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aptX: The codec that gave Bluetooth teeth

An up to date look at aptX technology, both for the consumer and professional audio sectors

AptX, eh? A few years ago, an AES or IBC show wouldn’t go past without some update, feature extension or licensing deal involving the magical codec from Belfast being announced in the pages of PSNEurope. Then it all seemed to go quiet for a while… or did it?

Jonny McClintock begs to differ. He’s been involved with the aptX audio algorithm since 1993, initially as sales and marketing director and shareholder of APT Licensing, prior to the operation’s acquisition by CSR (a Cambridge-based semiconductor developer) in 2010. McClintock’s role at APT involved the licensing of aptX into the professional audio market sector, including digital cinema, radio broadcast, ADR, voice-overs, and stereo/5.1 mix approvals. Since joining CSR, and latterly Qualcomm (formally QTIL, or Qualcomm Technologies International, Ltd), which acquired CSR in April 2015, McClintock has been introducing aptX into Bluetooth to ensure the consistent transfer of high quality music.

Ahead of IBC and AES Los Angeles, McClintock approached PSNEurope in order to set the record straight about what’s been happening behind the scenes.

Let’s just make it clear to start with: what’s Qualcomm aptX audio?

JMcC: The aptX audio codec is an alternative to SBC (sub-band coding, the codec specified by Bluetooth) which preserves high sound quality in audio when transmitted over a Bluetooth connection. aptX is widely supported in high-performance Bluetooth equipment including headphones, headsets, automotive audio and home entertainment systems from over 320 leading audio brands.

What can you tell us about how it came to be?

The algorithm originated as the result of research undertaken at Queen’s University Belfast in the late 1980s. Back then, the work was focused on bit-rate reduction for wide-band stereo audio.

In more detail?

CD audio requires 1.411Mbit/s of data to transfer music sampled at 44.1kHz FS (full scale) – the use of aptX reduces this bit-rate to 354kBit/s. Thanks to these significant bit-rate efficiencies, aptX is also able to preserve audio quality and perform the mathematical process in an incredibly quick time: under two milliseconds. These simultaneous features were unknown in the ‘80s, and even today no other wide-band audio coding technique can deliver this holy grail of bit-rate reduction.

How has this Bluetooth codec impacted the professional audio scene?

For one thing, aptX was the first codec to enable digital surround sound and the low-frequency sound effects that make those thunderous booms possible in cinemas. Many big names in the film industry began using aptX to deliver the high quality audio, and effects that Hollywood demanded with aptX powering the sound for movies like /Jurassic Park/.

Then there was the standardisation with ISDN, when aptX was bundled with the digital dial-up telephone lines provided by telecoms companies. This enabled the film industry to standardise on aptX for multiple applications, such as mix approvals, voice-over, ADR and foreign language overdubs. As a result, thousands of theatres around the world could deliver consistently high quality audio.

I guess the final thing to mention is that the global radio broadcast industry became increasingly reliant on aptX during the 1990s and 2000s. They used it to deliver digital sound with near-CD quality. Over 30,000 radio stations worldwide, and thousands of cutting-edge film studios started using the aptX codec for high-quality audio delivery.

We’ve seen aptX on the packaging of many consumer audio products too. Is it the same technology?

Yes. In 2009 the aptX audio codec began to bring high-quality audio to wireless consumer electronics applications. This was actually kind of important for consumer audio because until then, Bluetooth Stereo had an unfortunate reputation for providing only average audio quality. aptX helped Bluetooth-enabled products overcome this barrier.

What about the recent developments? Especially since the completed acquisition of CSR by QTIL last year.

Well, the major development is aptX HD, our next-generation bit-rate efficiency solution. aptX HD that enables high definition sound quality that is indistinguishable from ‘hi res’ (24/96) content – again, when transmitted over a Bluetooth connection. This was launched at CES in January this year, and already there are aptX HD enabled products on the market, including the LG G5 handset and LG Tone headset.

Then there’s the latest aptX codec used in the professional industry: aptX Live. aptX Live was designed specifically for digital wireless microphones. It’s a 16-bit, 48kHz mono codec that was brought into play as a result of the migration from analogue to digital television almost a decade ago. It delivers exceptional acoustic performance, low latency and a high resilience to bit errors; features which are fundamental for live performance applications. In the end it was never used by the company that originally commissioned it, but aptX Live is now included in products from Sennheiser, Røde and Audio-Technica.

We’re really pleased with both of these developments, and it feels like we’ve come a long way since the academic days, more than 25 years ago now.

How do you see aptX and the audio ecosystem evolving?

It’s clear that excellent sound quality will remain of paramount importance to everyone, professionals, broadcasters and consumers. If anything, people are becoming ever more discerning about quality now that technology is beginning to meet their expectations.

But in particular, the aptX team is focusing on low latency audio – reducing the transmission delay over Bluetooth even further so that it can be used for gaming and video applications. We have developed a version of aptX with a latency of just 40 milliseconds – lower than any other audio codec.

And aptX Live?

The challenge for the wireless microphone manufacturers is to embrace the characteristics of analogue, digitally. aptX Live lets them do that. We see great longevity in the aptX Live product. Supporting robust sound quality and acoustic integrity for applications within live performance and the arts is right at the heart of where aptX came from.

Pictures: Top: The codec technology is used in studio for voice-over and ADR work and much more besides. Second: Jonny McClintock. Third: Sennheiser Momentum 2 headphones implement aptX. Last: New logo after the Qualcomm takeover.