Wireless audio has become popular. A multitude of consumer products which include wireless headphones are eliminating the cable plus assure greatest freedom of movement. I am about to investigate how newest wireless systems are able to cope with interference from other transmitters and how well they work in a real-world situation.
The popularity of cordless gizmos including wireless headphones has caused a quick increase of transmitters which broadcast in the most popular frequency bands of 900 MHz, 2.4 Gigahertz and 5.8 GHz and therefore cordless interference has become a serious issue.
The most cost effective transmitters normally transmit at 900 MHz. They operate similar to FM stereos. Considering that the FM transmission has a small bandwidth and thereby just uses up a tiny part of the available frequency space, interference can be avoided through changing to a new channel. Today's sound products use digital audio transmission and often work at 2.4 GHz. These digital transmitters transmit a signal that takes up far more frequency space than 900 MHz transmitters and so have a greater potential for colliding with other transmitters.
Simply changing channels, however, is no dependable remedy for steering clear of specific transmitters that use frequency hopping. Frequency hoppers including Bluetooth products as well as several wireless phones are going to hop throughout the whole frequency spectrum. As a consequence transmission over channels will be disrupted for brief bursts of time. Real-time audio has fairly strict requirements concerning stability and low latency. In order to provide those, additional means are needed.
An often utilized method is forward error correction in which the transmitter sends additional information with the audio. Using some advanced algorithms, the receiver is able to fix the information that might in part be damaged by interfering transmitters. Subsequently, these systems can transmit 100% error-free even when there is interference. Transmitters employing FEC can transmit to a great number of cordless receivers and does not need any kind of feedback from the receiver.
In situations where there is only a small number of receivers, often a further method is utilized. The cordless receiver sends data packets to the transmitter to confirm proper receipt of information. The transmitters includes a checksum with each information packet. Every receiver can determine whether a specific packet was received properly or disrupted because of interference. Next, every cordless receiver will be sending an acknowledgement to the transmitter. In cases of dropped packets, the receiver will notify the transmitter and the lost packet is resent. Therefore both the transmitter and receiver need a buffer in order to keep packets. This will create an audio latency, also called delay, to the transmission which is often an issue for real-time protocols like audio. Commonly, the greater the buffer is, the greater the robustness of the transmission. Having said that a big buffer can result in a large latency that may lead to problems with loudspeakers not being synchronized with the movie. Wireless products that use this technique, however, can only broadcast to a limited quantity of cordless receivers. Generally the receivers have to be paired to the transmitter. Since each receiver also requires broadcast functionality, the receivers are more pricey to fabricate and also use up more power.
Often a frequency channel can get occupied by a different transmitter. Ideally the transmitter is going to understand this fact and switch to yet another channel. To do this, a few wireless headphones continuously check which channels are available so that they can instantly switch to a clear channel. This approach is also referred to as adaptive frequency hopping.
The popularity of cordless gizmos including wireless headphones has caused a quick increase of transmitters which broadcast in the most popular frequency bands of 900 MHz, 2.4 Gigahertz and 5.8 GHz and therefore cordless interference has become a serious issue.
The most cost effective transmitters normally transmit at 900 MHz. They operate similar to FM stereos. Considering that the FM transmission has a small bandwidth and thereby just uses up a tiny part of the available frequency space, interference can be avoided through changing to a new channel. Today's sound products use digital audio transmission and often work at 2.4 GHz. These digital transmitters transmit a signal that takes up far more frequency space than 900 MHz transmitters and so have a greater potential for colliding with other transmitters.
Simply changing channels, however, is no dependable remedy for steering clear of specific transmitters that use frequency hopping. Frequency hoppers including Bluetooth products as well as several wireless phones are going to hop throughout the whole frequency spectrum. As a consequence transmission over channels will be disrupted for brief bursts of time. Real-time audio has fairly strict requirements concerning stability and low latency. In order to provide those, additional means are needed.
An often utilized method is forward error correction in which the transmitter sends additional information with the audio. Using some advanced algorithms, the receiver is able to fix the information that might in part be damaged by interfering transmitters. Subsequently, these systems can transmit 100% error-free even when there is interference. Transmitters employing FEC can transmit to a great number of cordless receivers and does not need any kind of feedback from the receiver.
In situations where there is only a small number of receivers, often a further method is utilized. The cordless receiver sends data packets to the transmitter to confirm proper receipt of information. The transmitters includes a checksum with each information packet. Every receiver can determine whether a specific packet was received properly or disrupted because of interference. Next, every cordless receiver will be sending an acknowledgement to the transmitter. In cases of dropped packets, the receiver will notify the transmitter and the lost packet is resent. Therefore both the transmitter and receiver need a buffer in order to keep packets. This will create an audio latency, also called delay, to the transmission which is often an issue for real-time protocols like audio. Commonly, the greater the buffer is, the greater the robustness of the transmission. Having said that a big buffer can result in a large latency that may lead to problems with loudspeakers not being synchronized with the movie. Wireless products that use this technique, however, can only broadcast to a limited quantity of cordless receivers. Generally the receivers have to be paired to the transmitter. Since each receiver also requires broadcast functionality, the receivers are more pricey to fabricate and also use up more power.
Often a frequency channel can get occupied by a different transmitter. Ideally the transmitter is going to understand this fact and switch to yet another channel. To do this, a few wireless headphones continuously check which channels are available so that they can instantly switch to a clear channel. This approach is also referred to 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 regarding wireless headphones from Amphony's website.
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