Page 51

EETE FEB 2014

320DA830 SoC from Texas Instruments used in the example above offers a single device with an ARM core and floating point DSP core, along with a large number of I2S digital audio interfaces to support direct connection to an HDMI transceiver for input and a digital input Class D amplifier ICs for output. The DSP decodes multichannel Dolby and DTS compressed audio formats back to multichannel surround PCM audio. In the early 2,000s five channels were standard; systems with 11 channels are now common and newer emerging formats support virtually unlimited number of audio object channels that are then mapped to as many physical speaker locations as desired. Using a Linux based host processor in the soundbar makes adding wireless features such as Bluetooth and Wi-Fi much easier as the protocol stacks are available either in community supported versions or commercially supported software libraries. Bluetooth includes the SBC codec for stereo audio; when operated at its highest bit rate it offers quality levels near that of typical MP3/AAC downloaded content. Most Bluetooth stereo audio devices will support AAC, but oddly enough there are almost no sources from portable electronic devices for MP3 over Bluetooth, even though that is a dominant download format. The co-existence of multiple RF sources (Bluetooth, Wi-Fi, wireless subwoofer) in a soundbar with high power Class D amplifiers and a lot of digital logic are a serious EMC design issue that must be factored into the industrial design from the beginning. While active soundbars provide much better sound than the TV, they must still be wired to all the audio sources and the TV. Some people prefer the experience of five or seven physical speakers versus the psycho-acoustic methods used for only a soundbar positioned below the TV screen. In both cases physical A T L A N T I C P A C I F I C O C E A N wires present a problem when setting up a system in an existing space. Many soundbars include a wireless link to the subwoofer; being physically large the subwoofer can then be placed in an unobtrusive location and/or located to produce better bass performance. There are multiple vendors offering devices for this purpose (for example TI’s CC8520 PurePath CC8520 Wireless audio IC was used in the system described earlier). The problem is extending that wireless link to multiple speakers for the full surround sound experience, including not having to run wires from all of the sources (cable TV box, game console, etc) to the front sound bar. Different proprietary schemes exist, some use compression to lower the bit rate to simplify the radio requirements but would still not support seven audio channels plus a sub woofer. A new standard for this purpose has been developed by the Wireless Speaker and Audio association (WiSA). The WiSA Compliance Test Specification (CTS) outlines an interoperability Automotive Electronics www.automotive-eetimes.com www.electronics-eetimes.com Analog P A C I F I C O C E A N O C E A N testing and certification program aimed at products that offer multi-channel wireless, interference-free, uncompressed HD quality audio. Operating in a 5 GHz UNII band more RF channels are available to avoid the congestion consumers can experience in 2.4 GHz and 5GHz unlicensed bands. The WiSA technology provides up to 8 channels of 24 bit uncompressed audio at up to 96 kHz sample rates with less than 5 milliseconds latency. These characteristics allow for the highest possible audio quality with no artifacts from compression. Using the WiSA standard for audio transport, an active soundbar could offer the left, center, and right (LCR) front channels, and wirelessly send out the subwoofer, surround, and rear channels for the full 7.1 surround sound experience. Bang and Olufsen, known world wide for unique and high quality systems, introduced complete WiSA-based systems at CES 2014. Your Global Link to the Electronics World A R C T I C O C E A N A T L A N T I C O C E A N AUTOMOTIIVE ANALOG www.analog-eetimes.com engineering europe www.microwave-eetimes.com www.electronics-eetimes.com Electronic Engineering Times Europe February 2014 35


EETE FEB 2014
To see the actual publication please follow the link above