AV Technology - August 2008 - (Page 25)

I n any AV application where there’s more than one microphone in a conference room, auditorium, training center, classroom, or house of worship, chances are there’s an automatic microphone mixer somewhere behind the scenes — or at least, there should be. Today’s automatic microphone mixers have so many capabilities that most end users don’t have any idea how to set them up or change them; in fact, many end users don’t even know they have an automixer in their facility. “The ideal automixer is transparent to the end user,” says Jim Zagryn, design engineer at VisionPoint LLC, an integration firm in Newington, CT. “If the designers and integrators have done their jobs correctly, all of the end user’s needs are met during the system installation, and they never see the mixer.” As the name implies, an automatic microphone mixer manages multiple microphones automatically, activating the microphones when someone speaks into them while keeping the other microphones at a reduced level (or off). This provides a consistent signal to the rest of the sound system and helps mitigate room noise and reverberation. Automixers are used in many different applications, and a number of manufacturers make them. They were first developed in the 1970s by Dan Dugan of Dan Dugan Sound Design in San Francisco. “I was designing sound for the regional companies of Hair in 1968. The shows had one of mixing that will work best for a particular application. Automatic microphone mixers are used in any “spoken word” application requiring several microphones, but the primary applications fall into two categories: collaboration (two or more sites doing audio or video conferencing) and “local” uses such as broadcast studios, auditoriums, conference/meeting rooms, legislative chambers, courtrooms, or houses of worship where the automatic mixer feeds the main audio system. All applications usually require some sort of sound reinforcement within the facility. Mixers specifically designed for conferencing incorporate functions that are required to improve audio clarity between sites — acoustic echo canceling, ambient noise reduction, etc. Manufacturers such as Biamp, ClearOne, and Polycom make mixers that include “distributed echo cancellation,” or an acoustic echo canceler on every microphone input. Lectrosonics uses its own patented algorithm called “AutoSkewing,” PROPERLY CONFIGURED, THESE AUDIO ENGINEERS IN A BOX CAN SIMPLIFY ANY MULTIPLE MICROPHONE AUDIO SYSTEM. person working rotary knobs for 16 area mics, 9 hand mics, and 10 mics in the band,” says Dugan. “I got the idea that a microphone shouldn’t be on unless it’s getting something more than the room ambience.” After several years of experimenting, Dugan came out with a patented system he called the “Dugan Music System” — which was demonstrated to the Audio Engineering Society in the early 1970s but didn’t evolve into a product immediately. He later developed the “Dugan Speech System,” which laid the groundwork for the “gain sharing” automixers used today. Dugan’s method of mixing, which sets a maximum gain for the room and then smoothly mixes all microphones by splitting the overall room gain among all open microphones based on the signal levels at the microphone inputs, was patented by Dugan in 1975. Other manufacturers (such as Shure), recognizing the benefits of automatic mixing, soon developed an alternate mixing technique known as “adaptive threshold gating,” where a microphone is activated based on the ratio of the audio level at the mic vs. ambient room level. “Each mixing method has its benefits,” says Zagryn. “I personally prefer gated microphones to provide control over the number of people who are on at once, and gated systems keep room noise down, but there can be a bit of delay before someone’s voice comes on so gated systems can be a bit choppy. Gain sharing mixers are much smoother but there’s more noise floor — more ambient noise is picked up by microphones.” Dugan’s gain sharing patent expired several years ago, and now manufacturers such as Polycom and Lectrosonics incorporate their own techniques of gain sharing in their mixers. Some manufacturers provide both gating and gain sharing, giving integrators and users the option to set up the type www.avtechnologyonline.com which uses the amplitude, frequency, and time domain information of a signal to establish a pattern for a microphone, and then prevents other inputs in the system from opening that same signal, preventing “false” channel activation. Other manufacturers use the output of a gated automixer fed to a single-channel acoustic echo canceler for conferencing applications. Mixers made for “local” use do not need acoustic echo cancellation, and many products are much less expensive as a result. Companies such as Shure, Dan Dugan Sound Design, Lectrosonics, AKG, Audio-Technica, IED, Intelix, Rane, and others manufacture automixers that are used in a wide range of single-site applications. (Many of these manufacturers say their mixers also work well for audio and video conferencing — it all depends on the user’s needs, the room configuration, and the setup of the system, according to these companies.) Automatic microphone mixers are available in analog format and in DSP-based configurations. Analog units offer smooth scalability for large applications — for example, Shure mixers can handle up to 400 microphones in a single linked system. DSP units, on the other hand, are packed with features that greatly enhance their ability to work in widely varied conditions. DSP units offer presets and macro functions that enable rapid changing of the system to meet varying requirements in the room (for example, a hotel ballroom that might need to be sub-divided and then re-combined later in the day). SETTING UP AN AUTOMIXING SYSTEM If you are using an automatic mixer for live sound applications, such as august 2008 | AV TECHNOLOGY | 25 http://www.avtechnologyonline.com

Table of Contents Feed for the Digital Edition of AV Technology - August 2008

AV Technology - August 2008 Contents Precedent Corporate: The Project’s Over...Now What? Government: Generational Diversity and the Rise of the Millennials Education: DIY ISP.EDU HD Videoconferencing On a Budget Using Automatic Mic Mixers The Way I See It: The Standards Dilemma in AV Something for Everybody AV Adds the Magic to Microsoft’s Hat Trick Simple Control for Smarter Classrooms Product Review: VeEX VePAL MX100 Product Spotlight: Amps; Touchpanels New Products Ad Index AV MO: Dealing with Ambient Light

AV Technology - August 2008

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