Music Without Cable Clutter? – A Look At Wireless Audio Transmitter Products
Avoiding the large clutter of cables has lead to a variety of wireless audio transmitter products over the years which promise to untie your home audio equipment. Can these products make good on their promise to eliminate the cable clutter? What influence has changing technology had on their performance?
AM and FM radio was launched several decades ago and was the earliest kind of wireless audio transmission. While still being popular today, FM radio is now being substituted by recent technologies including HD radio, satellite radio and DAB broadcasts. Today a multitude of consumer products exist such as wireless microphones, wireless surround sound kits, Bluetooth audio transmitters, baby monitors etc which cut the cord by transmitting audio wirelessly.
One of the main application for wireless audio is distributing music all through the home and installing speakers without running speaker cables which is a big difficulty in homes that are not wired for audio. We will take a look at the advantages and disadvantages of today's wireless audio technologies.
Let’s look at the most traditional technology first: FM broadcasts. FM audio transmitters send the audio by utilizing a high-frequency signal which is constantly changing in frequency according to the audio signal. This technique is known as frequency modulation or FM for short. The biggest advantage of FM transmitters is their simplicity and thus cost as well as range. While the majority of today's 900 MHz products use FM transmission, FM has some major problems.
The first problem is the fact that the transmission will pick up noise and thus there will be some hiss or static. The amount of noise will in fact vary based on the position 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 known as multi-path fading. Some wireless FM transmitters utilize two antennae in an effort to deal with with this phenomenon (diversity receivers). FM radios will easily pick up interference from other consumer devices which is another difficulty.
Bluetooth has gained popularity lately for wireless audio transmission even though this protocol was primarily designed to connect computer peripherals. Bluetooth will convert he audio into a digital format. This data is then sent via the Bluetooth wireless protocol. Bluetooth is fairly robust in terms of interference and is well standardized. Bluetooth, on the other hand, has some pitfalls in regard to wireless audio since it was not designed for wireless audio originally. The first drawback is the limited range which typically would be 30 ft or less. The next drawback is the fact that Bluetooth does not have sufficient space to transmit CD-quality audio and therefore the audio is compressed first. As a result of the audio compression, the audio quality will decrease. Bluetooth will cause a delay or latency to the audio signal which is a problem for surround sound and video applications because the wireless loudspeakers will be out of sync with the remaining loudspeakers and video.
Satellite radio and digital terrestrial radio technologies offer high range but use extensive audio compression leading to deterioration of the audio signal and have an audio delay of several seconds.
Another technology transmits the audio signal without compression digitally. This technology is used in wireless audio transmitters from Amphony. The audio signal will keep CD quality because no audio compression is used. The audio latency of this technology is less than 1 ms. Therefore it can be used for real-time applications such as wireless speaker kits in home theater setups.
This technology is quite robust against radio interference from other wireless transmitters by utilizing a technique known as forward error correction. The Amphony transmitters operate at 5.8 GHz. This frequency space is less crowded than the 900 MHz or 2.4 GHz bands consequently leading to a further improvement of performance. An advantage over Bluetooth is the ability to transmit audio to any number of wireless receivers from a single transmitter. This is important for distributing audio to multiple rooms in the home.