A proposal for a new noise criteria (NC) method in 1/3 octave bands to supersede the legacy ASA/ANSI S12.2-2019 octave band metric is presented. 1/3 octave band NC curves from NC 65 to NC 5 are derived from the existing octave band curves, adjusted for bandwidth, fit to continuous functions, and redistributed progressively over this space. The proposed 1/3 octave band NC 0 contour is based upon the diffuse field hearing threshold at low frequencies and parallels the existing NC curves at high frequencies. This synthesis is described in detail. NC values are calculated using both the proposed and legacy methods for a number of different room noise spectra. The resulting values were found to be similar for both methods. NC ratings using the proposed method are particularly applicable to very low noise level critical listening environments such as recording studios, scoring stages, and cinema screening rooms, but are shown to also be applicable to higher noise level environments. The proposed method better tracks audibility of noise at low levels as well as the audibility of tonal noise components, while the legacy method as originally conceived generally emphasizes speech interference.

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