# 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