The AW2 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 AW2 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 AW2 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 AW2 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, AW2 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.
- AW2 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.
- AW2 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 AW2 coexist better with other 2.4 GHz devices, including WLAN, BT, and other Audioengine wireless devices.
- AW2 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 endresult is an overall improvement in audio signal robustness due to an improved link margin.