Summary of pCR on Existing Codec Technologies (S4-260154)

Document Information

• Source: China Mobile Com. Corporation
• Specification: 3GPP TR 26.940 V0.5.1
• Meeting: TSG-SA WG4 Meeting #135, Goa, India, 09-13 February 2026

Purpose and Scope

This pCR proposes updates to Clause 7.1 of TR 26.940, which documents existing codec technologies for evidence that design criteria can be met and for comparison/evaluation purposes. The document adds information about recently emerged ultra-low bit-rate voice codecs (below 1 kbps) as reference for further work.

Main Technical Contributions

Expanded Codec Technology Reference Table

The pCR significantly expands Table 7.1.1-1 "List of existing codec technologies" by adding multiple categories of codecs beyond the existing 3GPP IMS codecs. The table includes the following parameters for each codec:

• Source/Reference
• Audio bandwidth (NB/WB/SWB/FB)
• Codec delay (ms)
• Frame duration (ms)
• Bitrates (kbps)
• Specification access/software availability

New Codec Categories Added

1. Conventional Ultra Low Bitrate Codecs

• MELP/MELPe: 0.6-2.4 kbps, NB, 22.5-90ms frame duration
• AMBE-LR: 1.6-1.8 kbps, NB
• MPEG-HVXC: 2-4 kbps, NB
• TWELP MR: 0.3-3.2 kbps, NB, various frame durations (40-120ms)
• Codec2: 0.45-2.4 kbps, NB, primarily 40ms frames

2. AI-Based Decoders

• WaveNet Codec2: 2.4 kbps, WB, 20ms frames
• CQNV Codec2: 1.0-1.1 kbps, WB, 40-60ms frames

3. AI-Based Encoder and Decoder (Causal)

These codecs support real-time operation:
- LPCNet: 1.6 kbps, WB, 40ms frames, 25ms delay
- LyraV2 (SoundStream): 3.2-9.2 kbps, WB, 20ms frames
- EnCodec: 1.5-24 kbps, 24kHz/FB, 0-1000ms delay, 13.3ms frames
- Mimi-Codec: 0.55-1.1 kbps, 24kHz, 80ms frames, 0ms delay
- TS3: 0.64-0.8 kbps, WB, 20ms frames, 0ms delay
- TAAE: 0.4-0.7 kbps, WB, 20-40ms frames, 0ms delay
- LMCodec2: Parameters TBD

4. AI-Based Encoder and Decoder (Non-Causal)

These codecs are designed for offline/non-real-time applications:
- DAC: 0.5-3 kbps, WB/24kHz, 244-366ms delay
- DAC-IBM: 0.75-3 kbps, 24kHz, 366ms delay
- SNAC: 0.98 kbps, 24kHz, 1000ms delay, 80ms frames
- SpeechTokenizer: 0.5-1.0 kbps, WB, full-signal delay
- SemantiCodec: 0.31-1.4 kbps, WB, 10-40ms frames, full-signal delay
- FunCodec: 0.25-1.0+ kbps, WB, 20-40ms frames
- WavTokenizer: 0.25-0.9 kbps, 24kHz, 25-40ms frames
- BigCodec: 1.04 kbps, WB, 12.5ms frames
- FocalCodec: 0.16-0.65 kbps, WB, 20-80ms frames
- ALMTokenizer: 0.41 kbps, WB, 13.3ms frames
- XY-Tokenizer: 1 kbps, WB, 20ms frames
- LongCat-Audio-Codec: 0.43-0.87 kbps, WB, 60ms frames
- AcademiCodec: Parameters TBD
- MuCodec: 0.35-1.35 kbps, FB

Additional Notes

The pCR includes several important notes:

• Note 1: Some codecs may include noise suppression
• Note 2: MPEG-HVXC decoder and reference encoder available only to MPEG members
• Note 3: Codec2 uses 20ms overlapping FFT/iFFT with overlap-add
• Note 4: Some codecs only have non-causal versions publicly available
• Note 5: TWELP has a complete quality assessment testbench available despite lacking open reference implementation

An editor's note indicates that more codecs may be added to the table in future revisions.

Key Observations

The pCR demonstrates significant industry progress in ultra-low bitrate speech coding, particularly:
- Multiple AI-based solutions achieving sub-1 kbps bitrates
- Wide range of delay characteristics (0ms to 1000ms)
- Various bandwidth support (NB to FB)
- Different availability levels for specifications and software implementations