aether-raid/astra-atc-models

ASTRA ATC Models

Fine-tuned models for Singapore military air traffic control, built for two training simulators:

• astra/ - ASTRA, the ATC training simulator (ASR and display formatter)
• par/ - the Precision Approach Radar (PAR) talkdown simulator (ASR)

The ASTRA and PAR models were developed separately for their own phraseology and callsigns, so they are not a single model: use the ASTRA ASR for ASTRA and the PAR ASR for PAR. Future work may train one ASR model that handles both.

astra/
  ASR/whisper/    Whisper Large v3 (legacy CTranslate2 backend)
  ASR/parakeet/   Parakeet-TDT 0.6B v2 (NeMo checkpoint)
  LLM/            Qwen3-1.7B display formatter (legacy)
par/
  ASR/            Parakeet-TDT 0.6B v2 (NeMo .nemo)

ASTRA

Pipeline

Audio  -->  VAD (Silero)  -->  ASR (Whisper or Parakeet)  -->  Rule Formatter  -->  Display Text
                               "camel climb flight level zero nine zero"
                                                                                  "CAMEL climb FL090"

The production pipeline uses a deterministic rule-based formatter instead of the legacy LLM formatter.

Models

astra/ASR/whisper/

Fine-tuned for Singapore military ATC speech. Uses CTranslate2 float16 format for fast inference with faster-whisper.

Metric	Value
WER	0.66%
Base model	openai/whisper-large-v3
Size	2.9 GB
Runtime	faster-whisper / CTranslate2

astra/ASR/parakeet/

Fine-tuned NeMo Parakeet model for Singapore military ATC speech. Published as a raw checkpoint together with the tokenizer artifacts required to restore it.

Metric	Value
Validation WER	0.72%
Base model	nvidia/parakeet-tdt-0.6b-v2
Size	7.0 GB
Runtime	nemo_toolkit[asr]

astra/LLM/

Legacy. Superseded by the deterministic rule formatter. Retained for reference only.

Converts normalized ASR output into structured ATC display text.

Metric	Value
Exact match	100% (161/161)
Base model	unsloth/Qwen3-1.7B
Size	3.3 GB

Architecture

Audio --> VAD (Silero) --> ASR backend --> Post-processing --> Rule Formatter --> Display Text

Component	Technology	Notes
VAD	Silero VAD	Shared frontend for both ASR backends
ASR (legacy)	Whisper Large v3 (CTranslate2)	Lower-memory legacy backend
ASR (current NeMo path)	Parakeet-TDT 0.6B v2	Fine-tuned NeMo checkpoint
Formatter	Deterministic rules	Converts normalized speech to ATC display text

Domain

Singapore military ATC covering Tengah and Paya Lebar operations, military phraseology, 100+ callsigns, and approach / recovery / emergency traffic.

Training History

ASR

Run	WER	Base	Key Change
ct2_run5	0.48%	jacktol/whisper-large-v3-finetuned-for-ATC	Initial fine-tune
ct2_run6	0.40%	jacktol/whisper-large-v3-finetuned-for-ATC	+augmentation, weight decay
ct2_run7	0.24%	jacktol/whisper-large-v3-finetuned-for-ATC	Frozen encoder, +50 real recordings
ct2_run8	0.66%	openai/whisper-large-v3	Full retrain from base, enhanced augmentation
parakeet_atc	0.72%	nvidia/parakeet-tdt-0.6b-v2	NeMo fine-tune with ATC radio augmentation, best checkpoint at epoch 76

LLM

Run	Accuracy	Key Change
llm_run3	98.1% (Qwen3-8B)	QLoRA 4-bit, 871 examples
llm_run4	100% (Qwen3-1.7B)	bf16 LoRA, 1,915 examples with ASR noise augmentation

Quick Start

Whisper ASR

from faster_whisper import WhisperModel

model = WhisperModel("./astra/ASR/whisper", device="cuda", compute_type="float16")
segments, info = model.transcribe("audio.wav", language="en", beam_size=5)
text = " ".join(seg.text.strip() for seg in segments)

Parakeet ASR

See astra/ASR/parakeet/README.md for the NeMo restore example and tokenizer artifact requirements.

PAR

par/ASR/

Fine-tuned for PAR talkdown speech: fast, clipped controller calls and pilot replies. Self-contained .nemo, so no tokenizer artifacts are needed. Details, results per test set and training stats in par/ASR/README.md.

Metric	Value
PAR held-out WER	0.17%
Base model	nvidia/parakeet-tdt-0.6b-v2
Size	2.5 GB
Runtime	nemo_toolkit[asr]

Download

# Full repo
huggingface-cli download aether-raid/astra-atc-models --local-dir ./models

# ASTRA Whisper ASR only
huggingface-cli download aether-raid/astra-atc-models --include "astra/ASR/whisper/*" --local-dir ./models

# ASTRA Parakeet ASR only
huggingface-cli download aether-raid/astra-atc-models --include "astra/ASR/parakeet/*" --local-dir ./models

# ASTRA LLM only (legacy)
huggingface-cli download aether-raid/astra-atc-models --include "astra/LLM/*" --local-dir ./models

# PAR ASR only
huggingface-cli download aether-raid/astra-atc-models --include "par/ASR/*" --local-dir ./models