Digital audio can be transferred between a portable media player and an accessory. In one embodiment, an interface protocol is used to determine the sample rate capabilities of an accessory, allowing digital audio data for a track to be transmitted to the accessory at a sample rate supported by the accessory. When the sample rate of an audio track is not supported by the accessory, the media player can convert the sample rate of the track to a rate supported by the accessory and transmit the track after conversion. The media player also can use the interface protocol to inform the accessory if the sampling rate should be changed, e.g., due to tracks having different sample rates. The accessory then can send a request to the media player to change the sample rate. The media player then can transmit the digital audio data using the new sample rate.