APTX apt-X Lossless White Paper

apt-X Lossless is an audio codec developed by APTX (APT Licensing Ltd.) for the lossless compression of digital audio (including music, natural and synthetic speech, etc) This paper explains an entirely new scheme for lossless audio compression - apt-X Lossless.

apt-X Lossless supports high-definition audio up to 96 kHz sampling rates and sample resolutions up to 24 bits. The codec optionally permits a “hybrid” coding scheme for applications where average and/or peak compressed data rates must be capped at a constrained level. This involves the dynamic application of a mild form of lossy coding only for the short sections of audio where completely lossless coding cannot respect the bandwidth constraints. Even for the short periods whilst the lossy coding is active, the audio quality is maintained at a high level, retaining audio frequencies up to 20 kHz and a dynamic range of at least 120 dB for high-definition audio.

Due to their simpler signal processing functions, many lossless codecs possess a low computational complexity compared to well-known lossy codecs such as MP3 and AAC. This is particularly important for deeply-embedded audio applications running on low-power mobile devices. apt-X Lossless promotes low computational complexity in a novel way by supporting dynamic adaptation of the signal processing functions used to code each short segment of audio in such a way that the computational complexity of the selected functions is minimized whilst respecting other configured constraints, such as levels of compression and coding delay. Depending on the settings of other scalable parameters, apt-X Lossless can encode a 48 kHz 16-bit stereo audio stream using only 10 MIPS on a modern RISC processor with signal processing extensions. The corresponding decoder represents only 6 MIPS on the same platform.

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