Quality improvement of telephone speech by artificial bandwidth expansion - listening tests in three languages

Quality and intelligibility of narrowband telephone speech can be improved by artificial bandwidth expansion (ABE), which expands the speech bandwidth using only information available in the narrowband speech signal. This paper describes an ABE method that generates a high-band expansion using spectral folding and then modifies the magnitude spectrum of the expansion band with spline curves. The performance of the ABE algorithm was evaluated by formal listening tests in three languages: American English, Russian, and Mandarin Chinese. The results of the listening tests indicate that ABE-processed speech was preferred to narrowband speech in all tested languages.