Engineering Data 10/11

The Protech Audio Model 2016 Automatic Mixer isdesigned specifically for small venues and rentalservice. The unit is designed around the patentedDugan Speech System.Much like an experienced console operator, theDugan algorithm allows turning up the gain on anactive channel, while simultaneously attenuatingunused channels. By subtracting additional gain fromunused channels, the unit reduces echo and redis-tributes that gain to active channels. This allowsgreater gain-before-feedback than gated mixers.

PROTECH®

Model2016

Automatic mixing with Dugan Speech System8 Mic/Line inputs with selectable gain structures2 AUX inputs with manual and auto modePhantom power switchable on each mic inputSignal Presence indicator on each inputClip indicator for summing busAssignable group mute on mic/line inputs12 segment LED metering of output levelRemote gain control capability on master outputU.S. Patent 3,992,584

DUGANAutomixer

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www.protechaudio.com

PROTECH

ARCHITECT'S & ENGINEER'S SPECIFICATIONThe automixer shall also have a 10 segment LED bar meter toindicate output level.The automixer shall have provision for assigning mic/line inputs toa group mute bus, via a DIP switch. A closure to ground shallactivate the group mute function.The master output shall be transformer isolated. The masteroutput level shall be controllable via a front panel potentiometer, ora remotely mounted potentiometer.The automatic mixer shall be: Protech Audio Corp. Model 2016

The automatic mixer shall use the Dugan Speech System ofautomatic mixing.The automatic mixer shall be constructed in a 1RU chassis,The unit shall be designed to mount in a standard 19" EIA rack.The auto-mixer shall have a UL approved power supply.Each automixer chassis shall accept up to 8 balanced microphoneor line level signals and 2 unbalanced line level inputs. The mic/line inputs shall be switchable between microhone or line leveloperation, and gain setting jumpers to allow adjustment of inputgain structure.The automixer shall have a visual indicator for signal presence oneach mic/line input and a clipping indicator that monitors all inputs

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INPUT SECTIONInput Gain Microphone...............................................................Input Gain Line..............................................................................AUX Input.....................................................................................Mute Attenuation.........................................................................Maximum Input Level..................................................................Input Impedance...........................................................................Group Mute Control..................................................................Phantom Power............................................................................Remote Control Range..............................................................OUTPUT SECTIONMaster/Slave Operation..............................................................Distortion + N..............................................................................Noise...............................................................................................Frequency Response....................................................................Operating Temperature.............................................................Power Requirement....................................................................Dimensions....................................................................................Shipping Weight............................................................................

30-50dB, switch selectable, plus front panel variable mix gain control 0-20dB, Adjustable0- 15dB 70dB, Min. -10dBvVMic, +20dBv Line 1K Ohms Nominal Mic, 15K Ohms Line DIP Switch Connection To Buss 15VDC +12dB, To -75dB

Slide Switch Controlled 0.07% Maximum -123dBV (150 Ohm Source) 30Hz To 20KHz, +0.1dB 0 To +70 Degrees C 0.5 Amps/120VAC 1.75"H x 19"W x 10.5"D Approx. 8 Lbs.

SPECIFICATIONS, MODEL 2016

MODEL 2016 AUTOMIXER

Meter

Output

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

MuteGainM/L Phantom

Detector VCA

Detector VCA

Detector VCA

Detector VCA

Detector VCA

Detector VCA

Detector VCA

Detector VCAP

P

P

P

P

P

P

P

AutomixControl

S VCAPot

Pot

Pot

Pot

Pot

Pot

Pot

Pot

Front PanelPot

RemotePot

L Transformer

Signal/Clip

BLOCK DIAGRAM

Inputs1-8

Mic/Line

The Model 2016 adds 2 AUX inputs that are summedto a common signal that is adjustable via a frontpanel control. The AUX inputs can be switchedbetween automatic and manual mode operation.Engineers at Protech Audio have worked directlywith Dan Dugan to develop circuitry that accom-plishes his algorithm economically and accurately,bringing transparent automixing to smaller instal-lations.For larger installations, Protech Audio manufac-tures the Models 2004, 2008, 2010, 2000 and 2000-C Automixers.

School Board MeetingsCouncil ChambersCourtroomsCorporate presentationHouses of WorshipBoard RoomsLegislative ChambersMeeting Rooms

Features Applications

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Protech Audio CorporationPO Box 597, 1158 Cedar River RoadIndian Lake, New York 12842Voice 518-648-6410 Fax 518-648-6395Web - www.protechaudio.com

Pot

Detector VCAAuto

Manual

AUX1 & 2

LED

LED

LED

LED

LED

LED

LED

LED

The mechanical architecture of the Model 2016allows input circuits to be configured quickly, fromthe rear of the unit.

The gain structure of each mic/line input has both a mic/line settings and a gain setting selectable via DIPswitches located on the rear of the unit . When the mic/line switch is placed into the LINE position, it places aresistive pad into the input circuit. Each input circuit hasa DIP switch position to select phantom power. Thephantom power voltage is 15VDC. Both the mic/lineswitch and the gain setting switch are placed ahead ofthe front panel level control, on each input. The frontpanel level control adjusts the mix level.

