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.