Abstract: A communication system comprises a transmitter unit (10, 60) arranged to be carried by or located near a user, and an earpiece including a receiver unit (30, 70), the system operating with a carrier frequency of less than 100 kHz, preferably less than 30 kHz, most preferably in the range 14 to 20 kHz. The system employs vestigial sideband modulation by cutting off part of an upper sideband. The received signal is digitized and then sampled to an envelope-tracking sampled-data root-filter square detector (40) configured as a digital signal processor.

Abstract: A communication system comprises a transmitter unit (10, 60) arranged to be carried by or located near a user, and an earpiece including a receiver unit (30, 70), the system operating with a carrier frequency of less than 100 kHz, preferably less than 30 kHz, most preferably in the range 14 to 20 kHz. The system employs vestigial sideband modulation by cutting off part of an upper sideband. The received signal is digitized and then sampled to an envelope-tracking sampled-data root-filter square detector (40) configured as a digital signal processor.

Abstract: An ear tip or ear plug (20) comprises a body portion (21) having flexible peripheral rib elements (23, 24, 25) projecting therefrom to provide a comfortable and secure fit in a wearer's ear. The rib elements are between 0.2 mm and 2 mm high, preferably 1 mm. The body portion (21) is also flexible and may be made integrally with the rib elements by an injection-moulding process. The body portion (21) has a generally bulbous shape, having a substantially elliptical cross-section and a longitudinal axis (28) which is curved or bent to one side. A conduit (30) may extend between exterior end (38) and interior end (39).