| # Low Complexity Communication Codec (LC3) |
| |
| The LC3 is an efficient low latency audio codec. |
| |
| [_Low Complexity Communication Codec_](https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=502107&vId=542963) |
| |
| ## Overview |
| |
| The directory layout is as follows : |
| - include: Library interface |
| - src: Source files |
| - tools: Standalone encoder/decoder tools |
| - test: Python implentation, used as reference for unit testing |
| - build: Building outputs |
| - bin: Compilation output |
| |
| ## How to build |
| |
| The default toolchain used is GCC. Invoke `make` to build the library. |
| |
| ```sh |
| $ make -j |
| ``` |
| |
| Compiled library `liblc3.a` will be found in `bin` directory. |
| |
| #### Cross compilation |
| |
| The cc, as, ld and ar can be selected with respective Makefile variables `CC`, |
| `AS`, `LD` and `AR`. The `AS` and `LD` selections are optionnal, and fallback |
| to `CC` selection when not defined. |
| |
| The `LIBC` must be set to `bionic` for android cross-compilation. This switch |
| prevent link with `pthread` and `rt` libraries, that is included in the |
| bionic libc. |
| |
| Following example build for android, using NDK toolset. |
| |
| ```sh |
| $ make -j CC=path_to_android_ndk_prebuilt/toolchain-prefix-clang LIBC=bionic |
| ``` |
| |
| Compiled library will be found in `bin` directory. |
| |
| ## Tools |
| |
| Tools can be all compiled, while involking `make` as follows : |
| |
| ```sh |
| $ make tools |
| ``` |
| |
| The standalone encoder `elc3` take a `wave` file as input and encode it |
| according given parameter. The LC3 binary file format used is the non |
| standard format described by the reference encoder / decoder tools. |
| The standalone decoder `dlc3` do the inverse operation. |
| |
| Refer to `elc3 -h` or `dlc3 -h` for options. |
| |
| Note that `elc3` output bitstream to standard output when output file is |
| omitted. On the other side `dlc3` read from standard input when input output |
| file are omitted. |
| In such way you can easly test encoding / decoding loop with : |
| |
| ```sh |
| $ ./elc3 <in.wav> -b <bitrate> | ./dlc3 > <out.wav> |
| ``` |
| |
| Adding Linux `aplay` tools, you will be able to instant hear the result : |
| |
| ```sh |
| $ ./elc3 <in.wav> -b <bitrate> | ./dlc3 | aplay |
| ``` |
| |
| ## Test |
| |
| A python implementation of the encoder is provided in `test` diretory. |
| The C implementation is unitary validated against this implementation and |
| intermediate values given in Appendix C of the specification. |
| |
| #### Prerequisite |
| |
| ```sh |
| # apt install python3 python3-dev python3-pip |
| $ pip3 install scipy numpy |
| ``` |
| |
| #### Running test suite |
| |
| ```sh |
| $ make test |
| ``` |
| |
| ## Conformance |
| |
| The proposed encoder and decoder implementation have been fully tested and |
| validated. |
| |
| For more detail on conformance, refer to [_Bluetooth Conformance |
| Documents and scripts_](https://www.bluetooth.com/specifications/specs/low-complexity-communication-codec-1-0/) |
| |
| ## Listening Test |
| |
| The codec was [_here_](https://hydrogenaud.io/index.php/topic,122575.0.html) |
| subjectively evaluated in a blind listening test. |
| |
| ## Meson build system |
| |
| Meson build system is also available to build and install lc3 codec in Linux |
| environment. |
| |
| ```sh |
| $ meson build |
| $ cd build |
| $ ninja |
| $ sudo ninja install |
| ``` |
| |
