noise shaping definition communications Spectral noise
transformation in a quantisation processes. Noise is "colourised" in the time domain
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.