A significant challenge for engineers designing a wireless microphone system is addressing multipath interference. The Audio Ltd A10 digital wireless microphone system devotes significant signal processing resources to achieving robust performance in the presence of both short range and long range multipath. This note briefly explains what multipath is, why it is a problem, and some of the techniques used to mitigate it.
The A10 Digital Wireless System has a significant advantage over analogue FM wireless and other digital wireless systems in its ability to reject interference. This arises because of three main reasons.
Wireless microphone systems are essential tools for production sound. The expectation that every actor on a set or production have their own microphone means that more wireless systems are in simultaneous use than ever, and in increasingly complex setups. While Audio Limited wireless systems such as the En2 and 2040 are great performers, and highly regarded by the professional audio community, the ever-changing landscape of spectrum allocation and regulation means that their FM analogue technology is starting to be a limitation.
Analogue FM wireless system use a compandor circuit in the signal chain to maintain dynamic range. A compander first compresses audio at the transmitter by a fixed compression ratio before RF modulation. At the receiver the signal is then expanded by the same ratio after demodulation. Companders help overcome the noise limits inherent in narrow bandwidth FM radio signals.
The UHF spectrum between 470 MHz and 800 MHz is particularly valuable for wireless microphone systems. This UHF range offers technical properties which allow portable systems to operate with a good balance of required RF output power, RF propagation (good both indoors and out), and small antennae size. Wireless microphone systems operating in the 470 MHz to 800 MHz spectrum share it with over-the-air television broadcasters. Wireless microphones operate in unused frequency spaces between broadcasting television stations and specific licensed bands authorised for wireless microphone use in certain regions of the world.