Usually, speech coding and channel coding methods have to be chosen in pairs, with the more important bits in the speech data stream protected by more robust channel coding, in order to get the best overall coding results. The modified discrete cosine transform (MDCT), a type of discrete cosine transform (DCT) algorithm, was adapted into a speech coding algorithm called LD-MDCT, used for the AAC-LD format introduced in 1999.
MDCT has since been widely adopted in voice-over-IP (VoIP) applications, such as the G.729.1 wideband audio codec introduced in 2006, Apple's Facetime (using AAC-LD) introduced in 2010, and the CELT codec introduced in 2011. Opus is a free software speech coder.
Their audio performance remains acceptable, and there was no need to replace them in the stationary phone network. In 2008, G.711.1 codec, which has a scalable structure, was standardized by ITU-T.
MDCT has since been widely adopted in voice-over-IP (VoIP) applications, such as the G.729.1 wideband audio codec introduced in 2006, Apple's Facetime (using AAC-LD) introduced in 2010, and the CELT codec introduced in 2011. Opus is a free software speech coder.
MDCT has since been widely adopted in voice-over-IP (VoIP) applications, such as the G.729.1 wideband audio codec introduced in 2006, Apple's Facetime (using AAC-LD) introduced in 2010, and the CELT codec introduced in 2011. Opus is a free software speech coder.
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