Normal quantization or requantization noise is white, but the ear's sensitivity to low-level broad-band noise if not uniform with frequency. By adopting a suitable weighting curve to represent low-level noise audibility, one can design dithered requantizing noise shapers to approximately 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-phon 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 fact, 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. These questions are explored and some of the available options illustrated. Such noise shaping will soon be advantageous in order to preserve on the 16-bit Compact Disc the lower noise floor of an original 18- or 20-bit master recording.
Click to purchase paper as a non-member or you can login as an AES member to see more options.
No AES members have commented on this paper yet.
To be notified of new comments on this paper you can
subscribe to this RSS feed.
Forum users should login to see additional options.
If you are not yet an AES member and have something important to say about this paper then we urge you to join the AES today and make your voice heard. You can join online today by clicking here.
