I received this reply from JJ Profitt on the pro-audio list:
PNS is an encoder option. It may be used, it does not have to be used. How
it works when it is used depends greatly on the ability of the encoder to do
it right.
It's not in common use in any encoder I know of. Control and calculation of
how to use it is nasty and difficult.
JJ
> -----Original Message-----
> From:
> On Behalf Of Dan Dugan
> Sent: Monday, May 05, 2003 6:39 PM
> To:
> Cc: Nature Recordists
> Subject: [ProAud] "noise substitution" in MPEG-4 audio (AAC)
>
>
> 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
> ==For info on Pro-Audio, send 'info pro-audio' to
> ===
>
==For info on Pro-Audio, send 'info pro-audio' to ===
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