Perceptual Noise Substitution
Part of the MPEG-4 Standard ISO/IEC 14496-3 Audio (MPEG-4 General Audio) and not available within MPEG-2 AAC i.e. PNS is one of the new tools introduced in MPEG-4 AAC.
Based on the fact that the exact spectral components of noise in audio signals is not perceptible, hence the original noise can be substituted by randomly generated noise over an appropriate spectral region at an equivalent power level during decoding, i.o.w. "noise always sounds the same¨.
- MPEG-4 Advanced Audio Coding by Peter Doliwa, http://web.archive.org/web/20060206183237/http://www.ibr.cs.tu-bs.de/courses/ss04/skm/mpeg-4-aac.pdf