Storage or transmission of audio signals is often subject to strict bitrate constraints. This is accommodated by audio encoders that encode the lower frequency part in a waveform preserving way and approximate the high frequency signal from the lower frequency data by using a set of reconstruction parameters. This so called bandwidth extension can lead to roughness and other unpleasant auditory sensations. In this paper, the origin of these artifacts is identified and an improved bandwidth extension method called Harmonic Bandwidth Extension (HBE) is outlined avoiding auditory roughness in the reconstructed audio signal. Since HBE is based on phase vocoders, and thus intrinsically not well suited for transient signals, an enhancement of the method by a novel transient handling approach is presented. A listening test demonstrates the advantage of the proposed method over a simple phase vocoder approach.
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