A network interface device connectable to a network, the device being arranged to receive digital audio data representing an audio signal and, substantially in real time, to launch data packets representing the digital audio data onto the network, the device comprising: an attribute detector arranged to generate attribute data representing an attribute of the audio signal; and a packetiser operable: to format the digital audio data into audio data packets to be launched onto the network; and to format the attribute data into attribute data packets, separate from the audio data packets, to be launched onto the network.