aptX HD is a variant of the aptX codec, designed specifically for high-definition audio. It supports 24-bit/48 kHz audio transmission, with a maximum bitrate of 576 kbps. While not truly lossless, aptX HD offers a significant improvement over standard SBC, with a more detailed and nuanced sound.

LDAC, on the other hand, is a proprietary codec developed by Sony. It supports 24-bit/96 kHz audio transmission, with a maximum bitrate of 990 kbps. LDAC is designed to provide a more accurate and detailed sound, with a focus on preserving the dynamic range and frequency response of the original audio signal.

Both aptX HD and LDAC offer a superior listening experience compared to standard SBC, but they still don’t quite match the quality of wired connections or true lossless audio transmissions.