Bowers & Wilkins’ new range of wireless headphones and in-ears are the first to market using aptX Adaptive. So what’s that, then?

aptX Adaptive is a Bluetooth codec which aims to deliver the higher resolution of aptX HD in a more robust way, while also incorporating the advantages of aptX Low Latency, a codec which it will apparently replace.

It is also backwards-compatible with aptX & aptX HD, so that many existing phones will be able to use those codecs with devices specified as aptX Adaptive; for the full abilities you'll need to wait for phones which specifically support aptX Adaptive. 

aptX Low Latency has proven of particular use for gamers on headphones, and for viewing videos with the audio played over Bluetooth, where delays can cause lip-sync issues (or sudden death for gamers). Qualcomm, aptX’s owner, quotes low system latency of approximately 80ms, though that might still be enough to cause lip-sync issues for those sensitive to such delays.

(Startling fact: Qualcomm reckons that around 7 billion devices exist which are aptX-enabled...)

aptX Adaptive achieves its quoted 24-bit/48kHz streaming quality using remarkably low bit-rates, typically 279kbps to 420kbps, far below the actual 2304kbps of native 24/48 files.

This indicates that as with aptX HD the transmission is not lossless (confirmed by Qualcomm here). Lossless transmission can usually roughly halve a bit-rate while maintaining the file’s full integrity, so it seems that in aptX Adaptive a further lossy compression is used to drop the bit-rate to between and half and a third of that required for lossless 24/48.

Of course the lossiness would be significantly less when transmitting a CD-quality file at 16-bit/44.1kHz.

Since even the quoted lower rates can cause glitches in transmission in difficult areas with high RF, a further reduction will now happen on the fly, and this is the ‘Adaptive’ part of the new codec, designed to remove the occasional glitchiness of the fixed-rate aptX HD, which runs at 576kbps when at maximum quality.

“Dynamic bit-rate adaptation designed to ensure consistently robust audio streaming in challenging RF environments, based on handset user application focus without user intervention,” says Qualcomm.

We reckon that’s still significant lossy compression, especially if the Adaptive reduction kicks in without you knowing it. The question, then, is how much you will be able to hear. Qualcomm here offers a very interesting snippet in the form of a quote:

“No statistically significant difference between Qualcomm aptX Adaptive at 420kbit/s and Linear Audio at 24bit / 96kHz” - Salford University independent test results, June 2018.

So that’s Salford Uni in the UK, which has a legendary Electroacoustics department as well as the longest bar of any UK university, claiming no measurable let alone audible difference between the best level of aptX Adaptive and the native file.

This might seem quite the claim, except that we’ve been here before, when Sony’s Chief Sound Architect told us in a face-to-face that Sony could neither hear nor measure any difference between files of 256k up when played through Sony’s DSEE HX upscaling technology in comparison to a high-res version. The exceptions, he said, were dense high-information musical files, but these were rare.

This goes once again to the argument that high-res files are excessively large containers which are largely empty – memorably described by TAS’s Robert Harley as “like shipping a paperback book in a box the size of a filing cabinet”. The problem is you’re not sure exactly where the book is, so if you only have half the filing cabinet, you might miss some important bits of the book. Most of the time, on the other hand, you’ll not notice the difference.

And we reckon anything which improves the quality of wireless Bluetooth is to be welcomed.