Transmitting stereo signals via the Bluetooth protocol from a smartphone, tablet or other audio source to a powered speaker, vehicle sound system or other receiver. A2DP (Advanced Audio Distribution Profile) The Bluetooth stereo protocol is A2DP, which differs from the Bluetooth commonly used for cellphone-to-headset transmission. A2DP removes even more data from MP3 files, which are already highly compressed (see SBC); however, other Bluetooth codecs actually improve the sound quality (see aptX). For Bluetooth categories, see Bluetooth profiles. See Bluetooth speaker, AAC, MP3 and Wi-Fi audio.