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26 series - Voice and audio codecs

26.943 - Recognition performance evaluations of codecs for Speech Enabled Services (SES) 26.177 - Speech Enabled Services (SES); Distributed Speech Recognition (DSR) extended advanced front-end test sequences 26.243 - ANSI C code for the fixed-point distributed speech recognition extended advanced front-end 26.231 - Cellular text telephone modem; Minimum performance requirements 26.230 - Cellular text telephone modem; Transmitter bit exact C-code 26.226 - Cellular text telephone modem; General description 26.103 - Speech codec list for GSM and UMTS 26.132 - Speech and video telephony terminal acoustic test specification 26.131 - Terminal acoustic characteristics for telephony; Requirements 26.115 - Echo control for speech and multimedia services Enhanced aacPlus codec AMR-WB codec AMR codec Up to the 26 series


The voice & audio specifications that are listed here cover the following issues:

  • Echo control at the interface to the public switched telephone network.
  • The acoustic characteristics of 3G phones.
  • The codecs supported during transcoder-free operation, in which the compressed speech frames travel all the way from one mobile to the other, without any transcoders in the communication path.
  • Text telephones for the hard-of-hearing.
  • Distributed speech recognition, in which the speech is parameterised before transmission, so as to avoid degradation of the signal over the radio interface.

The codecs themselves (AMR, AMR-WB and enhanced aacPlus) are covered on the pages indicated at the top.


AACAdvanced audio coding
AMRAdaptive multi-rate
AMR-WBAdaptive multi-rate wide-band
ETSIEuropean telecommunications standards institute
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