Swiss Parliaments Corpus Re-Imagined (SPC_R): Enhanced Transcription with RAG-based Correction and Predicted BLEU

TL;DR

This paper introduces an enhanced Swiss Parliaments Corpus with high-quality transcriptions achieved through a multi-step correction process using GPT-4o and BLEU-based filtering, resulting in a large, accurate speech-text dataset.

Contribution

It presents a novel pipeline combining Whisper ASR, GPT-4o correction, and BLEU-based filtering to produce a high-quality, long-form Swiss German speech corpus.

Findings

Achieved a 6-point BLEU score improvement over previous corpus versions.

Filtered 555 hours of high-quality transcriptions from 801 hours of audio.

Demonstrated the effectiveness of LLM-based correction and filtering for low-resource domains.

Abstract

This paper presents a new long-form release of the Swiss Parliaments Corpus, converting entire multi-hour Swiss German debate sessions (each aligned with the official session protocols) into high-quality speech-text pairs. Our pipeline starts by transcribing all session audio into Standard German using Whisper Large-v3 under high-compute settings. We then apply a two-step GPT-4o correction process: first, GPT-4o ingests the raw Whisper output alongside the official protocols to refine misrecognitions, mainly named entities. Second, a separate GPT-4o pass evaluates each refined segment for semantic completeness. We filter out any segments whose Predicted BLEU score (derived from Whisper's average token log-probability) and GPT-4o evaluation score fall below a certain threshold. The final corpus contains 801 hours of audio, of which 555 hours pass our quality control. Compared to the original sentence-level SPC release, our long-form dataset achieves a 6-point BLEU improvement, demonstrating the power of combining robust ASR, LLM-based correction, and data-driven filtering for low-resource, domain-specific speech corpora.