The gain setting switch adjusts the gain for either30dB or 50dB, in the MIC position, and 0dB or 20dB,when placed into the LINE position. This allows thegain structure to be tailored to the exact application,and optimizes the signal-to-noise ratio. The Model 2016is shipped from the factory with the gain settingjumper in the 50dB/20dB position.

Each mic/line input is assignable to a mute bus, via a 8position on the input DIP switch. If necessary all 8inputs can be assigned to the mute bus. Activation of themute function is via a remote closure.

The AUX inputs are summed to a common signal andmay be used in a manual or automatic mode.

The Model 2016 utilizes a unique clip indicator circuit.The circuit uses a bicolor LED that indicates bothsignal presence and clipping at the summing bus. Whenan input is about to be overloaded the LED changesfrom a green to a red color.

The master output of the Model 2016 is transformerisolated. Remote control capability of the outputlevel is built in. A simple 10K ohm potentiometer,mounted in a remote location, will control the outputlevel. Placing a resistor in series with the remotepotentiometer will restrict the overall range of theremote control.

A B

ba

Example 2 - Dugan MixingIn Figure 2, microphone “a” would be attenuated,while microphone “b” is in use. This will reduce thelevel of unwanted signals entering microphone “a”.This feature would be effective for all other micro-phones in the system. The effect is to greatly reduceroom echo. Another benefit of the Dugan mixing isthe gain reduction in the unused channels makesmore gain available in the active channel, resultingin a higher SPL for that signal, and a better signal-to-noise ratio.

Example 1- Gated Mixers.The gain of unused microphone channels wouldremain at a fixed level, even though another micro-phone channel is in use. This results in more back-ground noise pickup, or room echo effect fromspeakers A & B. It also limits the maximum gainavailable for the active channel, and a lower signal-to-noise ratio.

a b na b n

No Speech Mic b Active

a b na b n

No Speech Mic b ActiveGated Mixing

Wasted Gain & Increased Echo

Dugan Mixing

More Useable Gain & Echo Reduced

Dugan Vs. Gated Mixing

Figure 2.

In a boardroom, different talkers use differentmicrophones, and the signals entering these twomicrophones are totally unrelated to each other.These signals, which bear no relation to eachother are called “non-coherent” signals.A single talker, positioned an equal distance fromtwo microphones, produces an equal signal inboth microphones. Signals of this type arecalled “coherent” signals. Coherent signals do nothave to be equal in level, but do have to bevery similar. Another example of coherentsignals reaching two or more microphones resultswhen a door is slammed or a book is droppedat an approximately equal distance from two ormore microphones.The significance of coherent and non-coherentsignals is this: When two non-coherent signals

COHERENT AND NON-COHERENT SIGNALS

of equal level are mixed together, the resultantsignal is 3dB higher than either of the twooriginal signals. When two coherent signals ofequal level are mixed together, the resultantsignal is 6dB higher than either of the two origi-nal signals.If the design of an automatic mixer were tofail to recognize that coherent signals add differ-ently than non-coherent signals, the automaticmixer could potentially make serious mixing er-rors. It would even be possible for the poorlydesigned automatic mixer to cause the soundsystem to go into feedback, or create increasedacoustic echo amplification. The Dugan SpeechSystem correctly senses the presence of coherentsignals.

How does an accurate implementation of the DuganSpeech system algorithm result in superior audioperformance?First, the algorithm provides more useable gain toactive inputs. Unlike gating automixers, the DuganSpeech System subtracts gain from unused inputs,and makes that gain available to active inputs.Gating automixers leave that gain in the unusedinputs, and therefore cannot achieve the sameoutput level before feedback.Trying to process coherent signals also createsproblems for the gated automixers (see next page).A gated mixer does not recognize the differencebetween coherent and non-coherent signals. Theseartifacts are most noticeable in recorded proceed-ings, or teleconferencing applications.Second, by subtracting gain from unused inputs,and moving it to active inputs, the amount ofroom echo is greatly reduced. A gated mixerwould leave unused inputs at higher gain levels,and pick up more room noise. In using the Duganautomixers, the incoming teleconference signal isintroduced into the local mix bus. This will turndown the gain on the microphones while theincoming signal is present and greatly reduceacoustic echo.Perhaps the best way to describe the actual effectof the Dugan Speech System, would be tocompare it to an audio professional sitting at a mixposition. As an actor or entertainer walks across thestage, the person doing the mixing adjusts thefaders on different inputs, to follow the action.At some point the actor will be standing directlyin front of a single microphone, and the fader for thatchannel will be pushed to high gain, while thefaders for all the other channel will be pulled down.As the actor walks across the stage, leaving onemicrophone position and approaching another, themixer will pull down th fader for the one mic as heor she raises the fader for the new position. Noabrupt gain changes, just smooth transitions fromoneposition to the next. The Dugan Speech Systemdoes the same thing, automatically!

Dugan Operation Model 2016

Doing the math.

The original Dugan algorithm works on an elegantly simple principle. Each individual input channel

is attenuated by an amount, equal to the difference in dB, between that channel’s level andthe level of the sum of all channel before processing. It is a continuous computing function with nothreshold and no gating.