30ft (9 meters)

< 0.03%

2.4-2.4835 GHz

< 20mSec

100 x 30 x 10 mm

20Hz to 22KHz (+/- 1.5 dB)

830 mV

65 dB

The W2 uses uncompressed CD-quality transmission technology with no network setup, software, or computer required. The Wi-Fi-based system we use is an all-digital PCM encoded stream sent over a closed network that includes some really clever error correction and very low latency, which means that your music gets to your stereo fast without any lag, loss in sound quality, or interference from other wireless products or microwave ovens, cordless phones, etc.. The Sender doesn't need to be charged and you have full control over your iPod, with no sluggish menus or lack of volume control as is common with other docks, remotes, and wireless iPod adapters. The key features that make W2 better than most wireless systems currently on the market are the ease of setup, fixed low latency, audio quality, lack of dropouts, and high interference tolerance.

The system used in the W2 was designed and tested to ensure that interference-free audio quality is preserved while sharing the RF spectrum with other common wireless transmission technologies such as WLAN, Bluetooth, microwave ovens, cordless telephones, and others. The system was tested end-to-end system performance using PEAQ, the latest perceptual quality measurement standard, to ensure the best resulting overall design.

Previous attempts at wireless transmission of high-quality audio, including infrared and digital, have suffered from poor reliability - for example interference, dropouts, clicks and pops, static, etc.. Audioengine's solution includes several strategies to overcome these problems. One of these is dynamic channel selection, whereby the 2.4 GHz ISM band is split into 40 narrow subchannels. The wireless Sender (transmitter) and Receiver implement an algorithm to dynamically determine which of those subchannels are currently free and then switch to available subchannels with no loss of audio fidelity. If an interfering device enters the picture, then the system changes channels. When the Sender and Receiver are close to each other, the Sender automatically reduces power to lengthen battery life of your iPod and to reduce possible interference with other devices in the 2.4 GHz band, such as wireless routers. The chips implement two antennas and the antenna with the best signal is chosen dynamically. Should the RF path fail momentarily, the Receiver implements error correction and error hiding to minimize the effects of data loss. In addition, in the transmitted signal individual audio samples are spread in time, so that the effect of a brief data loss is reduced. Although none of these techniques is by itself new, the combination of techniques is new and appropriate for these applications.

The W2 incorporates a real-time streaming transmission technology designed specifically for music. It includes 6 quality protection innovations to achieve the most robust audio link in its category:

Error-tolerant coding that incorporates forward error correction (FEC) coding. FEC ensures that lost bits can be completely reconstructed for common interferers and sources of bit errors. The coding is optimized for lossless performance against common and known interferers. FEC also enables error detection so the system knows when and where data is corrupted. It is analogous to techniques employed on Redbook CDs where the laser head incurs bit-errors as a result of imperfections in the pickup of data from the optical media.

For larger interferers, W2 employs sample interleaving and sample error concealment (SEC). This allows the system to compensate gradually during periods of increasing signal degradation, thus minimizing audible discontinuities. When encountering interference bursts -- up to 6ms in duration -- SEC can recover every alternate sample, after which the hardware DSP performs linear interpolation to recover lost samples.

Packet error concealment (PEC) ensures there are no jump discontinuities in the audio stream during periods of severe interference, giving the system time to find a clean channel.

W2 employs intelligent, Dynamic Frequency Selection. The system avoids interference by constantly monitoring the entire 2.4 GHz spectrum, choosing the channel that can achieve the cleanest transmission. As conditions on a currently occupied channel deteriorate, the system detects this, and switches channels (in under 20ms) without any interruption in the audio stream.

W2 employs dynamic transmit power control. This means that the system is transmitting with only as much power as required to successfully maintain a clear audio connection. This makes W2 coexist better with other 2.4 GHz devices, including WLAN, BT, and other Audioengine wireless devices. W2 combats RF fading, or multi-path-induced signal-strength fluctuations, by natively supporting antenna diversity. Support for dual antennas allows the system to "navigate" around zones of decreased signal strength by creating four possible antenna-to-antenna paths for the system to choose from on a continual basis. The end result is an overall improvement in audio signal robustness due to an improved link margin.

The W2 system divides the band between 2405 MHz and 2477 MHz into 37 discrete, 2 MHz wide channels. Channels numbered 2 through 38 inclusive are used for system operation. The system scans the spectrum and selects two channels that are 18 channels (or 36 mHz) apart and transmits with 50% of the time on one channel (for example channel 2) and 50% on the other channel (for example channel 20). The system stays on these selected channels until the error detection rate reaches a pre-determined level indicating deteriorating RF conditions. The system will select a cleaner channel for transmission and move there without any drop in audio.

Wireless LAN networks are utilized throughout the home and office environment, the bulk operating in the 2.4GHz band. Most WLAN systems divide the spectrum into three channels, operate on a fixed channel and occupy 1/3 of the bandwidth. WLAN routers scan the system will only start transmitting if the spectrum is clear. Therefore systems that aim to share the RF space with WLAN routers need to be able to detect and move away from channels that are used by WLAN routers. In addition, systems with a 100% duty cycle on a WLAN channel will block WLAN permanently. The system used in the W2 was designed to coexist with WLAN and other systems operating in the 2.4GHz environment.

Since the W2 transmits on a channel only 50% of the time, it gives WLAN the opportunity to enter the spectrum. When a new WLAN connection is detected, W2 will select a different channel for transmission. Depending on the signal strength and the channel selection, multiple W2 devices can operate in the vicinity of multiple WLAN networks.