If there’s one thing we’ve learned over the years it’s that plenty of people will happily sacrifice audio quality for convenience. The popularity of music streaming services and wireless headphones are proof of that. Although seldom a match for a well-recorded LP or good pair of wired headphones, they sure are mighty handy.
Recently, however, there has been a conscious push-back for quality. The vinyl resurgence has demonstrated as much – LPs certainly aren't lauded for their convenience – and so has the rise of high-resolution audio. So is there a way to enjoy ease of use without sacrificing performance?
The folks at telecommunications giant Qualcomm certainly think so. In January 2016, the company launched aptX HD, a Bluetooth codec capable of wirelessly transmitting 24-bit hi-res audio between aptX HD-supporting kit – and the closest-in-quality rival to Sony's high-quality LDAC codec. In a nutshell, Bluetooth devices such as portable speakers, smartphones and wireless headphones can now sound even better because of it.
aptX HD isn't the newest or most advanced of Qualcomm's Bluetooth connections – that'd be aptX Adaptive and aptX Lossless – but it is the most prevalent in hardware right now, and probably will be for some time.
So, what's so good about aptX HD? How can you hear it? And what devices are compatible? Let's get to it...
First, what is aptX Bluetooth?
To understand what aptX HD is, we need to discuss what ‘classic’ aptX is. It is an audio-coding algorithm, created in the late 1980s, popular with film studios and radio broadcasters. Steven Spielberg was an early adopter, collaborating to use aptX to record audio for 5.1 digital playback for films including Jurassic Park in 1993, and later Schindler’s List and Saving Private Ryan.
These days, aptX is synonymous with Bluetooth, which you’ll find on plenty of computers, smartphones, AV receivers, and plenty of other consumer electronics products.
What’s the big deal about aptX? Its party trick is the ability to transmit music, full bandwidth, at a ‘CD-like’ 16-bit/44.1kHz. Note that it is ‘CD-like’ and not ‘CD-quality’ because aptX uses compression (which helps to reduce audio-coding delays and minimise latency issues) and therefore, like most other Bluetooth codecs out there, is not lossless. It's also designed to sound better than standard Bluetooth. Classic aptX has a compression ratio of 4:1 and a data rate of 352kbps.
- Here's everything you need to know about high-resolution audio
What is aptX HD?
Now for aptX HD, which is essentially an updated, beefed-up aptX with the ability to transfer music in a way that permits better sound quality.
It was released in reaction to the increasing popularity of hi-res audio and supports audio at 24-bit/48kHz. Compression remains at a ratio of 4:1, with a bitrate of 576kbps.
Whether it is a match for a wired hi-res signal is debatable, and straightforward comparisons are tricky as you can't turn aptX HD on or off on products as a means of discerning differences in sound quality, but Qualcomm is boldly gunning for ‘better-than-CD’ sound quality here with its wording. And there are plenty of class-leading headphones we've heard, such as the Sony WH-1000XM3, Bowers & Wilkins PI3 and Beyerdynamic Amiron Wireless, that use it.
Interestingly, aptX HD is missing from the spec sheet of the newer Sony WH-1000XM4 – our current favourite wireless headphones – in favour of Sony's own LDAC codec, which allows high-res audio streaming over Bluetooth at up to 990 kbps at 24 bit/96kHz – higher than aptX HD. More on that later.
- Read all about Sony's LDAC: what is it? aptX vs LDAC
What do you need to hear aptX HD?
There are requirements for using aptX HD. First, you need the right hardware. Specifically, we’re talking devices that contain one of Qualcomm's compatible Bluetooth audio SOCs (system on chips).
Not only can they handle end-to-end 24-bit audio; they also provide greater digital-signal processing than their predecessors. Qualcomm promises a lower signal-to-noise ratio through encoding and decoding, as well as less distortion too, particularly in the 10-20kHz range.
The requirement for a specific chipset means you will get aptX HD only if you have the right devices in the first place: there is no option for a software upgrade later, nor is there any scope for any sort of audio ‘upscaling’.
The good news, however, is that you don’t need to worry about backward/future compatibility, as aptX HD devices are compatible with ‘classic’ aptX headphones and speakers.
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Which products support aptX HD?
Android smartphones and tablets were some of the first products to implement aptX HD since its launch, with the LG G5 being the very first smartphone to adopt it. Other LG phones quickly followed – and support is now fairly common across various phones from Sony, OnePlus and Google. That includes the latest Sony Xperia 1 III, OnePlus 9 Pro and Google Pixel 6 flagship handsets.
Notable exceptions include Apple's iPhones – they don't support the aptX codec at all – while Samsung's recent generations of Galaxy and Note devices (including the new Galaxy S22 handsets) support aptX but not aptX HD. Baffling.
But now aptX HD isn't just in headphones but everywhere – in headphones, wireless systems, music streamers and even a Cambridge Audio turntable.
