In professional audio, an automixer is a hardware or software device that balances multiple sound sources, usually microphones, based on each source's level, quickly and dramatically [ [ Rane Pro Audio Reference. "A: automatic mic mixer"] ] attenuating inactive inputs on the fly to deliver a more focused and intellibible mix that has less hiss, rumble, reverberation and noise. Automatic microphone mixers use a variety of protocols that allow increased gain before feedback for live sound reinforcement as well as reducing comb filtering between multiple microphones for recorded and broadcast applications. [ Sound & Video Contractor. Allan Soifer. "Automatic Mic Mixers" May 2003] ]

Automixers are typically used to mix panel discussions on television shows and at conferences and seminars. They can also be used to mix actors' wireless microphones in theater productions and musicals. They are frequently employed in commercial sound systems such as in courtrooms and city council chambers where it is not expected that a live sound operator will be present to mix the microphones. Wherever automixers are used in live sound reinforcement, their main benefit is that they work to maintain a steady limit on the overall signal level of the microphones; if a public address system is set up so that one microphone will not feed back, then, in general, multiple microphones will not feed back if they are automixed. The equivalent number of open mics (NOM) present at the output of the automixer is kept low, regardless of the actual number of open mics. [ [ Sound & Video Contractor. Dan Dugan. "The Right Mix: The applications of automatic microphone mixers are numerous and varied; know when and how to use them properly." January 1998] ]

A skilled audio mix operator can greatly enhance the performance of a sound reinforcement system but will never be able to anticipate with perfect accuracy which participant will speak next in a free-wheeling discussion. Sudden interjections by panelists may be lost completely, or the beginning of a word may be absent until the operator responds as quickly as humanly possible to fade up their audio signal (this loss of the beginning is called "upcut"). [ [ Alex Epstein. 2006. "Crafty TV Writing"] ] A properly adjusted automixer can help in avoiding lost words or phrases due to upcut mistakes or lapses of attention. [ [ Whitepapers. Tom Stuckman, Steve Marks. "Automatic Mixers".] ]


Frank J. Clement and Bell Labs received a patent in 1969 for a multiple station conference telephone system that switched its output to the loudest input. [Cite patent|US|3437758] The next year, Emil Torick and Richard G. Allen were granted a patent for an "Automatic Gain Control System with Noise Variable Threshold", an adaptive threshold circuit invention with its patent assignation going to Columbia Broadcasting System. [Cite patent|US|3496481]

Some systems using electro-mechanical switching in regard to microphone activation were engineered in the late 1960s and early 1970s. Peter W. Tappan and Robert F. Ancha devised a system of seat sensors that would activate one of 350 hidden microphones at the Seventeenth Church of Christ, Scientist in Chicago in 1970. [Cite patent|US|3538254 ] From approximately 1968, Ken Patterson and [ Diversified Concepts] developed a hardware system that could detect the "Number of Open Microphones" (NOM) and attenuate the master output by an amount which increased with a higher number of microphones in use. This latter system was public domain. [ [ AES E-Library: Dan Dugan. "Application of Automatic Mixing Techniques to Audio Consoles". October, 1989] ]

In 1971, Gregory Maston of Bell Labs filed for a patent involving a circuit that could switch between several audio sources based on their levels. The loudest one was latched into the mix. This system did not ramp switched signals smoothly in and out and did not maintain a constant ambience. It was intended for speakerphone conferencing applications. [Cite patent|US|3755625] In 1972, Keith A. T. Knox with the British Post Office Corporation developed an adaptive threshold gate circuit intended for speakerphone usage. The system used a second microphone somewhat near the first to sense ambient noise level. [Cite patent|CA|893261]

