Sending loudness rating
The sending loudness rating is a measure of the loudness of the transmit audio sent through the microphone of a communication device It compares the Sound intensity of the sound waves into the microphone to the resulting audio signal. It is measured in dBV/Pa.
For telephony, the reference sound pressure level is 20 micro-Pascals, with values in dB referenced to that value.
20 micro-Pascals is called the Threshold of human hearing, and is equal to 0 dB Sound pressure level.
ITU-T recommendation P.79 has the frequency weighted sensitivity calculations in it for sending loudness rating and receive loudness rating for telephony.
