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, noise generators. This edition introduces changes to Annex A, which describes the ITU-T Software Tools (STL) containing a high-quality, portable C code library for speech processing applications. This release of the STL, also known as STL2026, incorporates: WAV file I/O support with multi-bit-depth (16/24/32-bit) processing for all tools Extensions to the speech voltmeter (sv56) for arbitrary bit-depth processing A delay-and-error profile to frame-erasure pattern conversion tool (dlyerr_2_errpat) for jitter buffer emulation (3GPP S4-121077) An EID for 3GPP AMR bitstreams (eid-amr) A pseudo-random selection tool (random) for EVS processing scripts (3GPP S4-121078) SHQ2/SHQ3 half-band and HP50 high-pass FIR filters P.863/P.863.2 resampling FIR filters for rate-change factors 2, 3, 4 and 6 (as published in ETSI TR 103 138) A per-band gain verification tool (gain_chk) for codec and speech-processing validation Cross-platform portability fixes with expanded CTest regression coverage Recommendation ITU-T G.191 includes an electronic attachment containing STL2026 and manual.

TSB Note: For the purpose of the AAP Last Call, the electronic attachment (181 MB) is available at https://www.itu.int/ifa/t/2025/sg12/exchange/plenary/q02/G.191-attachment.zip