Beaverton, Ore. — 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 (www.avnera.com).
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.
Although the unlicensed 2.4GHz band is crowded with Wi-Fi and other wireless technologies, Avnera chose to work within the band because “it’s the only globally available band” in the unlicensed ISM (industrial, scientific and medical bands) and suppliers prefer to work with a global standard to keep their SKU counts down, said marketing director Monica Enand.
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 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.” The technology differs from the adaptive frequency hopping spread spectrum (AFHSS) technology used in such products as 2.4GHz cordless phones. That technology, she said, continuously hops through channels in the 2.4GHz band with a predictable hopping pattern. “When it hops into a bad channel, it avoids that channel in the future, but it [the technology] doesn’t work well because it doesn’t stay in a channel long enough to know if there is a problem,” she contended.
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 said.
In lieu of retransmitting 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.
As a result, Avnera’s technology overcomes 6ms interference bursts, which can be caused by turning on a microwave oven, he said.
To send high-quality audio over interference-free channels, Avnera streams uncompressed 48kHz/16-bit PCM over the air instead of compressed music. The stream’s quality exceeds that of Redbook CD’s 44.1kHz/16-bit PCM standard, and it reduces the number of music-file conversions needed to stream music from a PC, Myrberg explained. If a wireless transmitter is connected to a PC’s USB port, for example, a PC converts compressed music files to PCM before sending it to the transmitter. Transmitters using rival wireless technologies would then convert the PCM stream to compressed MP3 or AAC before sending it over the air, Myrberg contended. Avnera would transmit the PCM stream without conversion.
With rival transmitters, there would be even more conversions if the transmitter is connected to a PC’s analog output, Myrberg noted. A PC would convert a compressed file from its hard drive to PCM before converting it to analog for delivery through an analog output, he explained. A rival transmitter would then reconvert the signal to PCM and convert it once again to a compressed format for over-air streaming. An Avnera transmitter, in contrast, would convert the PC’s analog stream only once for over-air transmission in PCM form.
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.
Besides better sound quality, the current generation of Avnera’s design is said to cost suppliers 30 percent less than competing technologies because the company integrated multiple chips onto a single chip. A typical wireless headphone requires eight chips and 131 separate parts, but Avnera got that down to two chips and 65 parts onto a single 1-inch by 1-inch circuit board, which includes the battery charger, said Enand.
