18.25 kbit/s
AMR-WB_15.85	15.85 kbit/s
AMR-WB_14.25	14.25 kbit/s
AMR-WB_12.65	12.65 kbit/s
AMR-WB_8.85	8.85 kbit/s
AMR-WB_6.60	6.60 kbit/s
AMR-WB_SID	1.75 kbit/s *

(*) Assuming SID frames are continuously transmitted