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BRACE: A Benchmark for Robust Audio Caption Quality Evaluation
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Introduces BRACE, a reference-free benchmark with BRACE-Main (human/machine caption pair comparison) and BRACE-Hallucination (LLM noun-substitution hallucinations) to evaluate CLAPScore-style audio caption metrics and large audio language models.
Problem
Reference-free evaluation of audio captions (e.g., CLAPScore) lacks systematic validation of robustness, and existing benchmarks do not test full-caption quality comparison or full-length caption hallucination detection in audio.
Approach
Build pairwise audio-caption comparison data from AudioCaps/Clotho evaluation sets (LALM-generated and LLM-corrupted captions, with three-annotator consensus filtering) plus LLM-generated noun-substitution hallucinations, and use it to meta-evaluate CLAP-based metrics and LALMs; also proposes a sliding-window CLAP embedding to reduce run-to-run variance.
Key results
- Best CLAP-based metric (SLIDE-CLAP LAION-CLAP) reaches 70.01 average F1 on BRACE-Main; best LALM AF2 reaches 63.19.
- On BRACE-Hallucination, GPT-4o-Audio-Preview attains 96.37 F1 while the best open-source LALM Qwen-Audio-Chat reaches 77.25.
- CLAP models reach no more than 70 on HH and MM pairs in BRACE-Main, indicating weak fine-grained caption discrimination.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Apply sliding-window audio embedding aggregation instead of standard CLAP audio-window handling (ablation) | CLAP models on BRACE-Main · BRACE-Main | F1-score: 68.93 -> 70.01 | Helped |
| Add reference captions to CLAP evaluation (ablation) | CLAP models · BRACE-Main Avg | F1-score: 71.54 -> 72.74 | Helped |
| Add reference captions to CLAP evaluation (ablation) | CLAP models · BRACE-Hallucination Avg | F1-score: 95.85 -> 97.92 | Helped |
| Use simple rather than naive prompt wording (ablation) | Qwen-Audio-Chat · BRACE-Main | F1-score: 28.99 -> 59.64; 17.69 -> 59.84 | Mixed |
| Use complex rather than naive prompt wording (ablation) | AF2 · BRACE-Main | F1-score: 62.94 -> 1.35; 63.19 -> 3.26 | Hurt |
| Provide a tie option in a naive prompt (ablation) | GPT-4o-Audio-Preview · BRACE-Main | F1-score: 68.30 -> 69.50 | Helped |
| Provide a tie option in a naive prompt (ablation) | AF2 · BRACE-Main | F1-score: 62.94 -> 63.19 | Helped |
| Add a single reference caption and use a simple tie prompt (ablation) | Qwen2-Audio-Instruct · BRACE-Main | F1-score: 52.73 -> 64.24 | Helped |
| Add a single reference caption and use a simple non-tie prompt (ablation) | Qwen2-Audio-Instruct · BRACE-Hallucination | F1-score: 59.46 -> 79.00 | Helped |
| Filter low-agreement caption pairs (ablation) | BRACE benchmark annotations · AudioCaps and Clotho | Fleiss' Kappa: 0.3806 -> 0.9822; 0.4380 -> 0.8422 | Helped |
| Add reference captions to most LALM prompts (ablation) | LALMs · BRACE benchmarks | F1-score | Mixed |
Surprising findings
- Several LALMs (e.g., GAMA) score near or below chance on BRACE-Main, with strong position bias toward caption_0 or caption_1.
- Adding reference captions helps CLAP models but tends to hurt most LALMs.
Limitations
- Benchmark is restricted to existing open-source datasets (AudioCaps, Clotho), limiting diversity across languages, cultures and acoustic environments.
- LALM evaluation is expensive (up to 14 hours per round), so LALM results come from single runs without error bars.
- LALM outputs are distilled to preferences using a secondary LLM, adding a possible source of error.
Experimental setup
Datasets: AudioCaps Clotho
Benchmarks: BRACE-Main BRACE-Hallucination
Metrics: F1-score accuracy by caption pair type
Baselines: MS-CLAP-2022 MS-CLAP-2023 M2D-CLAP LAION-CLAP LTU GAMA Qwen-Audio-Chat Qwen2-Audio-Instruct AF2 GPT-4o-Audio-Preview
Builds on: CLAPScore CLAP FENSE Comp-A AudioCaps Clotho
Closest papers by meaning
- ADIFF: Explaining audio difference using natural language (ICLR 2025 · similarity 0.86)
- Unbiased Sliced Wasserstein Kernels for High-Quality Audio Captioning (NeurIPS 2025 · similarity 0.86)
- An eye for an ear: zero-shot audio description leveraging an image captioner with audio-visual token distribution matching (NeurIPS 2024 · similarity 0.84)
- TTA-Bench: A Comprehensive Benchmark for Evaluating Text-to-Audio Models (AAAI 2026 · similarity 0.84)
- OmniCapBench: A Deep-Structured Evaluation Framework for Fine-Grained Audio-Visual Captioning (NeurIPS 2026 · similarity 0.84)
- Synthio: Augmenting Small-Scale Audio Classification Datasets with Synthetic Data (ICLR 2025 · similarity 0.84)
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