When it comes to portable music players, Astell & Kern is the most prominent supporter of aptX HD alongside Sony's Walkman. For example, the Award-winning Astell & Kern A&norma SR25 (and its MKII version) and A&futura SE200 players are compatible with the codec.
Beyerdynamic's excellent Xelento Wireless, Aventho and Amiron Wireless headphones support aptX HD too, as do Sony's WH-1000XM3 and WH-XB900N. As for Bowers & Wilkins, its PX, PX7 and Pi3 headphones are all aptX HD certified, as are its latest PI7 true wireless earbuds.
Adoption on the hi-fi side has been growing too. Supporters include (but aren't limited to) Naim's Uniti Star, Atom, Nova streaming music systems; Cambridge Audio's Edge A and Edge NQ amplifiers and Evo 75 and Evo 150 streaming systems; the Dali Callisto and Oberon all-in-one speaker systems; Bowers and Wilkins' Formation Duo and other Formation products. The Ruark R5 desktop system comes with aptX HD built-in, as does the NAD C 658 music streamer.
Want to add aptX HD to your existing setup? Check out the iFi Zen Blue, which can add offline streaming to your system.
We could go on, but we'll leave you to scour the spec sheets of the product(s) you're interested in (or browse the full list of 300+ products that support aptX HD here (opens in new tab)). The point is, aptX HD is continuing to gain traction.
aptX HD vs LDAC
So how does aptX HD stack up against its close codec rival, LDAC? Sony's LDAC codec is technically the most efficient codec with a higher data rate. LDAC allows you to stream high-resolution audio up to 32-bit/96kHz over Bluetooth at up to 990kbps, compared to aptX HD's 24-bit/48kHz support at 576kbps.
(For context, the newer aptX Adaptive, meanwhile, supports up to 24-bit/96kHz and scales dynamically between 279kbps and 420kbps, while the latest aptX Lossless (which is part of Qualcomm's new Snapdragon Sound package) promises lossless CD-quality (16-bit/44.1kHz) audio over Bluetooth at a rate of "beyond 1Mbit/s".)
As is the case with LDAC, you still need the right hardware with the relevant chip to take advantage of the codecs. And the fact that hardware rarely tends to support both codecs makes it tricky to compare the two.
What about aptX Adaptive and aptX Lossless?
But while the most accessible right now, aptX HD isn't actually the pinnacle of Qualcomm's Bluetooth technologies today. In 2018, Qualcomm unleashed a newer generation of Bluetooth codecs, aptX Adaptive.
aptX Adaptive, which may well replace aptX HD in time, essentially combines the current aptX HD with aptX Low Latency, a codec that boasts audio and video syncing with less than 40 milliseconds of latency when you’re watching a video or playing a game on your connected device.
Backward-compatible with aptX and aptX HD, aptX Adaptive takes into account the external RF environment around your aptX Adaptive device, so you shouldn't experience any drop-outs when you're taking your phone out of your pocket or bag. It will automatically optimise audio depending if you’re making calls or listening to music, too.
As the name suggests, aptX Adaptive is a codec designed to be capable of adapting. Rather than having a locked bitrate like aptX Classic, Low Latency, and aptX HD, the newest version of the codec can dynamically scale the bitrate to adapt and adjust quality.
A quick glance at the numbers might look disappointing. aptX Adaptive’s bitrate scales between 279kbps and 420kbps for CD and hi-res quality music – much lower than the 352kbps and 576kbps of aptX Classic and HD respectively – but Qualcomm says that the codec is simply much more efficient than the previous version.
The best part, though, is that while Qualcomm launched aptX Adaptive in 2018 with 48kHz support, the codec is actually capable of wirelessly transmitting 96kHz files – the sampling rate studio music is often recorded and, as digital hi-res files, distributed at. So far, over 100 products support aptX Adaptive, including Bowers & Wilkins' latest slew of headphones and Zeppelin wireless speaker; the most recent B&O, Yamaha, Beyerdynamic and PSB headphones; the iFi Zen Blue receiver; and the latest Sony Xperia phones.
But that's not where this story ends. Oh no. Qualcomm has announced recently that it has gone one better with aptX Lossless. This latest codec is not only capable of 96kHz support (with transmission bitrate scaling dynamically from 279kbps up to 860kbps) but also lossless transmission at CD quality (16-bit/44.1kHz) – an unprecedented feat within the Bluetooth audio world.
aptX Lossless is a brand-new feature of the 2021-announced Snapdragon Sound audio platform and is essentially the result of Qualcomm optimising a number of wireless connectivity and audio technologies within aptX Adaptive. We can expect to see aptX Lossless-supporting products emerging this year.
Until then – or until Sonos or Apple find a way to transmit hi-res audio losslessly over a Bluetooth alternative, as they're rumoured to be looking into – aptX HD is an excellent and accessible way to stream music in high quality over Bluetooth between devices.
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