Sp-3-4350. 120-rv3 (to become ansi/tia-470. 120-C) Draft 22a ast ballot Comments with track changes on Telecommunications Telephone Terminal Equipment Transmission Requirements for Analog Speakerphones
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- (Normative) – Calculation of Loudness Ratings
Receive Noise CurveThe A-weighting curve is defined in ANSI S1.4-1983 (Reaff. 2001) Table A.3 – A-weighting curve
Figure A.2 – A-weighting noise weighting curve
This Annex details the loudness rating calculations and weighting factors relevant to this document. Loudness ratings are used to insure that the loudness of a connection from the Mouth Reference Point (MRP) of the talker to the Ear Reference Point (ERP) of the far end listener is at a satisfactory level. The loudness of the complete path is designated as the Overall Loudness Rating (OLR). The MRP to electrical component is referred to as the Send Loudness Rating (SLR). The electrical to ERP component is the Receive Loudness Rating (RLR). The loudness of the sidetone path of handsets and headsets is referred to as the Sidetone Masking Rating (STMR). Loudness ratings are used rather than simple level measurements because of better subjective correlation. Loudness ratings more closely account for changes in the ear’s sensitivity at different frequencies and its nonlinear response to varying sound levels. The following calculations are based on the 1999 revision of ITU-T Recommendation P.79. Older versions of P.79 should not be used. ITU-T P.79 provides information on the derivation of the loudness rating algorithm. For use in these loudness ratings formulae, frequency response measurements shall be converted to the R10 format, by using band averaging according to IEEE Std 269. At each ISO R10 preferred frequency 
where
H’(f) = response at the new preferred ISO R10 frequency f = preferred ISO R10 frequency N = number of response values within the 1/3 octave band centered at f i = index for each response value within the 1/3 octave band Hi = measured response value (in dB) For the lowest frequency within the band, i = 1. For the highest included frequency, i = N. The 1/3 octave pass band limit frequencies can be calculated according as: 
Where n is the band number.
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