A device for transmitting a sound signal received from a source to an in-vehicle audio system includes sound input circuitry operable to receive a sound signal, control circuitry operable to convert the sound signal to a signal for transmission, and two transmitters both operable to transmit the signal for transmission to the in-vehicle audio system in a radio transmission channel. The control circuitry is also operable to change radio transmission channel by performing a frequency handover including changing from transmitting the signal for transmission from a first transmitter in a current channel to transmitting the signal for transmission from a second transmitter in a new channel.