Introducing microphone calibration techniques for reliable loudness estimation in the CFDA tests

Abstract

This study reports on the implementation of low-cost microphone calibration procedures to ensure that volume levels of digital audio recordings are of similar intensity (loudness) to the actual speech utterances that they represent. In the context of this investigation, these utterances are produced by patients as they attempt the various articulation exercises of the Computerised Frenchay Dysarthria Assessment (CFDA) diagnostic test suite. In fact, these calibration procedures are designed to normalize the signal intensity of CFDA-recorded audio samples so that two audio recordings which produce the same volume readings will actually be of the same perceived loudness even though these recordings may have been made on different computers with different microphone and sound card configurations. It is demonstrated that the aforementioned calibration procedures are fit for purpose in the context of pure tones, but less so for speech-like noise which is more complex in its tonal qualities and composition. Nonetheless, the proposed calibration procedures have consistently produced a close similarity in signal energy between “live” utterances and their corresponding digital recordings. This consistent similarity in energy has been deemed by a panel of expert clinicians to be a substantial improvement over the previous CFDA calibration protocols.