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Convention Paper

Minimally Audible Noise Shaping

Authors: Lipshitz, Stanley; Vanderkooy, John; Wannamaker, Robert A.

AES Convention 88 · Paper 2916 · March 1990

Abstract

Normal quantization or requantization noise is white, but the ear's sensitivity to low-level broadband noise is not uniform with frequency. By adopting a suitable weighting curve to represent low-level noise audibility, one can design dithered requantizing noise shapers to approximate the inverse of the audibility curve and hence achieve the least audible noise penalty. If Fielder's modified E-weighting curve is adopted as a model of the 15-fon audibility curve, a reduction of 10.9 dB in perceived noise is possible by the use of a simple second-order noise shaper. This result is already within 0.6 dB of the theoretical minimum set by information theory, and almost a 2-bit gain in apparent signal-to-noise ratio. Even greater perceived noise reductions are possible if one adopts an audibility weighting curve which more closely approximates the ear's precipitous high-frequency rolloff, and incorporates a higher-order filter into the noise-shaper's feedback loop. In face, a 20-dB apparent reduction in the requantizing noise is then possible with filters of modest order, but the penalty is a significant increase in the total noise power. This paper explores these questions and illustrates some of the available options. Such noise shaping will soon get advantageous in order to preserve on the 16-bit compact disc the lower noise floor of an original 18- or 20-bit master recording.

Details

Published in
AES Convention 88
AES Convention
88
Paper number
2916
Publication date
March 6, 1990
Session subject
Digital Audio
Affiliation
Audio Research Group, University of Waterloo, Waterloo, Ontario, Canada (See document for exact affiliation information.)
Type
Convention Paper