Focussing on the prosodic labelling of Japanese as an example, this paper describes the application of speech synthesis technology in a variety of speech processing tasks. It discusses first the use of synthesised utterances in the forced alignment and segmentation of a speech corpus, then the use of generated prosodic contours to determine the prosodic phrasing of an utterance, and finally the comparison with speech resynthesised using the prosodic transcription of the original utterance in order to check the transcription. It closes with an analysis of results from an auto-transcription of Japanese ToBI, and discusses some limitations of the proposed J-ToBI system.