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RF/Microwave??

HD audio nixes interference, maintains power budget

Posted: 24 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:HD audio? power budget? signal interference?

In the crowded 2.4GHz wireless band where everything from Wi-Fi to Bluetooth to cordless phones and microwave ovens operates, high-definition (HD) audio communications strategies have to be nimble to avoid interference. By combining very small packet sizes with an adaptive frequency allocation algorithm, STS Inc., a Dutch fabless chipmaker, claims to have nixed interference while maintaining HD audio within a power budget that maintains long battery life for portable devices!albeit with proprietary protocols that are incompatible with other manufacturers' devices.

"The 2.4GHz band has become very crowded, and companies like STS, with proprietary wireless audio solutions, have to position themselves as offering better quality than Bluetooth," said Gartner wireless analyst Stan Bruederle. "The fact is, if you don't need ultrahigh-quality!if you're not doing critical listening in a quiet room!then Bluetooth offers an interoperable solution that will be satisfactory for most listeners."

In order to achieve HD quality in its audio connection, STS touts a proprietary wireless connection algorithm that employs a sophisticated adaptive frequency selection algorithm which it claims virtually guarantees continuous HD audio even when packets become corrupted by interference.

"We have a wideband solution that uses very small packets that can fit in between Wi-Fi and Bluetooth packets, and even microwave ovens turning on, by quickly changing frequencies. We are like the crazy guys in Italy on the scooters that go around and in between the other traffic," said Hans van Leeuwen, chief technology officer at STS. "Our chips continuously scan around to discover where other Wi-Fi, Bluetooth, cordless phones and microwave ovens are operating, then quickly shift frequencies to avoid interference. We do not use a frequency-hopping algorithm like Bluetooth, but a truly adaptive algorithm."

STS introduced its first wireless audio chip!a three-channel device!in 2000 and is entering its fourth generation today with the debut of its latest technology, backward-compatible with previous generations. The 4G technology uses eight separate channels to enable up to four simultaneous channels of bidirectional radio communications among devices, and includes an integral headphone amplifier. STS will show its new generation of wireless audio technology for the first time at the Consumer Electronics Show in Las Vegas, Jan 7-10, 2008.

"Our customers can use the four independent bidirectional channels for separate devices in homewide audio communications, or they can use them all in one room, for instance, to enable wireless surround sound speaker systems," said van Leeuwen.

Retransmission
Unlike competitors such as Avnera Corp., which depends on sophisticated forward error correction techniques, STS uses the same kind of packet retransmission protocols used by data networks such as Zigbee.

"I am a radio engineer whose background is in Zigbee," said van Leeuwen. "Our chips are not using Zigbee, but like Zigbee, our interface robustness comes from retransmission, instead of relying on forward error correction."

As a result, STS claims higher-quality specifications than most standard interoperable solutions. For instance, its HD audio is uncompressed using 24bit, 96KSps and latency is 17ms. This better-than-CD audio quality is thus guaranteed to be synced with the video in home theaters, since the human brain cannot distinguish latency less than 20ms. In addition, the STS chips consume only 25mA, including the built-in headphone amplifier!albeit the chip does not include a radio, which must be provided by the original equipment manufacturer on a separate chip.

STS chips have a 150ft range indoors through walls and 500ft outside for wireless headphones. The company also claims "good as a wire" synchronization among its eight radio channels!100ns.

At CES, STS customer Sony will be showing its latest surround-sound headphones, which use STS' four bidirectional channels to supply Dolby 7.1 HD audio.

- R. Colin Johnson
EE Times




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