This supplement provides preliminary audio performance requirements for telephones capable of transmitting an audio bandwidth extending beyond the conventional telephony bandwidth of 300 to 3400 Hz, to a bandwidth of approximately 150 to 7000 Hz. Such telephones are known as wideband audio telephones, and will make use of digital encoding schemes such as Recommendation G.722.Wideband audio represents a considerable departure from traditional telephony, offering significantly improved quality. However, since this is a new technical area, the requirements in this supplement are not complete, and studies are on-going. Guidance on making wideband audio measurements may be found in the Annex A to this supplement.