An ever increasing number of cordless products like wireless headphones causes growing competition for the valuable frequency space. I'm going to have a look at a number of systems which are utilized by today's electronic audio systems to determine how well these systems can operate in a real-world situation.
The most common frequency bands which are employed by wireless devices are the 900 MHz, 2.4 GHz and 5.8 GHz frequency band. Mainly the 900 MHz as well as 2.4 GHz frequency bands have begun to become clogged by the ever increasing number of gizmos such as wireless headphones, cordless telephones and so on.
The most cost effective transmitters normally broadcast at 900 MHz. They work similar to FM stereos. Since the FM signal has a small bandwidth and therefore just consumes a small fraction of the available frequency space, interference can be avoided simply by changing to an alternative channel. Modern-day sound systems employ digital sound transmission and in most cases work at 2.4 GHz. These digital transmitters transmit a signal that takes up much more frequency space than 900 MHz transmitters and so have a greater potential for colliding with other transmitters.
A few cordless systems for instance Bluetooth systems as well as wireless phones use frequency hopping. As a result just switching the channel won't avoid these types of frequency hoppers. For this reason modern sound transmitters use specific mechanisms to cope with interfering transmitters in order to ensure continuous interruption-free sound transmission.
One of these strategies is referred to as forward error correction or FEC for short. The transmitter is going to transmit additional information besides the sound data. The receiver utilizes a formula that makes use of the extra data. When the signal is corrupted during the transmission because of interference, the receiver can easily remove the incorrect data and recover the original signal. This technique will work if the amount of interference doesn't rise above a certain limit. Transmitters making use of FEC can transmit to a huge amount of cordless devices and doesn't require any feedback from the receiver.
An additional method utilizes receivers that transmit data packets to the transmitter. The transmitters contains a checksum with each information packet. Every receiver can easily detect whether a certain packet has been received correctly or disrupted as a result of interference. Then, each wireless receiver will be sending an acknowledgement to the transmitter. Given that lost packets must be resent, the transmitter and receivers have to store data packets in a buffer. This kind of buffer causes an audio delay which is dependent upon the buffer size with a bigger buffer increasing the robustness of the transmission. A large latency can be a problem for several applications nonetheless. Especially if video is present, the audio tracks must be in sync with the movie. Additionally, in surround sound applications where some speakers are wireless, the wireless speakers ought to be in sync with the corded speakers. One constraint is that systems in which the receiver communicates with the transmitter usually can only broadcast to a small number of wireless receivers. Furthermore, receivers must incorporate a transmitter and generally consume more current
Often a frequency channel can get occupied by a different transmitter. Ideally the transmitter will realize this fact and switch to another channel. To do so, a number of wireless headphones continually monitor which channels are available to enable them to instantly change to a clear channel. This method is also known as adaptive frequency hopping.
The most common frequency bands which are employed by wireless devices are the 900 MHz, 2.4 GHz and 5.8 GHz frequency band. Mainly the 900 MHz as well as 2.4 GHz frequency bands have begun to become clogged by the ever increasing number of gizmos such as wireless headphones, cordless telephones and so on.
The most cost effective transmitters normally broadcast at 900 MHz. They work similar to FM stereos. Since the FM signal has a small bandwidth and therefore just consumes a small fraction of the available frequency space, interference can be avoided simply by changing to an alternative channel. Modern-day sound systems employ digital sound transmission and in most cases work at 2.4 GHz. These digital transmitters transmit a signal that takes up much more frequency space than 900 MHz transmitters and so have a greater potential for colliding with other transmitters.
A few cordless systems for instance Bluetooth systems as well as wireless phones use frequency hopping. As a result just switching the channel won't avoid these types of frequency hoppers. For this reason modern sound transmitters use specific mechanisms to cope with interfering transmitters in order to ensure continuous interruption-free sound transmission.
One of these strategies is referred to as forward error correction or FEC for short. The transmitter is going to transmit additional information besides the sound data. The receiver utilizes a formula that makes use of the extra data. When the signal is corrupted during the transmission because of interference, the receiver can easily remove the incorrect data and recover the original signal. This technique will work if the amount of interference doesn't rise above a certain limit. Transmitters making use of FEC can transmit to a huge amount of cordless devices and doesn't require any feedback from the receiver.
An additional method utilizes receivers that transmit data packets to the transmitter. The transmitters contains a checksum with each information packet. Every receiver can easily detect whether a certain packet has been received correctly or disrupted as a result of interference. Then, each wireless receiver will be sending an acknowledgement to the transmitter. Given that lost packets must be resent, the transmitter and receivers have to store data packets in a buffer. This kind of buffer causes an audio delay which is dependent upon the buffer size with a bigger buffer increasing the robustness of the transmission. A large latency can be a problem for several applications nonetheless. Especially if video is present, the audio tracks must be in sync with the movie. Additionally, in surround sound applications where some speakers are wireless, the wireless speakers ought to be in sync with the corded speakers. One constraint is that systems in which the receiver communicates with the transmitter usually can only broadcast to a small number of wireless receivers. Furthermore, receivers must incorporate a transmitter and generally consume more current
Often a frequency channel can get occupied by a different transmitter. Ideally the transmitter will realize this fact and switch to another channel. To do so, a number of wireless headphones continually monitor which channels are available to enable them to instantly change to a clear channel. This method is also known as adaptive frequency hopping.
About the Author:
Gunter Fellbaum has been developing audio and electronic products for over a decade. You can get additional details about wireless headphones from Amphony's website.
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