NOTE – The psophometer incorporates a weighting network, the characteristics of which differ according to the circuit under consideration, commercial telephone or sound program transmission circuits. The psophometric weights correspond to the aural effect of disturbing voltages of various frequencies. The psophometer recommended by the CCITT is defined in the CCITT Recommendation 0.41 from the Fascicle IV-4 of the Blue Book, 1989, for telephony, in the CCITT Recommendation J.16 from the fascicule III.6 of the Blue Book, 1989, for sound program channels.