Miipher-2: A Universal Speech Restoration Model for Million-Hour Scale Data Restoration

TL;DR

Miipher-2 is a scalable, language-agnostic speech restoration model that efficiently cleans large-scale multilingual datasets without explicit conditioning, improving data quality for training large generative models.

Contribution

It introduces a universal, conditioning-free speech restoration approach that operates efficiently on massive datasets using a pre-trained USM and parallel adapters.

Findings

Outperforms conventional SR models in multiple metrics

Operates in real-time on consumer-grade hardware

Successfully processes million-hour scale datasets

Abstract

Training data cleaning is a new application for generative model-based speech restoration (SR). This paper introduces Miipher-2, an SR model designed for million-hour scale data, for training data cleaning for large-scale generative models like large language models. Key challenges addressed include generalization to unseen languages, operation without explicit conditioning (e.g., text, speaker ID), and computational efficiency. Miipher-2 utilizes a frozen, pre-trained Universal Speech Model (USM), supporting over 300 languages, as a robust, conditioning-free feature extractor. To optimize efficiency and minimize memory, Miipher-2 incorporates parallel adapters for predicting clean USM features from noisy inputs and employs the WaveFit neural vocoder for waveform synthesis. These components were trained on 3,000 hours of multi-lingual, studio-quality recordings with augmented degradations, while USM parameters remained fixed. Experimental results demonstrate Miipher-2's superior or comparable performance to conventional SR models in word-error-rate, speaker similarity, and both objective and subjective sound quality scores across all tested languages. Miipher-2 operates efficiently on consumer-grade accelerators, achieving a real-time factor of 0.0078, enabling the processing of a million-hour speech dataset in approximately three days using only 100 such accelerators.