Recommendation ITU-T G.191 provides source code for speech and audio processing modules for narrowband, wideband and super-wideband telephony applications. The set includes codecs, filters and noise generators.

This edition introduces changes to , which describes the ITU-T software tool library (STL) containing a high-quality, portable C code library for speech-processing applications. This release of the STL, also known as STL2019, incorporates new basic operators to accommodate state-of-the-art processor architectures that support wide accumulators, single instruction multiple data (SIMD) and very long instruction word (VLIW). Thus, the new operators provide 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 now uses CMake to generate platform-dependent and tool-dependent build scripts, as well as to execute regression tests for each module in the STL.

Recommendation ITU-T G.191 includes an electronic attachment containing STL2019 and manual.