noise shaping

communications Spectral noise transformation in a

quantisation processes. Noise is "colourised" in the timedomain an/or frequency domain by adding parts of the

previous sample. The SNR bandwidth and SNR time integral

stay the same, so some noise decreases, some increases, but

overall noise always increases.

An example of noise shaping in the frequency domain is

quantisation of samples on a Compact Disc to reduce noise

below -98 dB. The are different algorithms with slightly

different filters, e.g. Super Bitmapping, 4D Recording.

A time domain example is MPEG-4 AAC TNS, which is a method

to enhance quality by temporal forming of the noise in a

transform block.

(2003-07-19)