Latest-generation wireless audio products such as iPods, iPhones and wireless surround sound products claim to eliminate the cord while delivering crystal-clear audio. I will take a look at if these products keep their promise to provide perfect-quality audio. Furthermore, I will look at the underlying technologies.
Several products come with wireless already built in while others, specifically streaming audio products, frequently have optional wireless ability. Newest generation iPods and cell phones already come with built-in WiFi and Bluetooth support.
Bluetooth is fairly widespread as a low-cost wireless option. However, Bluetooth does have some limitations. These weaknesses are frequently ignored but will have an impact on high-quality audio applications.
1) Short range
Bluetooth generally just provides a 30 foot range. This is adequate for single-room applications. However, this limitation does not permit multi-room streaming using Bluetooth.
2) Audio compression resulting from limited data rate
Bluetooth reliably supports data transmission rates of around 1 Mbps only which is not enough for uncompressed CD-quality audio. For that reason Bluetooth uses audio compression. Audio compression will degrade the audio quality to some degree. High-quality audio transmission normally does not tolerate this kind of degradation. Therefore Bluetooth is typically not used in high-end audio devices.
3) Audio delay
The audio will experience a delay of a minimum of 10 ms mostly because of the audio compression which is a problem for real-time audio applications but less serious for MP3 players.
4) Lacking multi-headphone support
Bluetooth cannot stream to multiple headphones at the same time. This may be a dilemma in cases where several people like to listen to the same Bluetooth transmitter.
WiFi is one more 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 at the same time. It is convenient for streaming music from a PC because of the high availability but is usually not used in wireless headphone devices because of the relatively high power consumption of WiFi.
Wireless speakers and wireless amplifier products for home theater speakers normally use their own proprietary protocol. Entry-level wireless headphones and speakers typically still use FM transmission which offers low cost but is prone to noise and audio degradation.
Newer wireless audio protocols avoid audio degradation by utilizing digital transmission. These often also have mechanisms including forward error correction to cope with interference from other wireless devices.
Sophisticated wireless amplifier products support uncompressed digital audio streaming to maintain the original audio quality. A number of of these protocols permit streaming to an unlimited number of wireless amplifiers which is practical for whole-house audio distribution.
The audio latency ranges from under 1 ms to up to 20 ms. A small latency is key for wireless surround sound applications. Normally newer generation wireless audio transmitters will work at 2.4 GHz. Some transmitter devices, including Amphony’s line of products, operate at the less crowded 5.8 GHz frequency band.
These wireless amplifiers also differ in regard to amplifier output power, standby power consumption and audio quality. A high-quality audio amplifier is crucial for optimum sound quality. Digital Class-D amplifiers offer high power efficiency of not less than 80%. They also have low standby power, generally less than 5 Watts. This minimizes heat and keeps them cool during operation. Some digital amplifiers, on the other hand, have relatively high harmonic distortion. Choosing a low-distortion amplifier is vital. Good-quality wireless amplifiers have audio distortion of lower than 0.05%.
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