A Peek At Some Of The Coolest Wireless Toys
Recently a great number of wireless audio devices have appeared such as latest-generation wireless headphones, iPods, cell phones and wireless amplifier products that promise to cut the cord. I will examine whether these products keep their claim to deliver perfect-quality audio. Moreover, I will look at the underlying technologies.
Products can be categorized into devices with built-in and those with optional wireless ability. Streaming audio products will often have a plug-in slot for adding a wireless LAN card. Most recent touch-screen iPods and iPhones already have WiFi and Bluetooth built in.
Bluetooth is a fairly low-cost option but has some limitations which are regularly overlooked.
1) Limited range
Bluetooth devices typically only have a 30-foot range which limits Bluetooth to single-room applications.
2) Small data rate – audio compression
Bluetooth will utilize audio compression since it does not reliably offer a high-enough data rate for uncompressed audio. Audio compression will deteriorate the audio quality to some degree. High-quality audio transmission normally does not tolerate this type of degradation. As a result Bluetooth is normally not used in high-end audio products.
3) Signal latency
Due to audio compression, Bluetooth will introduce a signal delay of not less than 10 ms which will cause the audio to be to some extent out of sync in case of video and real-time applications. This is again less of a problem for MP3 players.
4) Lacking multi-headphone support
Bluetooth does not support any quantity of headphones which may be a problem if you have a larger number of people who want to listen to headphones from a single transmitter device.
WiFi is an additional commonly used wireless protocol that is also suitable for audio streaming. WiFi does support uncompressed audio but will have problems broadcasting to a high number of wireless receivers simultaneously. As a result of the high availability, WiFi is suitable for streaming audio from a PC. However, WiFi products have relatively high power consumption. Because of this wireless headphones generally do not use this technology.
Wireless speakers and wireless amplifier products for home theater speakers typically employ their own proprietary protocol. Entry-level wireless headphones and speakers typically still utilize FM transmission which offers low cost but is prone to noise and audio distortion.
More recent wireless audio protocols are based on digital transmission. This prevents audio degradation. Several protocols also incorporate error correction to cope with interference from other wireless products.
Latest-generation wireless amplifiers utilize uncompressed audio transmission. Latest protocols also permit streaming to an unlimited number of receivers. This enables whole-house audio distribution.
The audio latency of these wireless amplifiers is typically between 1 ms and 20 ms. A small-latency amplifier is important for home theater audio. This ensures that all speakers will be in sync. These wireless audio transmitters generally work at 2.4 GHz. There are also some products including Amphony’s line of wireless audio devices that work at 5.8 GHz. Products that work at 5.8 GHz have less competition from other wireless products than those utilizing the crowded 2.4 GHz frequency band.
Wireless amplifiers offer different levels of audio quality, output power and standby power. Digital Class-D amplifiers offer high power efficiency of a minimum of 80%. They also have low standby power, typically less than 5 Watts. This minimizes heat and keeps them cool during operation. Some digital amplifiers, however, have relatively high harmonic distortion. Picking a low-distortion amplifier is crucial. Good-quality wireless amplifiers have audio distortion of less than 0.05%.
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