Daniel W. "Dan" Dugan began manufacturing his first automixer system, the Model A, in 1971. [ [ Dan Dugan Sound Design. "Introduction: The World's Finest Automatic Microphone Mixers"] ] Dugan built 60 units, with the first, hand-assembled one taken to Bell Labs to be installed in their conference room for Harvey Fletcher. [ Live Design Online. June 1, 2008. Shannon Slaton. "Sound Product Of The Month: Dugan Model E-1 Automatic Mixing Controller"] ] Dugan showed his first "Adaptive Threshold Automatic Microphone Mixing System" in 1974 at the 49th Audio Engineering Society (AES) meeting in New York, [ [ AES E-Library. Dugan, Daniel W. "Adaptive Threshold Automatic Microphone Mixing System Becomes Public Domain". February 1991.] ] and was granted a patent for a control apparatus for sound reinforcement systems which sensed ambient sound level in the environment of a theater to control each microphone's individual level. [Cite patent|US|3814856] In 1976, Dugan was granted a patent for an automatic microphone mixing process whereby the total gain of the system remains constant. [Cite patent|US|3992584] The algorithm was elegantly simple: "Each individual input channel is attenuated by an amount, in dB, equal to the difference, in dB, between that channel’s level and the sum of all channel levels." [ [ Protech Audio. "The Path Less Taken - Dugan Automixing."] ] Dugan licensed the system to Altec who released several automixer models including the 1674A, -B and -C series and the 1684A, all focusing on speech applications. [ [ Altec 1674C product sheet.] ] [ [ Altec 1684A product sheet.] ] (The 1684A became an Electrovoice product and is currently administered by their Commercial division. [ [$file/1684A-eds.pdf Electrovoice Commercial. 1684A Expandable Automatic Microphone Mixer] ] ) The Altec product implementation was regarded as inferior within the commercial audio contractor industry, and other manufacturers began to design their own automixer products.

In 1978, Richard W. Peters of Industrial Research Products (IRP) was granted an improvement patent entitled "Priority mixer control". [Cite patent|US|4149032] IRP released the Voice-Matic series of 4x1 and 8x1 automatic mixers using "Dynamic Threshold Sensing" that weighed a combination of the amplitude and history of the signal to determine channel access. The master output was attenuated at the rate of 3 dB for every doubling of NOM. [ [ Industrial Research Products. Automatic Mixers. "Voice-Matic"] ]

Eugene Campbell and Terrance Whittemore of Colorado were granted a patent in 1982 for an automatic microphone mixing algorithm that allowed for musical performance mixing that would not be dominated by the loudest vocalist or instrumentalist. [Cite patent|US|4357492]

Stephen D. Julstrom of Shure Brothers, Inc. (Evanston, Illinois) was granted a patent in 1987 for a teleconferencing system that used special directionally gated microphones mixed automatically and sent to a distant party via telephone line. The return signal from the distant party was compared in strength to the local mix to determine which party was to be most prominent in the overall mix. Any interrupting party was given priority. [Cite patent|US|4712231] Four years later, Shure would introduce the AMS4000 and AMS8000 automixers for sound reinforcement; mixers which required the use of special directional condenser microphones of the Shure AMS Series. [ [ Shure discontinued products. Datasheet: "AMS4000 and AMS8000"] ]

At the 87th AES Convention in 1989, Dugan introduced the idea of using an automixer inserted within target channels on a professional audio mixer. Each microphone's signal would be interrupted inside its channel strip and sent to a variable gain circuit contained within the automixer. The signal would then be returned to the mixer at a level consistent with the Dugan algorithm. [ [ AES E-Library. Dan Dugan "Application of Automatic Mixing Techniques to Audio Consoles". October 1989.] ] This became the Dugan Model D automixer. [ [ Dan Dugan Sound Design. "Model D"] ]

In 1991, Dugan's patent expired. Competing manufacturers began to bring the Dugan algorithm directly to their product designs. In 1993, Travis M. Sims, Jr. of Lectrosonics (Rio Rancho, New Mexico) was granted a patent for a sound system with rate controlled, variable attenuation of microphone inputs, including the Dugan algorithm as well as loudspeaker zone attenuation when in close proximity to an active microphone. [Cite patent|US|5204908] The loudspeaker zone part of the patent cited a 1985 patent for proportional amplification by Eugene R. Griffith, Jr. of LVW Systems of Colorado Springs, a commercial audio contractor. [Cite patent|US|4598418 ] In 1995, Sims and Lectrosonics gained another patent for an "Adaptive proportional gain audio mixing system" which incorporated a number of ideas including the Dugan algorithm for maintaining a constant total gain of all the inputs. [Cite patent|US|5414776]

In 1996, Dugan came out with the Model D-1, a speech-only economy model that did not offer the music system of the Model D.

