New objective measures for the evaluation of pitch extractors

Abstract

In this research, we developed and tested a variety of new objective measures for automatically evaluating pitch extractors for use in narrowband speech coders. For automatic computation of an accurate, reference pitch contour required by the objective measures, we modified an existing algorithm that uses the subglottal signal recorded simultaneously with the speech signal. To test and validate the objective measures, we conducted formal subjective speech quality tests, which involved five pitch extractors; a specially selected speech database of sentences that are likely to cause pitch and voicing errors; and two 2.4 kbit/s speech coders, the LPC coder and the harmonic deviations coder, each operating in clear or no noise and in Air Borne Command Post noise. Results obtained by correlating the objective scores with the mean subjective rating scores show that several of our objective measures produce consistently excellent correlation (0.9 - 0.995) for both coders and under both acoustic background conditions.