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.
AM and FM radio was introduced several decades ago and was the first type of wireless audio transmission. While still being popular today, FM radio is now being replaced by new technologies including HD radio, satellite radio and DAB broadcasts. A range of today's wireless consumer products cut the cord such as wireless surround sound kits, baby monitors, wireless microphones and Bluetooth transmitters.
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.
FM transmitters are using the most traditional technology in which audio is sent by changing the frequency of a radio-frequency carrier. This technology is called frequency modulation or FM. It is fairly simple to implement. Thus FM transmitters are very cost-effective. Also, FM transmission offers high range. As a result, most of today's 900 MHz wireless headphones use FM transmission. However, FM has some major drawbacks.
The FM signal will pick up static. Therefore there will be noticeable background noise. The amount of static will depend on the location of the transmitter and radio. FM radio waves are often reflected by walls and obstacles. This will cause several components to cancel each other out thus causing a varying signal quality in different locations. This phenomenon is called multipath fading. One method to cope with this problem is using two antennae instead of one. Products using this method are called diversity receivers. FM radios will easily pick up interference from other consumer devices which is another problem.
Another technology which has gained popularity recently is called Bluetooth. Bluetooth was originally designed to connect computer peripheral devices wirelessly. Bluetooth will convert he audio into a digital format. This data is then broadcast via the Bluetooth wireless protocol. While offering high robustness against wireless interference, Bluetooth has several problems in regard to audio transmission since it was never designed with the purpose of transmitting audio. The first drawback is the limited range which typically would be 30 ft or less. The second problem is the fact that Bluetooth does not have enough space to transmit CD-quality audio and therefore the audio is compressed first. This compression will result in a loss of audio quality depending on the degree of compression. Bluetooth will introduce a delay or latency to the audio signal which is a problem for surround sound and video applications because the wireless speakers will be out of sync with the remaining speakers and video.
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.
This technology is fairly robust against radio interference from other wireless transmitters by using a method called forward error correction. Rather than using the crowded 900 MHz and 2.4 GHz frequency bands, Amphony products operate at 5.8 GHz and thus offer high robustness. An advantage over Bluetooth is the ability to send audio to any number of wireless receivers from a single transmitter. This is important for distributing audio to multiple rooms in the home.
AM and FM radio was introduced several decades ago and was the first type of wireless audio transmission. While still being popular today, FM radio is now being replaced by new technologies including HD radio, satellite radio and DAB broadcasts. A range of today's wireless consumer products cut the cord such as wireless surround sound kits, baby monitors, wireless microphones and Bluetooth transmitters.
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.
FM transmitters are using the most traditional technology in which audio is sent by changing the frequency of a radio-frequency carrier. This technology is called frequency modulation or FM. It is fairly simple to implement. Thus FM transmitters are very cost-effective. Also, FM transmission offers high range. As a result, most of today's 900 MHz wireless headphones use FM transmission. However, FM has some major drawbacks.
The FM signal will pick up static. Therefore there will be noticeable background noise. The amount of static will depend on the location of the transmitter and radio. FM radio waves are often reflected by walls and obstacles. This will cause several components to cancel each other out thus causing a varying signal quality in different locations. This phenomenon is called multipath fading. One method to cope with this problem is using two antennae instead of one. Products using this method are called diversity receivers. FM radios will easily pick up interference from other consumer devices which is another problem.
Another technology which has gained popularity recently is called Bluetooth. Bluetooth was originally designed to connect computer peripheral devices wirelessly. Bluetooth will convert he audio into a digital format. This data is then broadcast via the Bluetooth wireless protocol. While offering high robustness against wireless interference, Bluetooth has several problems in regard to audio transmission since it was never designed with the purpose of transmitting audio. The first drawback is the limited range which typically would be 30 ft or less. The second problem is the fact that Bluetooth does not have enough space to transmit CD-quality audio and therefore the audio is compressed first. This compression will result in a loss of audio quality depending on the degree of compression. Bluetooth will introduce a delay or latency to the audio signal which is a problem for surround sound and video applications because the wireless speakers will be out of sync with the remaining speakers and video.
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.
This technology is fairly robust against radio interference from other wireless transmitters by using a method called forward error correction. Rather than using the crowded 900 MHz and 2.4 GHz frequency bands, Amphony products operate at 5.8 GHz and thus offer high robustness. An advantage over Bluetooth is the ability to send audio to any number of wireless receivers from a single transmitter. This is important for distributing audio to multiple rooms in the home.
About the Author:
Gunter Fellbaum has been developing audio and electronic products for over 10 years. You can get further information about wireless surround sound kits as well as other wireless audio products from Amphony's website.
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