In 1997, John H. Roberts of Peavey Electronics was granted a patent for an automatic mixer priority circuit, enabling a hierarchy of logic weighting that allowed selected signals to push forward in the mix when they are in use, while still maintaining the useful constant unity, gain-sharing relationship first described by Dugan. The hierarchy enabled a host, moderator or chairperson to speak over other participants and retain control of the discussion. [Cite patent|US|5652800] Peavey's Architectural Acoustics division used three levels of hierarchy in their 1998 "Automix 2" product, placing the first- and second-most influentially-weighted sources at inputs 1 and 2, respectively. [ [ Archived product manuals. "Automix 2 - 8 Channel Automatic Mixer"] ]

Dan Dugan licensed his system to Protech Audio (Indian Lake, New York) in 1997, yielding the Protech 2000 model series. [ [ Protech Audio. "Dugan Automixers - The World's Best Automixers"] ]

In 2004, the first standard audio mixer incorporating an eight-channel automixer section was released by Peavey in their Sanctuary Series, [ [ "Peavey Innovations Timeline"] ] and in 2006 the similar HP-W was introduced by Crest. [ [ Harmony Central. July 15, 2006. "Crest Audio Introduces The HP-W Professional Mixing Console"] ] Both mixers were aimed at the House of Worship market, adding functions that ease the process of audio mixing to religious organizations.

In 2007, Mark W. Gilbert and Gregory H. Canfield of Shure (Niles, Illinois) were granted a patent for a digital microphone automixer system that used time of arrival as its main decision-making criteria. [ [ US patent 20070191977: "Digital Microphone Automixer"] ] [ [ World Intellectual Property Organization. "(WO/2007/090010) A DIGITAL MICROPHONE AUTOMIXER"] ]

Related applications

*Speech intelligibility enhancement, James M. Kates of Signatron (1984). This system uses Dugan's automatic mixing algorithm to reconstitute several spectral regions of a signal that has been divided into frequency bands for short-time spectral analysis in order to achieve greater intelligibility of spoken consonants. [Cite patent|US|4454609]

*Secure conferencing, patent by Raoul E. Drapeau (1993). An automixing algorithm attempts to mask incidental speech that is below automix threshold but which can be audible in the mix. The automix circuitry indicates which sources are active and if masking of low-level signals is occurring. [Cite patent|US|5197098]

Automixer manufacturers and products

*AKG Acoustics; AS8 [ [ AKG AS8 AutoMixer] (Adaptive proportional gain) (Adaptive Skewing) (Compressor Leveler)]
*Audio-Technicaa; AT-MX341a SmartMixer.
*beyerdynamic; MCS 100
*biamp; Audia [ [ Biamp "Audia"] ]
*Crest Audio; HP-W [ [ Crest HP-W mixer with automix] ]
*Crown; USM-810
*Gentner, Comrex, ClearOne; Converge Series, XAP Series
*Dan Dugan Sound Design; Models A, D, D-1, D-2, D-3, E and E-1 [ [ Dan Dugan Sound Design. "Model E-1"] ]
*Industrial Research Products; Voice-Tech
*Intelix; AMIX Series
*Ivie; AudioNet Automatic Matrix Mixers [ [ Ivie; AudioNet Automatic Matrix Mixers] ]
*Lectrosonics; LecNet2 Series [ [ Lectrosonics LecNet2. "DM Series Digital Audio Processors"] ]
*Peavey Electronics; Sanctuary, [ [ Peavey Sanctuary mixer with automix] ] Mediamatrix, NION, Automix 4, Automix 2, etc.
*Rane; RPM 88 [ [ Rane RPM 88] ]
*Shure; SCM410, SCM810, FP410
*Symetrix; SymNet Automixing [ [ Symetrix SymNet Applications. "Automixing"] ]
*TOA; AX-1000A, 9000 Series Digital Matrix Mixer/Amplifier [ [ TOA 9000 Series Digital Matrix Mixer/Amplifier] ]


See also

* Electronic mixer
* Variable-gain amplifier

External links

* [ Sound & Video Contractor. Bennett Liles. "Technology Showcase: Automatic Microphone Mixers" May 2007]

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