Neural network-based artificial bandwidth expansion of speech

The limited bandwidth of 0.3-3.4 kHz in current telephone systems reduces both the quality and the intelligibility of speech. Artificial bandwidth expansion is a method that expands the bandwidth of the narrowband speech signal in the receiving end of the transmission link by adding new fiequency components to the higher frequencies, i.e., up to 8 kHz. In this paper, a new method for artificial bandwidth expansion, termed Neuroevolution Artificial Bandwidth Expansion (NEABE) is proposed. The method uses spectral folding to create the initial spectral components above the telephone band. The spectral envelope is then shaped in the frequency domain, based on a set of parameters given by a neural network. Subjective listening tests were used to evaluate the performance of the proposed algorithm, and the results showed that NFABE speech was prefered over narrowband speech in about 80% of the test cases.