Unified Speech and Audio Coding (USAC) is an audio compression

Audio compression

Audio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...

 format and codec

Audio codec

All codecs are devices or computer programs capable of coding or decoding a digital data stream or signal.The term audio codec has two meanings depending on the context:...

 for both music and speech or any mix of speech and audio using very low bit rates between 12 and 64 kbit/s. It is currently under the development in MPEG and will be defined as an international standard ISO

International Organization for Standardization

The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

/IEC

International Electrotechnical Commission

The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 23003-3 (a.k.a. MPEG-D

MPEG-D

MPEG-D is a group of standards for audio coding formally known as ISO/IEC 23003 - MPEG audio technologies, published since 2007.MPEG-D consists of three parts:* MPEG-D Part 1: MPEG Surround...

 Part 3) and also as an MPEG-4 Audio Object Type in ISO/IEC 14496-3:2009/Amd 3.

It uses time-domain linear prediction and residual coding tools (ACELP

ACELP

Algebraic code-excited linear prediction is a patented speech coding algorithm by VoiceAge Corporation in which a limited set of pulses is distributed as excitation to linear prediction filter....

-like techniques) for speech signal segments and transform coding tools (MDCT

Modified discrete cosine transform

The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...

-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

Spectral band replication

Spectral band replication is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain....

 (SBR) and MPEG-D MPEG Surround

MPEG Surround

MPEG Surround , also known as Spatial Audio Coding is a lossy compression format for surround sound that provides a method for extending mono or stereo audio services to multi-channel audio in a backwards compatible fashion...

parametric coding tools are integrated into the USAC codec.