Yeah, it's the FM part. With A2DP it is possible to send an untouched MP3/AAC bitsteam between two devices. That's provided the transmitter has access to the original file data, and the receiver supports that codec. In most cases the audio is decoded into PCM, and then re-encoded into SBC, which all A2DP devices must support, so quality suffers. SBC is roughly based upon MPEG Audio-Layer II, or MP2, which I doubt many of you have ever seen. It's best suited to voice (just not male, German voices, as found my the Fraunhofer Institute).
