Bandwidth extension of telephone speech using a filter bank implementation for highband MEL spectrum

The limited audio bandwidth used in telephone systems degrades both the quality and the intelligibility of speech. This paper presents a new method for the bandwidth extension of telephone speech. Frequency components are added to the frequency band 4-8 kHz using only the information in the narrowband speech. First, a wideband excitation is generated by spectral folding from the narrowband linear prediction residual. The highband of this signal is divided into four subbands with a filter bank, and a neural network is used to weight the subbands based on features calculated from the narrowband speech. Bandwidth-extended speech is obtained by summing the weighted subbands and the original narrowband signal. Listening tests show that this new method improves speech quality compared with a previously published bandwidth extension method.