Automatic determination of stability and validity of Speech Transmission Index measurements

Abstract

The Speech Transmission Index (STI) uses the modulation transfer function to characterize speech communication channels with a single index. This index accurately predicts speech intelligibility. In order to measure the STI, a device or software is needed that utilizes an artificial test signal to estimate the modulation transfer function, and to derive the STI from that function. In practice, many STI measurements are found to be invalid and inaccurate, for two reasons: (1) the measurements are carried out in test conditions for which by design the STI is not intended; (2) equipment is used that does not meet specifications and requirements. A procedure is described to automatically verify if conditions for obtaining valid STI results are met. If possible, corrections are applied to compensate for incorrect settings and poorly adjusted measuring equipment. If automatic correction of the problem is not possible, then a warning is generated.

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