A noise weighting established by the International Consultative Committee for Telephony (CCIF, which became CCITT and, more recently, ITU-T,) designated as CCIF-1951 weighting, for use in a noise measuring set or psophometer. Note: The shape of this characteristic is virtually identical to that of F1A weighting. The psophometer is, however, calibrated with a tone of 800 Hz, 0 dBm, so that the corresponding voltage across 600 ohms produces a reading of 0. 775 V. This introduces a 1-dBm adjustment in the formulas for conversion with dBa.