A new one-third-octave-band noise criteria (NC) rating method is presented. one-third-octave-band NC curves from NC 70 to NC 0 are derived from the existing octave-band curves, adjusted for bandwidth, fit to continuous functions, and redistributed progressively over this space. This synthesis is described in detail. The diffuse field hearing threshold at low frequencies is also derived. Several NC curves at high frequencies are shown to be below threshold (inaudible). NC ratings are calculated using both the new one-third-octave-band and the legacy octave-band methods for a number of different room noise spectra. The resulting values were found to be similar for both methods. NC ratings using the new 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 the 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.
