Audio will define the success of the rear-seat entertainment industry
30 June 2011
Thomas Carmody, CSR's head of connectivity marketing for automotive, outlines why the success of rear seat entertainment may all depend on its choice of CODEC. But what factors need to be considered?
It’s pretty clear that the Rear Seat Entertainment in cars is really starting to take off. Evidence of the emerging market for Rear Seat Entertainment (RSE) systems can be seen in the exciting recent announcements of early adopters such as Audi, Renault and PSA*.
These manufacturers, and others, are already seeing fit to offer RSE electronics as options, as well as there being a plethora of aftermarket devices.
The fact that manufacturers are starting to offer RSE as factory installed systems indicates that the market is beginning to assign real worth and commitment to these electronics platforms as genuine value-adds for new cars. Rear Seat Electronics give car manufacturers and OEMs alike a real opportunity to differentiate and innovate. It seems likely that this trend will continue.
According to a recent Market Playground report** GM motors has admitted to eyeing the sector, and iSuppli*** predicted in mid-2010 that the market would almost double by 2015. And as RSE systems proliferate we will increasingly see factory-installed devices appearing in new vehicle models in the high and medium value vehicle segments.
However, there is a potential design related ‘fly in the ointment’ that this market needs to be mindful of: wireless audio quality and latency.
We’ve already seen significant in-roads into the car of infotainment-enabled telematics and navigation devices. Given the increasingly cost-effective nature of silicon that can support DSP-intensive entertainment functions, this will only increase.
However, delivering entertainment to the rear seat presents a slightly different case.
The experience needs to be personal, nondistracting, clear and synchronised. Before all this, however, lowering the clutter of wires and the weight of in-car trunking is a major design consideration for OEMs. Above all else, the system needs to be designed to be wireless.
The intended and likely applications of wireless electronics in rear seat entertainment are fascinating. In the most immediate-term we’re likely to see the development of Bluetooth low energy remote controls and keyboards for rear seat infotainment systems. Early OEM adopters such as Audi, Renault and PSA are already realising these applications. As we look further into the future where in-vehicle Wi-Fi becomes pervasive, the use of Wi-Fi technology as the wireless fat pipe to deliver cloud and media services such as general internet, films, games and audio also becomes important.
However, it is my opinion that one of the lynch-pins of the whole experience is the availability of high-quality, low-latency audio.
In use cases such as these Infrared (IR) and latterly Bluetooth have generally been the favoured means of wireless transmission for audio delivery to stereo headphones. Wi-Fi has proven fine for some streaming applications where power consumption and latency are not such an issue. But Bluetooth, with its lower overheads, can do the same job with much less latency and better power-consumption, which makes it far more appropriate for battery-powered wireless entertainment devices.
Moreover, while decent proprietary wireless audio technology ecosystems may exist, consumers have long-ago voted with their feet for Bluetooth’s standardisation.
This prevents buyers having to sign into limited ecosystems of devices from a limited number of suppliers, often with much less choice and fewer cost options. Bluetooth’s ability to handle multiple users within a particular ecosystem of products has also become important.
Bluetooth is clearly the best option overall for the sector. However, traditionally, Bluetooth has struggled to fulfill one or two key audio-transport requirements of OEMs servicing the automotive industry.
With a specific focus on audio, both synchronised to video and as stand-alone content, decision makers of in-car entertainment solutions have been driven by key metrics on absolute quality. Generally speaking, they look for 16 bit data, with a sampling frequency (Fs) of 44.1 kHz, (or 10 Hz to 20 kHz frequency bandwidth). In other words CD-quality audio.
In order to achieve ‘lip sync’, which is particularly important for games and videos, latency should typically be under 40 milliseconds (ms), which is the rough duration of a single (1/24th) frame of film. It is acknowledged that it would be preferable to bring this figure closer to 30 ms.
For stereo audio, the Bluetooth A2DP profile has long been regarded a good-quality option for audio streaming. This mandates the Sub-band Coding (SBC) CODEC for use within the transport layer.
Unfortunately, however, the majority of implementations of A2DP default to a medium quality option using a Bit Pool of 32.
This results in SBC-encoded audio that was more comparable to FM quality (32 kHz Fs or 10 Hz to 15 kHz frequency bandwidth).
Additionally, SBC’s underlying compression techniques are based on a frame of samples. This, unfortunately, has culminated in a combined Bluetooth and audio CODEC latency of around 100 ms; not ideal for today’s rich multimedia experience.
Because of these perceived restrictions in performance, rather than using Bluetooth, OEM automotive manufacturers have been forced away from standards based options to the more inflexible and constraining solutions offered by proprietary vendors. This is something that really needed to be looked at.
My own company decided to proactively research and evaluate pre-existing alternative CODECs for Bluetooth A2DP that it felt addressed these issues, and which could then be implemented in the automotive space.
The aptX CODEC we selected after rigorous evaluation has been a major player in the professional audio industry for nearly 20 years. It has been adopted by the post-production, cinema, TV and music sectors for both storage and streaming applications, as well as for low-latency transport of broadcast-quality audio from studio to transmitter. In fact, so efficient has aptX proved that it has been mandated by the European Broadcast Union for all Public Service Broadcasters in Europe and affiliate members across the globe. As a result it is implemented in the vast majority of the 44,000 public and commercial radio stations world-wide.
For these applications we found it best to go with a CODEC that achieves its nondestructive compression process through innovative procedures embedded within a wider ADPCM process. Using a gentle 4:1 compression ratio, aptX can deliver CD audio quality that is indistinguishable from the PCM original with a coding latency of only 1.92 ms. We found this to be the only CODEC for Bluetooth A2DP that could achieve the combination of quality and efficiency demanded by the RSE industry.
In terms of audio quality, empirical data indicated an average figure of -0.067 using ITU-R BS-1116-1 test standards for judging the performance of high quality audio CODECs. This method uses a scale from 0 to -5, where -1 is deemed to be imperceptible from the original source content. Where future in-car products may incorporate anything from Blu-ray players to HD Audio music files, the basic message we’d share is that companies need to futureproof their audio offerings.
But as the evolving capabilities of the RSE industry are telling us, latency needs to hammered right down as a priority. The aptX CODEC enjoys a novel sample-based architecture. Due to the 4:1 compression ratio, granularity in terms of editing points can be brought down to four samples. The result of being able to slice the CODEC so thin is that it allows the Bluetooth packets to be populated in a much more efficient manner. This reduces the need for extensive buffering thus further decreasing overall system latency to around 32 ms, while retaining RF robustness.
Once companies providing audio solutions to the RSE industry get past audio issues they can move on to the bigger things. The automotive industry can consider higher-level user requirements such as the connectivity ecosystem, cost in terms of silicon and system, and the all-important intuitive userinterface so often lacking in today’s products.
Furthermore, OEMs need to plough effort into future-proofing the lifecycle of automotive-grade products and assist with the intuitive integration of these devices with other personal networking products like smartphones and tablets.
I too predict this is going to be an exciting few years for automotive rear-seat infotainment
References
*http://www.audi.co.uk/new-cars/a8/a8-l/audio-and-communication/rear-seatentertainment.html
http://www.trgupdate.com/tab4/piece/paris-renault-espace-receives-update-andstandard-rse/
http://www.peugeot.co.uk/vehicles/peugeot-car-range/peugeot-5008/
**http://marketplayground.com/2011/01/20/gm-nysegm-eye%E2%80%99s-netflixnasdaqnflx-in-the-car/
***http://www.isuppli.com/automotive-infotainment-and-telematics/news/pages/car-rear-seat-entertainment-shipments-set-to-nearly-double-by-2015.aspx
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