High quality wireless audio in the car: how developments in Bluetooth are making it possible

November 01, 2012 // By Jonny McClintock
As the home environment marches towards the reality of wireless connectivity, car drivers and passengers are expecting the same functionality and freedom associated with a wire-free environment. There are two applications where consumers expect to enjoy high-quality audio. The first is streaming content from their smart devices to the head unit and the second is listening to high quality audio from their rear-seat entertainment system while watching a movie or playing a game. Bluetooth, the most ubiquitous of wireless protocols, has the ability to address both these applications but only recently has had the potential to make this possible.

Traditionally Bluetooth as a audio content transport mechanism has struggled to fulfil all the key requirements for automotive OEM'S. With a specific focus on synchronized audio to video and as wideband stereo content, decision makers on in-vehicle infotainment solutions were driven by certain performance metrics. The 2 key requirements being:

  • 16 bit word resolution with a sampling frequency of 44.1 kHz i.e. CD quality (or 10Hz to 20kHz frequency bandwidth)
  • Latency performance of under 40 milliseconds and preferably close to 30 milliseconds.

For stereo audio, the A2DP profile mandated codec of SBC was used within the Bluetooth transport layer. Unfortunately, at its most popularly used implementation (Bit Pool 32), SBC was only able to reproduce audio quality closer to FM quality (32kHz Fs or 10Hz to 15kHz frequency bandwidth). SBC’s underlying compression techniques being Frame Based has culminated in an overall Bluetooth and audio codec latency in excess of 100ms. In addition, SBC could only offer a highly variable latency which removed the option of delaying the video signal, making syncing video and audio for playing games or watching films impossible.

Because of these unattractive features, rather than using Bluetooth, automotive manufacturers were forced away from standards-based options to the more inflexible and constraining solutions offered by proprietary vendors such as SCMS’s Kleer. However, as A2DP is set to stay with us for many years OEMs need to think about dealing with current audio-quality issues, rather than looking for alternative solutions.

As well as this consumers are changing their habits away from AM and FM radio and CDs and are looking to their smartphones as a hub for music and content to be bought in to the car. As a result of this new demand for smartphone integration new car audio designs are increasingly replacing the CD and offering Bluetooth wireless audio connectivity instead. Smartphones can stream content, including music, podcasts and audiobooks, as well as using the cloud to

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