File size: 6,262 Bytes

---
license: apache-2.0
base_model: Audio8/ARK-ASR-3B
pipeline_tag: automatic-speech-recognition
language:
- en
- zh
- de
- ja
- fr
- ko
- es
- pl
- it
- ro
- hu
- cs
- nl
- fi
- hr
- sk
- sl
- et
- lt
tags:
- coreai
- aimodel
- aimodelc
- arkasr
- speech
- audio
- apple-silicon
---

# ARK-ASR-3B Core AI

Apple Core AI conversions of [Audio8/ARK-ASR-3B](https://huggingface.co/Audio8/ARK-ASR-3B), made from source revision `1e28271b79edc97635783bea65abc89195a09ed3`.

ARK-ASR combines a Whisper-style audio encoder, an MLP adapter, and a Qwen2.5 decoder. These files use Apple's Core AI runtime (macOS 27+); they are **not** GGUF and are **not** compatible with `llama.cpp`, `whisper.cpp`, or Apple's `CoreAISpeech` bundle layout. For GGUF runtimes see [harshav/ARK-ASR-3B-GGUF](https://huggingface.co/harshav/ARK-ASR-3B-GGUF).

## Artifact forms

| Term | Meaning |
| --- | --- |
| `.aimodel` | Portable Core AI source asset. Runs on any macOS 27+ device; the runtime specializes it for your chip on first use (one-time, cached). |
| `.aimodelc` | AOT-compiled variant for one specific silicon architecture, produced by `xcrun coreai-build compile --architecture <arch>`. Skips runtime specialization entirely (measured 74 s → ~0 s of model preparation per app launch). The runtime **hard-rejects** mismatched chips with `incompatibleCompiledAssetArchitecture`, so only use the variant matching your device (`h16c` = M4 Max family; list yours with `xcrun coreai-build list-architectures`). Other architectures compile from the `.aimodel` in minutes. |
| `fp16` | Full-precision weights (encoder). |
| `int8` | Weight-only quantization, per-block-32 symmetric with clipping (decoder). SDPA, RoPE, RMSNorm, embeddings, and the LM head stay in fp16. |
| `static` | The prefill graph's prompt shape is baked (2 + 375 audio slots + 3 = 380 tokens, the constant 30 s window). A dynamic-shape prefill costs ~3 GB more compiled package and ~4x slower gate load for zero behavior change. |

The decoder is one unified bundle: `prefill` + `decode` entrypoints share a single weight copy, with the KV cache externalized and threaded host-side.

## Runtime

`coreai-arkasr-conversion.tar.gz` is the complete conversion and verification toolkit used to produce and gate these artifacts (SHA-256: `8a24d7069ec64462703986445af5841541e626235cf03c53ece8d3aefc08d77f`), including the port's `STATE.md` with full reproduction steps:

```bash
tar -xzf coreai-arkasr-conversion.tar.gz && cd ark_asr
uv run --python 3.12 make_oracle.py --audio <16k.wav>
uv run --python 3.12 --with-editable <coreai-models>/python export_encoder.py --dtype float16
uv run --python 3.12 --with-editable <coreai-models>/python export_unified.py --mode int8 --cache-len 1024 --static-prefill
uv run --python 3.12 gate_static.py --unified --mode int8 --cache-len 1024
```

The reference client is [VoiceInk](https://github.com/Beingpax/VoiceInk) (`Transcription/CoreAI/`): mel frontend, prompt splicing (`vocabSize + slot` audio injection), host KV cache, greedy decode. `runtime_config.json`, `mel_filters.f32`, and the tokenizer files are the exact inputs that client consumes. Audio input is 16 kHz mono.

## Files

```text
encoder.aimodel/                 fp16 Whisper tower + MLP adapter
encoder.h16c.aimodelc/           AOT-compiled encoder (h16c / M4 Max only)
decoder.aimodel/                 int8 static unified prefill+decode
decoder.h16c.aimodelc/           AOT-compiled decoder (h16c / M4 Max only)
runtime_config.json              prompt/config constants for clients
mel_filters.f32                  exact slaney mel filterbank from ARK's feature extractor
tokenizer*.json, vocab.json, merges.txt, added_tokens.json, special_tokens_map.json
coreai-arkasr-conversion.tar.gz  conversion + gate toolkit
```

| Payload | Size | SHA-256 |
| --- | ---: | --- |
| `encoder.aimodel/main.mlirb` | 1,329,458,070 bytes | `14bfbb6d1503c6cf26686a3aa855614cd33a1d0cc686698788697f542fb0055c` |
| `decoder.aimodel/main.mlirb` | 3,572,562,869 bytes | `e324f285d79421f18baea5213a3b021b813df7d15e009f01260b64517bd90b4d` |
| `encoder.h16c.aimodelc` resources.bin | 1,328,929,212 bytes | `7ba10b5317d5fb1eee88df8ec3a318ac43984cfa25221bbd8f2f8dbde7172f1b` |
| `decoder.h16c.aimodelc` resources.bin | 12,966,484,252 bytes | `88385079c215b51ad522b62c436a3a1ab72987f10d2d99128e0cb54d53ad871e` |

Do not recompute the mel filterbank: Whisper uses slaney-scaled normalized triangles (peak ≈ 0.042), and the textbook HTK formula diverges by ~24x, which measurably corrupts transcription. Use `mel_filters.f32` as shipped.

## Local validation

Gated on an Apple M4 Max (h16c), macOS 27.0 (26A5388g), `coreai-core` 1.0.0b2, `coreai-torch` 0.4.1, against an fp32 PyTorch golden of the official model. The pass condition is exact token-for-token equality, not similarity.

| Stage | Result |
| --- | --- |
| encoder `.aimodel` vs fp32 golden, real-audio rows | cosine mean 0.999998, min 0.999901 |
| full pipeline greedy decode | **42/42 tokens identical** to PyTorch |

Performance on the same machine (12.75 s clip):

| Metric | fp16 dynamic | int8 static (this repo) |
| --- | ---: | ---: |
| gate load | 62.7 s | **3.4 s** |
| prefill | 1.75 s | **0.31 s** |
| decode | 71.0 ms/tok | **51.8 ms/tok** |
| app prewarm, fresh process | 127 s | **74 s** |

Architecture note: ARK decodes autoregressively through a 36-layer 3B LLM, so ~52 ms/token is a bandwidth floor every framework hits, GGUF/llama.cpp included. Purpose-built ASR models (e.g. Cohere Transcribe) are structurally faster for short dictation.

## Long audio

The model is a fixed 30-second-window architecture: the official feature extractor pads or trims mel to 3000 frames, and a 33.5 s probe confirms the reference implementation truncates at the window edge. Longer audio is a host-side concern — window the input (the GGUF runtime in [harshav/ARK-ASR-3B-GGUF](https://huggingface.co/harshav/ARK-ASR-3B-GGUF) overlaps windows by 2 s and stitches) and concatenate transcripts.

## License and attribution

The original model is Apache-2.0 licensed. See the [official model card](https://huggingface.co/Audio8/ARK-ASR-3B) and [AutoArk repository](https://github.com/AutoArk/open-audio-opd) for architecture, training, and upstream attribution.