Maximization of the subjective loudness of speech with constrained amplitude

Abstract

We introduce an adaptive algorithm for constraining the amplitude of speech signals while at the same time trying to maintain the subjective loudness and trying not to produce disturbing artifacts. The algorithm can be applied to compensate for the clipping distortion of amplifiers in speech reproduction devices. The algorithm analyzes the speech signal on multiple frequency bands and applies an internal audibility law in order to make inaudible changes to the signal. An example of the audibility law, presented in the form of a matrix, is described, associated with a specific speech reproduction device. Multiple band-pass signals are processed with a waveshaper to accomplish soft-clipping and to constrain the amplitude of the processed signal. When processed with the proposed algorithm, the computational loudness value of speech signals was found to diminish only slightly (approximately 6 sones) during processing, while at the same time the signal amplitude could be reduced by even 15 dB.