Feb 12, 2014

An In-Depth Examination Of Today's Wireless Speaker Products

By Mike Heller


An ever growing amount of cordless gadgets which include wireless speakers produces growing competition for the precious frequency space. I will evaluate several systems that are employed by modern electronic audio systems to determine how well these solutions can work in a real-world environment. The rising popularity of wireless consumer gadgets such as wireless speakers has started to cause difficulties with numerous gadgets competing for the restricted frequency space. Wireless networks, wireless phones , Bluetooth and various other products are eating up the precious frequency space at 900 MHz and 2.4 GHz. Wireless sound systems ought to guarantee robust real-time transmission in an environment which has a large amount of interference.

Common FM transmitters typically operate at 900 MHz and do not possess any particular method of coping with interference however switching the transmit channel can be a solution to deal with interfering transmitters. Digital sound transmission is normally employed by more modern audio gadgets. Digital transmitters commonly operate at 2.4 GHz or 5.8 GHz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high.

The most cost effective transmitters typically transmit at 900 MHz. They work similar to FM radios. Considering that the FM signal uses a small bandwidth and thus just uses up a small fraction of the available frequency space, interference can be avoided simply by changing to a new channel. The 2.4 Gigahertz and 5.8 Gigahertz frequency bands are used by digital transmitters and also are getting to be very crowded recently because digital signals take up more bandwidth compared to analogue transmitters.

A frequently employed strategy is forward error correction in which the transmitter sends extra data along with the audio. Making use of several advanced calculations, the receiver can then restore the information that might partly be corrupted by interfering transmitters. Subsequently, these systems can broadcast 100% error-free even when there's interference. Transmitters using FEC on its own generally can transmit to any amount of cordless receivers. This mechanism is normally used for systems where the receiver is unable to resend data to the transmitter or where the quantity of receivers is fairly big, just like digital radios, satellite receivers and so forth.

One of these methods is called forward error correction or FEC for short. The transmitter will transmit additional data besides the sound data. The receiver uses a formula that utilizes the additional data. If the signal is damaged during the transmission as a result of interference, the receiver can remove the incorrect data and recover the original signal. This method works if the amount of interference doesn't go above a certain threshold. FEC is unidirectional. The receiver doesn't send back any information to the transmitter. Thus it is often used for equipment including radio receivers in which the number of receivers is large. A different method uses receivers that transmit data packets back to the transmitter. The transmitters has a checksum with every information packet. Each receiver may determine whether a particular packet has been acquired correctly or disrupted because of interference. Subsequently, each cordless receiver will be sending an acknowledgement to the transmitter. If a packet was corrupted, the receiver is going to notify the transmitter and request retransmission of the packet. Consequently, the transmitter has to store a certain amount of packets in a buffer. Equally, the receiver will have to have a data buffer. This will create an audio latency, also referred to as delay, to the transmission that could be an issue for real-time protocols like audio. Typically, the bigger the buffer is, the larger the robustness of the transmission. A large latency can be a problem for several applications nonetheless. In particular when video is present, the audio tracks should be synchronized with the movie. Additionally, in surround applications in which a number of speakers are wireless, the cordless loudspeakers should be synchronized with the corded loudspeakers. Systems which incorporate this particular procedure, nevertheless, are restricted to transmitting to a few receivers and the receivers consume more energy.

Often a frequency channel can become occupied by another transmitter. Ideally the transmitter is going to recognize this fact and change to a different channel. To do this, some wireless speakers continuously monitor which channels are available so that they can instantly switch to a clear channel. The clean channel is picked from a list of channels which has been determined to be clear. A technique which makes use of this kind of transmission protocol is known as adaptive frequency hopping spread spectrum or AFHSS




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