As Jonny McClintock, Director of aptX Sales and Marketing, Qualcomm aptX explains, Bluetooth is widely used as a wireless connection for audio applications including phones, media players and wearables, removing the need for cables. The combination of the AD2P protocol and frame-based codecs used in many Bluetooth stereo audio implementations has led to excessive latency and acoustic performance significantly below CD quality.
This article looks at how Bluetooth audio connectivity has evolved, and whether developers can confidently think beyond wires for audio applications.
According to Ofcom, consumers spend around 1,204 hours a year listening to music on their smartphones, and they expect their devices to deliver good quality audio experiences. Poor acoustic performance, latency and compromised battery life are no longer acceptable. The chief culprit in these limiting factors was the SBC codec as many handset manufacturers first used its lower ‘Bit Pool’ value which reduced every device down to this sub-optimal audio performance. As a result Bluetooth simply could not be used for real time, high quality (i.e. CD quality) applications, and could not offer a realistic replacement for wired connectivity.
What the industry needed was an alternative codec that is able to deliver a consistent ‘CD-like’ audio quality and is widely supported in high performance audio equipment including headphones, automotive audio and home entertainment systems.
The aptX codec, which is based on a 16 bit, ADPCM, 4 sub-band, bit rate reduction sample-based design principles, is able to deliver a consistent ‘CD-like’ audio quality and provides a 40ms system latency which ensures a significantly better consumer experience over Bluetooth. The codec works on a fixed compression ratio algorithm so each aptX implementation guarantees the same audio quality.
The aptX codec does not use any frame format and therefore works efficiently with the A2DP packetised structure. This 16-bit aptX codec was introduced to Bluetooth to address the frailties of SBC and its success was achieved by a set 4:1 compression ratio (ensuring no variability in audio performance when combining source and sink devices from different manufacturers), and an interoperability programme that tests the acoustic integrity, RF robustness and connection and pairing process, of every product that offers aptX.
To augment the audio experience and keep pace with the video industry which moved into high definition video content, the audio industry is now delivering ‘better than CD-quality’ audio.
While the concept of high-res audio is not necessarily new, generally only audiophiles have been asking for it. Today, codecs such as aptX HD, offer 24-bit word depth and 48kHz sampling frequency, and device manufacturers are cottoning on to market demand for it. Manufacturers such as LG have adopted aptX HD in its latest G5 handset as well as the LG TONE Platinum (HBS-1100) headset, providing mobile users with a captivating audio experience wirelessly over Bluetooth.
Beyond handsets, perhaps the next battleground for developers and manufacturers is the car. The automotive industry already invests heavily in R&D to provide good internal acoustics, and look at things like directional shaping, speaker position and quality, wattage and noise isolation to bring this about. Couple this with the amount of time consumers spend in cars and the prevalence of Bluetooth in them, it’s vital the industry ensures Bluetooth delivers the best possible listening and connectivity experience in this environment.
To summarise, by using Bluetooth connected devices with aptX codecs and the latest energy conscious platforms, users can benefit from superior audio quality without the constraints of a wired connection. However, for wireless listening to be ubiquitous, manufacturers need to address other considerations beyond the audio quality of the connection. These include ease-of-use, cost and design of the devices themselves.