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Achieve high-quality wireless audio in the car

18 Apr 2013  | Jonny McClintock

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aptX has been used by many brands that rely on high-quality audio including Sennheiser, Samsung, BBC, IRT (representing the regional German broadcasters), SR in Sweden, NHK in Japan, KBS in Korea, Pixar and Disney. The aptX codec has also been widely adopted in the handset market by manufacturers including Samsung, HTC, Motorola and Sharp.

In terms of the latter empirical data has indicated that aptX offers an average figure of -0.067 using ITU-R BS-1116-1 test standards for judging the performance of high quality audio codec's. The scale goes from 0 to -5, where -1 is deemed to be imperceptible from the original source content. Multiple tracks are listened to and scored by a panel of 30 trained acousticians and details on the sum and average are collected.

As previously stated, the aptX codec has a compression/decompression time of 1.92ms. However, the more important feature is the sample based nature of the codec. As the codec has a 4:1 compression ratio, granularity in terms of editing points can be down to four samples.

The result of being able to slice the codec so thin is that the Bluetooth packets can be populated in an extremely efficient manner. This efficiency then allows the buffers to be reduced to a level that overall latency (both codec and Bluetooth transport) can be 32ms, while retaining RF robustness.

A figure of less than 40ms is required for true audio synchronisation or "lip sync," which is a function of the size of the video frame. For any OEM planning on using Bluetooth as part of their rear-seat entertainment solution, making sure they have a solution that contends with SBC latencies and provides true "lip sync" for watching video content or gaming on the rear-seat screen is vital to ensure the best customer experience.

What's next for the automotive industry?
At the beginning of this article, it was outlined that due to the restrictive nature of SBC in Bluetooth, the automotive industry was forced into other proprietary options. However, now that CSR has addressed these frailties, the industry will need to heavily consider connectivity in terms of the ecosystem, ease of use, cost (in terms of silicon and system) and how to future-proof their offering.

Bluetooth is a standard that has been readily adopted by a myriad of consumer electronics manufacturers. Over three billion Bluetooth chips have been sold in the past 10 years. All smartphones and the majority of feature phones and portable media players include Bluetooth as a feature and offer the A2DP profile for wideband stereo audio. The ability for a user who has stored audio on a handset to readily move from home to car to office while streaming audio to headsets and speakers without the need for dongles is truly a compelling vision.

Other proprietary solutions limit the flexibility an OEM can offer to allow users to consume media in the way that they want to, because they are incompatible with other widely-adopted standards including Wi-Fi and Bluetooth. By using these standards a car manufacturer can have rear-seat screens which use Wi-Fi to deliver content from the head end to the screens and Bluetooth to deliver the audio; but they can also support video and audio streaming from a brought in device, for example a smartphone or Portable Media Player, because they use the same standards.

In terms of future-proofing, Bluetooth has a well-defined roadmap as it is managed by the Special Interest Group (SIG) with options for faster data rates and significantly lower power requirements and can address many different use cases and applications outside audio.


CSR has addressed the problems associated with Bluetooth for all applications which require CD-quality audio and low latency by implementing aptX. Kleer developed a proprietary, one-off solution to fill the vacuum that arose before Bluetooth got its house in order. Automotive OEMs now have access to a standards-based solution, which offers wide-scale adoption, ease of use, enjoys pricing associated with economy of scale and features that have been developed by power houses investing in R&D.

About the author
Jonny McClintock is a graduate of Electronics from the University of Ulster and has over 25 years of experience in the audio industry. He was Director of Sales and Marketing for Audio Processing Technology and then for APT Licensing Ltd, before the latter was acquired by CSR in July 2010. He is now Director of aptX Sales and Marketing for CSR.

To download the PDF version of this article, click here.

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