by Gunter Fellbaum
Eliminating the big clutter of cables has lead to a variety of wireless audio transmitter products over the years which promise to untie your home audio equipment. We will take a look at recent products to see whether they can deliver on their promise to eliminate the cable clutter and we'll examine how changing technology has impacted performance of these products.
Wireless transmission of music has started with the launch of commercial radio broadcasts several decades ago. FM radio is still popular until today although some newer technologies such as satellite radio and digital radio formats such as HD radio and DAB radio have begun to replace traditional FM radio. Today a multitude of consumer devices exist such as wireless microphones, wireless surround sound kits, Bluetooth audio transmitters, baby monitors etc which eliminate the cord by transmitting audio wireless.
One of the main application for wireless audio is to distribute music throughout the home and setting up speakers without running speaker cables which is a big problem in homes that are not wired for audio. Not every technology is perfect when it comes to wireless audio as we will find out.
One of the most traditional technologies is FM broadcasting. Audio is sent via a radio-frequency signal which is modulated (changed in frequency) with an audio signal. This method is called frequency modulation or FM for short. The biggest advantage of FM transmitters is their simplicity and thus cost and range. While most of today's 900 MHz products use FM transmission, FM has some major problems.
The first is the fact that the transmission will pick up noise and thus there will be some hiss or static. The amount of noise will actually vary depending on the location of the radio or receiver. This is due to the fact that the radio signal is bouncing off walls and will cancel itself out at different locations. This phenomenon is called multi-path fading. Using two antennae is one method some devices cope with this problem (diversity receivers). Another problem is that FM radios easily pick up interference from competing wireless transmitters.
Bluetooth has gained popularity recently for wireless audio transmission even though this protocol was primarily designed to connect computer peripherals. Bluetooth audio transmitters will convert the audio signal to digital information and then transmit via the Bluetooth protocol. Bluetooth is fairly robust in terms of interference in is well standardized. Bluetooth, however, has some problems in regard to wireless audio since it was not designed for wireless audio originally. The range of the transmission is only 30 ft or less. Also, Bluetooth does not have enough space to send an uncompressed CD-quality audio signal. Therefore the audio is compressed prior to the transmission. As a result of the audio compression, the audio quality will decrease. The final problem is the fact that Bluetooth will introduce a delay in the signal (also called latency) which is a problem when used together with video since the audio will be out of sync or if used in a surround sound setup where some of the speakers would be out of sync with the hard-wired speakers.
Satellite radio and digital terrestrial radio technologies offer high range but use extensive audio compression leading to degradation of the audio signal and have an audio delay of several seconds.
Another technology which is used in wireless audio transmitters from Amphony send the audio digitally without using audio compression. The signal will retain the original quality by avoiding audio compression. The audio latency of these products is less than 1 ms and therefore this technology is also used in wireless speaker kits for home theater setups.
To be robust against interference from other wireless devices, this technology uses forward error correction. This mechanism can repair errors during the transmission. Amphony products use the 5.8 GHz frequency band which is less crowded than the 900 MHz and 2.4 GHz bands. The result is high reliability. Other than Bluetooth, this technology can operate and number of receivers per transmitter which is key for sending audio to several locations throughout the house.
Gunter Fellbaum has been developing audio and electronic products for over a decade. You can get additional information concerning <a href="http://www.amphony.com/products/wireless-surround-sound.htm">wireless surround</a> sound kits and other <a href="http://www.amphony.com">wireless audio</a> products from Amphony's website.
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