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Wireless CD-Quality Music Seen With No ‘Perceived’ Interference

Wireless technology from semiconductor designer Avnera promises uncompressed CD-quality music with no perceived interference in home and portable audio applications.

The AvneraAudio technology, promoted as the most “interference-resistant” 2.4GHz technology available, transmits uncompressed music in 48kHz/16-bit PCM form with “no audible or perceived interference,” the company said. The technology already appears in three products, and the number will grow to 15 SKUs during the first quarter of next year, the company said.

Current products incorporating AvneraAudio chips include a $99 universal wireless kit for home theater surround speakers under Best Buy’s Rocketfish brand. The other two products are a pair of $199 Acoustics Research headphones launched during the summer and a Polycom $179 wireless USB Internet phone, due in October, for use with a PC.

The next round of products that will incorporate the AvneraAudio reference design will include PC and MP3 accessories, including an iPod dock, executives said. The technology doesn’t yet distribute 5.1-channel audio.

The 3.5-year-old company contends its 2.4GHz solution is less expensive, easier to set up, more interference-resistant and better sounding than rival 2.4GHz technologies, thus reducing the number of returns that plague other wireless systems. “Best Buy doesn’t sell [HTiB] manufacturers’ wireless rear-speaker kits anymore because of the high return rates, but they started selling ours [using the Rocketfish house brand],” said product development VP Mats Myrberg. For wireless speaker kits, sound quality has been the biggest challenge, he said, but Avnera’s solution was designed from the ground up for audio and music.

To deliver music over the air with as little interference as possible, Avnera combines dynamic frequency selection, intended to ensure a clear channel is always used, with multiple error-correction technologies that don’t cause dropouts and don’t require the use of latency-inducing buffering, which creates lip-syncing problems when video soundtracks are streamed, Myrberg said.

To transmit over one of 40 possible 2MHz-wide channels, an Avnera product scans the spectrum when it is turned on, finds a clear channel and stays on it, said marketing director Monica Enand. “We scan the spectrum all the time, and once it hears interference, it goes to another clear channels already selected in advance, so it always goes to a clear channel.”

Also to prevent interference, Avnera uses two separate antenna systems on both the transmit and receive sides and automatically switches between the two to deliver the best signal.

If interference occurs despite these precautions, Avnera uses forward error correction and other techniques to avoid the dropouts and latency problems created by data-oriented technologies such as Wi-Fi and Bluetooth, which resend data packets that are not received. Resending lost data is “fine for data applications,” the company explained, “but can create interruptions in music as well as noise clicks and pops.” Retransmitting lost data also requires the use of a memory buffer that adds a high amount of latency, creating lip-syncing problems when viewing video, Myrberg added.

In lieu of restransmitting lost data into a buffer, Avnera uses two techniques similar to those used in the Redbook-CD standard to prevent audio-signal dropouts: forward error correction and interpolation, Myrberg said. To prevent distortion resulting from short bursts of interference, forward error correction techniques send redundant data. To overcome longer burst of interference, Avnera conceals the error by filling in, or interpolating, lost data, as does the Redbook CD standard. In addition, Avnera uses time dispersion to spread out errors over time to conceal long burst of interference, Myrberg said.

To reduce the chances of interfering with other 2.4GHz products in a home, Avnera’s solution dynamically raises and lowers power output as the distance between transmitter and receiver changes. Dynamic power output also improves battery efficiency in portable applications.

The range of the current solution is 45 feet through walls, but an additional power chip can extend range to more than 100 feet.