Unified Speech and Audio Coding

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Unified Speech and Audio Coding (USAC) is an audio compression format and codec for both music and speech or any mix of speech and audio using very low bit rates between 12 and 64 kbit/s.[1] It was developed by Moving Picture Experts Group (MPEG) and was published as an international standard ISO/IEC 23003-3 (a.k.a. MPEG-D Part 3)[2] and also as an MPEG-4 Audio Object Type in ISO/IEC 14496-3:2009/Amd 3 in 2012.[3]

It uses time-domain linear prediction and residual coding tools (ACELP-like techniques) for speech signal segments and transform coding tools (MDCT-based techniques) for music signal segments and it is able to switch between the tool sets dynamically in a signal-responsive manner. It is being developed with the aim of a single, unified coder with performance that equals or surpasses that of dedicated speech coders and dedicated music coders over a broad range of bitrates. Enhanced variations of the MPEG-4 Spectral Band Replication (SBR) and MPEG-D MPEG Surround parametric coding tools are integrated into the USAC codec.[4][5]

See also[edit]

Opus (codec) – a royalty free alternative, low latency codec for a similar usage


  1. ^ Fraunhofer Institute for Integrated Circuits. "Unified Speech and Audio Coding". Retrieved 2011-07-18. 
  2. ^ "ISO/IEC DIS 23003-3 - Information technology -- MPEG audio technologies -- Part 3: Unified speech and audio coding". 2011-02-15. Retrieved 2011-07-18. 
  3. ^ "ISO/IEC 14496-3:2009/PDAM 3 - Transport of unified speech and audio coding (USAC)". 2011-06-30. Retrieved 2011-07-18. 
  4. ^ MPEG. "Work Plan and Time Line". Retrieved 2011-07-18. 
  5. ^ "Unified Speech and Audio Coder Common Encoder Reference Software". March 2011. Retrieved 2011-07-18.