Graph-PIT: Generalized permutation invariant training for continuous separation of arbitrary numbers of speakers

TL;DR

Graph-PIT introduces a graph-based permutation invariant training method that allows continuous separation of an arbitrary number of speakers in meeting transcription, relaxing previous constraints and improving recognition accuracy.

Contribution

It proposes a novel graph-based PIT criterion that relaxes speaker number constraints, enabling processing of unlimited speakers and segments in continuous speech separation.

Findings

Improved recognition performance over uPIT on meeting data.

Can handle an arbitrary number of speakers and long segments.

Reduces computational effort by eliminating the need for complex stitching algorithms.

Abstract

Automatic transcription of meetings requires handling of overlapped speech, which calls for continuous speech separation (CSS) systems. The uPIT criterion was proposed for utterance-level separation with neural networks and introduces the constraint that the total number of speakers must not exceed the number of output channels. When processing meeting-like data in a segment-wise manner, i.e., by separating overlapping segments independently and stitching adjacent segments to continuous output streams, this constraint has to be fulfilled for any segment. In this contribution, we show that this constraint can be significantly relaxed. We propose a novel graph-based PIT criterion, which casts the assignment of utterances to output channels in a graph coloring problem. It only requires that the number of concurrently active speakers must not exceed the number of output channels. As a consequence, the system can process an arbitrary number of speakers and arbitrarily long segments and thus can handle more diverse scenarios. Further, the stitching algorithm for obtaining a consistent output order in neighboring segments is of less importance and can even be eliminated completely, not the least reducing the computational effort. Experiments on meeting-style WSJ data show improvements in recognition performance over using the uPIT criterion.