A large number of wireless audio transmitter products have emerged over the years. They promise to cut the cord to your audio equipment. We will examine the impact of new technologies on the performance of these products. Also, we’ll examine if they keep their promise of eliminating the cable clutter.
The first form of wireless audio transmission was in the form of AM and FM radio stations. 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.
Setting up speakers in another room and distributing music throughout the house are some of the applications of wireless audio. Many homes are not wired for audio. The technologies used today all have pros and cons as we will examine.
FM transmitters are using the most traditional technology in which audio is sent by changing the frequency of a radio-frequency carrier. The technology, which is called frequency modulation (FM), is fairly simple and cost-effecive to build and offers high range. While most of today’s 900 MHz products use FM transmission, FM has some major problems.
FM transmissions will pick up static which is noticeable as a background hiss depending on the location of the wireless receiver. The reason for the varying quality is a phenomenon called multipath fading which is a result of reflected radio waves cancelling each other out. 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.
Another technology which has gained popularity recently is called Bluetooth. Bluetooth was originally designed to connect computer peripheral devices wirelessly. Before the signal is broadcast, Bluetooth transmitters will convert the audio into a digital format. One of the advantages is the high robustness against wireless interference. However, Bluetooth was not designed for audio transmissions. Therefore is does have several problems. Bluetooth only offers a range of 30 ft or less and will compress the audio since it does not offer enough space to transmit an uncompressed CD-quality signal. Due to the compression, the audio quality will be degraded compared to the original. Another problem is that Bluetooth will introduce a delay or latency to the signal during the transmission. This delay is a particular problem for video and surround sound applications. In these applications the sound from the wireless speakers would be out of sync with the video and remaining speakers.
The technologies used for satellite radio and terrestrial digital radio offer high range. However, they also use extensive audio compression. Further, a delay of up to several seconds is introduced.
Another technology sends the audio digitally without bluetooth audio module using audio compression. The signal will retain the original quality by avoiding audio compression. This technology offers an audio latency of less than 1 ms. Therefore these transmitters can be used for wireless speaker kits in a home theater setup and other real-time applications.
To be robust against interference from other wireless devices, this technology uses forward error correction. This mechanism can repair errors during the transmission. Some recent 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.