Codecs explained

All Bluetooth audio must be compressed and converted to some extent before it can be streamed to your headphones. As things stand, sending uncompressed sound requires too much bandwidth. The codecs used for this have improved a great deal, and as well as AAC and SBC there’s now aptX and HD, supported by many of the models on test, that improve sample and bit rates along with the reliability of the stream. Some use the LDAC codec, which transmits at a higher bit rate.

Although higher data rates are preferable, they’re only one part of the signal chain. A “simple” AAC stream still sounds good, and it’s things like the design of the cups and the tuning of the drivers that also play a big role in how headphones sound. Most models on test support wired listening as well as wireless, where codecs aren’t in use at all.