An audio system comprises a master device; a slave device; and a wired connection, suitable for connecting the master device and the slave device, and having at least two wires. In order to compensate for a round-trip transmission delay, a method comprises: transmitting a master clock signal on a first wire of the two wires, from said master device to said slave device; transmitting a synchronisation data pattern on a second wire of the two wires, from said slave device to said master device, wherein said synchronisation data pattern comprises signal level transitions at timings that are set based on a delay value stored in said slave device; in said master device, determining timings of said signal level transitions as received at said master device; transmitting, on the second wire, from said master device to said slave device, timing delay control data based on said determination; and in said slave device, receiving said timing delay control data; and updating said stored delay value based on said timing delay control data.