Hearing aid, relay device, hearing-aid system, hearing-aid method, program, and integrated circuit

A hearing aid which outputs, to a user, a sound obtained from a transmission audio signal obtained from one of external apparatuses, the respective external apparatuses outputting propagation sounds that propagate in air and transmit, on a first transmission path, transmission audio signals that include the transmission audio signal and correspond one-to-one to the propagation sounds, said hearing aid comprising:

• a sound collecting unit configured to collect one of the propagation sounds output from the respective external apparatuses;
• a receiving unit configured to receive the transmission audio signals transmitted from the respective external apparatuses;
• a comparing unit configured to compare the propagation sound collected by said sound collecting unit with each of the transmission audio signals received by said receiving unit, and select one of the transmission audio signals that corresponds to the propagation sound;
• and
• a sound output unit configured to output, to the user, the sound obtained from the transmission audio signal selected by said comparing unit.