Low Complexity Communication Codec (LC3)

Low Complexity Communication Codec (LC3) is the default software codec for the nRF5340 Audio application, conformant to the Bluetooth® LE Audio specifications (Bluetooth 5.2, QDID #156294). For more information about the codec usage in the application, see the application documentation page in the nRF Connect SDK documentation.

The nrfxlib module includes the lc3/include/sw_codec_lc3.h and lc3/src/sw_codec_lc3.c files that form a translation layer for using a standardized API in the nRF5340 Audio application.

License and attribution

For the terms and conditions for using the LC3 codec, see license.txt and attribution.txt at lc3/.

API documentation

For API documenation, check the LC3 API documentation file.


All notable changes to this project are documented in this section.

nRF Connect SDK v2.1.0

Initial release in the sdk-nrxlib repository. This release includes the following changes to the codec.

LC3 v1.0.4

Build information:

  • Platform: ARM Cortex-M33, Cortex-M44

  • Compiler: ARM v6, -Ofast

  • Hard floating point, fixed point


  • Replaced floating point stdlib dependencies in data path with T2 functions.

  • Optimized the LTPF decoder, fixed point.

LC3 v1.0.3


  • MDCT optimizations.

  • LTPF optimizations.

  • Arithmetic encoding optimizations.

LC3 v1.0.2


  • Platform-specific optimizations.

LC3 v1.0.1


  • Fixed point optimizations.

LC3 v1.0.0


  • ARC LTPF SIMD optimizations.

LC3 v0.9.14


  • ARM optimizations.

LC3 v0.9.13


  • Added compile option to separate encode/decode memory.

LC3 v0.9.12


  • ARM optimizations.

LC3 v0.9.11


  • ARM optimizations.

LC3 v0.9.10


  • Incorporated all technical errata up to 15138.

LC3 v0.9.9


  • Non-functional changes.

LC3 v0.9.8


  • Fixed point memory optimizations.

  • Fixed point 7.5 ms frame size conformance improvements, meets stricter 0.06 ODG threshold in conformance tests.

  • Fixed scaling for > 16 bit PCM output in fixed point.

LC3 v0.9.7


  • Fixed Glockenspiel 24 kHz / 48 kbps / 7.5 ms exceeding 0.06 ODG in floating point encode/decode test.

  • Performance optimizations.

LC3 v0.9.6


  • Added 7.5 ms support for floating point.

LC3 v0.9.5


  • Fixed point memory optimizations.

LC3 v0.9.4


  • Added 24 and 32 bit PCM input and output to T2_LC3.

  • Optimizations in pitch lag detection.

  • Added API for amount of packet loss correction (PLC) applied.

  • Added API for providing static buffers.

  • Added error code offset to avoid value conflict with other modules.

  • Added API for the number of bytes read from encoder input.

LC3 v0.9.3


  • Fixed an issue in T2_LC3 where decoding a single frame resulted in 1/4 frame of additional PCM output.

LC3 v0.9.2


  • Added x64 Linux build T2_LC3.

  • Added support for multi-channel WAV files to T2_LC3 application.

  • Removed a DLL dependency from T2_LC3 Windows build.