aptX

aptX is a family of proprietary audio codecs for Bluetooth wireless audio transmission, developed by CSR and now licensed by Qualcomm. The aim is to deliver higher fidelity than the baseline SBC codec by using efficient compression and psychoacoustic modeling, so that devices with aptX support can achieve closer to CD-quality sound over Bluetooth when both transmitter and receiver implement the codec.

The original aptX encodes 16-bit PCM at common sampling rates such as 44.1 or 48 kHz and compresses it to a fixed data rate that improves perceived audio quality while keeping latency relatively low compared with SBC. Over time, Qualcomm has expanded the family with variants designed for higher resolution, lower latency, or more adaptable performance.

aptX HD extends the format to support higher fidelity, including 24-bit audio and higher-quality streaming, preserving more dynamic range and detail than the original. aptX LL, or low latency, is engineered to minimize delay between the source and playback, typically reducing end-to-end latency to a level suitable for video and gaming applications.

aptX Adaptive is a dynamic variant that adjusts bitrate in real time to balance audio quality and latency based on link conditions. There is also aptX Lossless, promoted as a path toward transparent, bit-for-bit identical audio under Bluetooth constraints, and aptX Voice, optimized for clear speech in telephony by using a voice-focused encoding.

Adoption and licensing: aptX is a licensed, proprietary codec. Support varies by device and platform; many Bluetooth audio devices and smartphones include aptX support, though competing codecs (such as SBC, AAC, LDAC, and LC3) are also common.