independent of it. Microphones are not always table-mounted; they can be suspended from the ceiling, built into (and coordinated with) a camera or attached to a lapel. They can be wired or wireless. Wireless lavaliere microphones are often preferred, but speakers may forget to remove them before leaving the room. They are also susceptible to RFI (radio frequency interference). A combination of microphones can be used in a single application, as long as they are arranged to avoid feedback. The number of microphones supported by a system (e.g., the number of audio input ports) should be considered. To provide the best coverage, customers often order additional microphones and locate them strategically to maximize coverage. Moreover, when it comes to coverage, microphones should be evaluated in terms of pattern. They can be unidirectional or omnidirectional. Unidirectional microphones are designed to cancel out sound that does not emanate from a certain point. They are ideal for lecture applications but, because of their dead spots, speakers must be aware of where they are positioned in relation to them. Omnidirectional microphones detect sounds from all directions and are preferable for most group applications. Video Communications: The Whole Picture Audio Features The audio-oriented features of video communication systems vary. The most basic include audio-only bridging, or the ability to include those without video communication equipment, and audio out-dialing. Out-dialing is an important feature that should be supplemented through a dialing keypad. An audio call can be used to dial someone on the other end when there are problems with establishing the video component of a conference. If audio dial uses a line from a PBX or switchboard, it is helpful to have a switchhook flash key that can be used to access PBX features such as three-way audio conferencing. A recorder jack is also a useful feature. All systems should include a mute button, which temporarily removes audio from the stream of bits sent to the dista