From an article by Oliver Masciarotte in Mix, Sept. 2002, p. 97-98:
"One of the new additions to the MPEG-4 audio toolbox, along with
long-term prediction and bit-rate scaleability tools, is Perceptual
Noise Substitution, or PNS, a feature designed to further optimize
bit rate efficiency.
"PNS is based on the observation that, perceptually, all noise sounds
about the same. This means that the actual fine structure of a noise
signal isn't that important. Rather, the bitstream just transmits a
region of frequencies as noise-like; additional information defines
the total power in that band. In the decoder, a randomly generated
noise will be inserted into the appropriate spectral region according
to the power level."
Hmmm. We've known that ever since we faked crowd sounds by exhaling
into a resonance between our hands. Will this technique wipe out soft
sounds or reverb tails sinking into a noise floor? Will it
substitute pink noise for a subtle ambience? Is this feature
something that an encoder can use or not use?
-Dan Dugan
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