This Recommendation provides source code for speech and audio processing modules for narrowband, wideband and super-wideband telephony applications. The set includes codecs, filters, noise generators, etc. This revision introduces changes to ITU-T G.191 Annex A, which describes the ITU-T Software Tools (STL) containing a high-quality, portable C code library for speech processing applications. This new release of the STL, also known as STL2018, incorporates new basic operators to accommodate state-of-the-art processor architectures which supports wide accumulators, SIMD (Single Instruction Multiple Data) and VLIW (Very Long Instruction Word). Thus the new operators provides support for 64-bit accumulator, complex numbers, enhanced 32-bit operations and additional control code operators. The software package was reworked to make it available as a truly open-source project and is therefore hosted on an open-source collaboration platform. The build toolchain is now using CMake to generate platform-dependent and tool-dependent build scripts as well as to execute regression tests for each module in the STL. This Recommendation includes an electronic attachment containing STL2018 Software Tool Library and manual.

For the purpose of the AAP Last Call, the electronic attachment is available at https://www.itu.int/ifa/t/2017/sg12/exchange/plenary/q2/g191_2018/G.191-Attachment.zip