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Boundary Mics and Automatic Mixers

Sep 15, 2010 12:12 PM, By Mark Johnson

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Automatic Microphone Mixers: Keeping It Under Control
Now that you’ve chosen the mics that fit the needs of your specific application/installation, how do you control them? The situation is especially problematic in a boardroom or conference room environment where having an operator on hand is often not practical—or even desired.

At the most basic level, an automatic mic mixer turns up the specific microphone (or microphones) that are in use, while the remaining mics are off or at a low level, and overall system gain is adjusted to avoid feedback. This can be accomplished with approaches as simple as a noise gate, ranging to adaptive threshold sensing and gain reduction systems. Depending on the manufacturer and model, analog and/or digital circuitry is used. Most of the units available can be linked to provide more input automixing capability.

Dan Dugan is generally acknowledged as the inventor of the automatic mixer, debuting his Dugan System Model A mixer in 1971. Quite a lot has transpired since then, and it’s now a competitive marketplace with a lot of choices. We examined a selection of current offerings that employ divergent approaches to the technology from a variety of manufacturers.

Audio-Technica AT-MX381 SmartMixer

Audio-Technica AT-MX381 SmartMixer

The latest addition to Audio-Technica’s family of automatic mixers, the 8-channel AT-MX381 SmartMixer features three different priority selection/operation modes. Basic functions (such as line/mic input switching, phantom power, gain, and low-cut filters) can be set from the unit itself with more in-depth control available via an RS-232 data post using the included SmartMix PC software. The unit is rackmountable and compatible with Crestron and AMX systems. Up to 16 AT-MX381 units can be linked for up to 128 inputs.

Biamp’s Systems autoTwo is an 8-channel mic/line mixer that features channel 8 mix-minus assign and ducking via channels 1 through 7. The unit also features logic outputs for switching of external circuits, adaptive threshold-sensing speech frequency filtering, and manual priority override. Also standard is selectable channel-off attenuation, selectable last mic hold, and full compatibility with all other Biamp products. Two units can be cascaded for up to 16-input operation.

The ClearOne Converge SR 1212 is an advanced automatic digital mixer with ClearOne’s fourth-generation audio processing technologies. This 12x12 (in/out) automatic digital mixer has eight mic/line inputs and four line inputs. The unit features USB and Ethernet connectivity and drag-and-drop configuration software. Multiple units within the Converge family can be linked for additional flexibility and/or input control, 32 presets can be executed on-the-fly, and 255 macros allow customized audio control and configuration with single command execution.

Clockaudio MR88

Clockaudio MR88

The Clockaudio MR88 digital automatic mixer is a DSP microprocessor-controlled, automatic switching, 8-channel microphone mixer that provides eight mic/line inputs, two outputs, and individual unbalanced outputs from each of the mic preamps for recording feeds. The MR88 can be daisy-chained with other MR88 mixers when more than eight microphones are required to create a multimixer system, or the system can function as a standalone 8x2 mixer. Input channels can be set to a multilevel priority system, allowing for one-at-a-time operation, all channels active, or combinations with chairman priorities.

The Dan Dugan Sound Design D-2 automatic mixing controller is designed for insertion into up to eight channels on a mixing console to use the functions of the mixer while taking advantage of the controller’s automatic mixing capabilities. The system is composed of a 2RU processor with all the I/O connections and a separate mix control panel. The D-2 combines three patented technologies—the Dugan Speech System, the Dugan Music System, and the Dugan Gain Limiting System—to provide transparent mic control under nearly any situation. Built-in expandability allows linking units for up to 64 channels.

The Lectrosonics DM84 digital matrix processor is an eight-in/four-out automatic matrix mixer. Each input has six filters and six feedback eliminators, with compression and delay available. Other features include eight mic/line inputs and four mic/line outputs; switchable phantom power; programmable front-panel control knobs for easy I/O gain adjustment; input and output channel activity indicators; and automatic mic mixing with proportional gain and auto­skew. The unit is AMX- and Crestron-compatible with USB and RS-232 interfaces for setup and control.

The Peavey Architectural Acoustics Automix Control 8 offers eight transformer balanced mic/line inputs. The first two channels feature a priority control and each channel has a phantom power (on mic inputs), low-cut filter, aux send control, and can be set for manual and auto operation. Each channel also has an insert point and 5V TTL status output. Multiple channels can be muted simultaneously via an assignable mute bus. Several units can be linked to form a single mixer with 16, 24, 32, or more inputs, and the Automix Control 8 includes a see-through Plexiglas security panel to prevent unauthorized changes.

Rane AM1

Rane AM1

Part gain-sharing automatic mic mixer, part manual line mixer, part USB audio I/O device, the Rane AM1 is a 4-channel unit that features additional aux inputs as well as USB I/O. Each of the four XLR mic inputs offers level controls feeding a gain-sharing automatic mixer, or it can be used as a standalone mic mixer. Expansion for more gain-shared mics is possible using up to seven Rane AM2 automixers, and a RAD port allows transport the main mix via a Rane Mongoose to a CobraNet network. The AM1 shows up as a standard USB audio device on Windows and Apple computers and is compatible with many audio recording and playback apps.

The Shure SCM810 8-channel automatic microphone mixer features noise adaptive threshold to distinguish between constant background noise and audio signal fluctuating in pitch, level, and consistency (speech). All inputs are balanced and provide phantom power for condenser mics. Low-cut filter and high-shelving EQ is provided on all input channels along with direct outputs on each mic/line input as well as a peak responding output limiter with selectable thresholds on the main output. Seven position-programmable switches offer further tweaks to internal features, and the mixer can be switched between manual and automatic modes.

TOA Electronics D-901

TOA Electronics D-901

The TOA Electronics D-901 is a modular 12-input, eight-bus, eight-output system with a variety of input modules available and RS-232 or contact-closure remote control. EQ and filter settings can be saved in up to 16 internal memories and the unit can be controlled using AMX or Crestron devices. Onboard processing tools include automixing, feedback suppression, multiband parametric EQ, compressors/limiters, gates, crossovers, and delays. The D-201 is programmable from the front panel or using included PC control software and can be set up and preconfigured offsite and updated onsite.

Mark Johnson has been involved with audio and video for more than 35 years, including production, manufacturing, and covering the industries for various publications.

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