1.1 S COPE This standard establishes telephone audio performance requirements, measurement methods, and test procedures for telephones with high receive gain and control of the receive frequency spectrum. This standard addresses audio performance in narrowband and wideband telephony frequencies using scientific methods and techniques derived or adapted from current telephone measurement standards for handsets and speakerphones.  Narrowband is defined as the frequency range between 300 and 3400 Hz.  Wideband is defined as the frequency range between 100 and 7000 Hz 1.2 C OMPLIANCE TO H EARING L OSS C ATEGORIES This standard provides performance requirements for three levels...