A family of audio codecs from CSR plc, Cambridge, England (www.csr.com) that are designed to improve the quality of wireless audio transmission. Introduced in the 1990s as a DSP chip, aptX products are both hardware and software encoders for personal computers, radio and live broadcasting, wireless microphones and Bluetooth speakers and headphones. This entry summarizes aptX for Bluetooth stereo transmission, known as the Bluetooth Advanced Audio Distribution Profile (see Bluetooth audio). AptX for Bluetooth Speakers and Headphones The aptX codec is found in smartphones, tablets and Bluetooth speakers in order to provide better sound than the standard Bluetooth SBC music codec, which degrades audio quality. Both sending and receiving devices must be aptX enabled; for example, aptX is used in many Android smartphones and tablets, as well as Mac computers, but not in Apple mobile devices. In 2013, aptX Low Latency for Bluetooth added enhancements to ensure that the audio stays in sync with the video when users watch movies and play games using aptX-enabled Bluetooth headphones. Why aptX is Better for MP3 Files When an aptX device is handed an MP3 file to transmit, it first decompresses the format back to the original 1.411 Mbps bit rate of the original linear PCM CD track. It then compresses this "baseband" bitstream to 352 Kbps via adaptive differential PCM (ADPCM) without any change to the music data. The result is a non-destructive format compared to the standard SBC codec used in Bluetooth stereo (see Bluetooth audio). See ADPCM, SBC and Kleer.