Sound Mixing Boards for Theatre

Over the years, theatrical technology has progressed immensely. One of these advancements includes the mixing console. A mixing console is an electronic device that is used for combining, routing, changing the level, timbre and/or dynamics of audio signals. Depending on the type of mixer, a mixer can mix either analog or digital sounds. The altered signals are then summed together in order to produce the collective output signals. In 1958, the Willi Studer Company of Switzerland manufactured one of the earliest mixing consoles. This device, called the “Studer 69,” used reel-to-reel tape and was portable. While this particular console was portable, these early devices were still bulky. As technology advanced, mixing consoles became lighter and more compact, which allowed for the inclusion of more features and capabilities. (Coe, 2009) Research by Coe (2009) demonstrates that mixing consoles started out in the 1950s as purely analog, devices with only one or two channels. As more purposes for mixing consoles appeared, more options began to develop. Transformations in electronics supplied the digital technology needed for these new functions. While digital mixing consoles have more features, many users still prefer analog mixers due to their ease of use. Hybrid mixing consoles, combining both digital and analog inputs into one piece of hardware, retain the advantages of the old while also integrating the features of the new. Traditional analog mixers combine signals using analog techniques. On an analog mixer, each of the inputs has a fader that feeds into a master amplifier. The master amplifier also has a fader that controls the overall loudness. These sounds are combined, routed and modified as electrical signals. A digital mixer takes each sound signal input and converts it to a rapid stream of numbers called analog-to-digital conversion, or ADC. The mixer combines, routes and processes the numbers with computer software. At its output, the digital mixer converts the numeric information back to standard electrical signals. This conversion is typically referred to as digital-to-analog conversion, or DAC. Digital mixers have many of the physical features of analog models, including faders, knobs and switches, but internally the circuits are very different. (Barett, 2010) According to Barett (2010) the circuits that convert sound signals to numbers in a digital mixer produce a small amount of signal delay called latency. The delay time depends on the equipment and its settings. Analog mixing consoles process sound immediately and do not experience latency. Analog circuits must be carefully designed and used to avoid noise. All circuits create a small amount of hiss that is faintly present. More analog circuits means more chances for noise to build up. They can also pick up electrical interference from computers, cell phones and other sources. Digital circuits are less susceptible to this kind of noise seeing as the mixer's input and output signals are conducted as numbers.
Many of a digital mixer's features are done as software programs. As a result, the capability of the mixer is less dictated by its physical hardware than an analog mixer’s. Designers can create hundreds of sound effects, filters and ways to control the dynamics of the sound's loudness. It is much easier to automate a digital mixer than an analog one, especially since the engineer can store, recall and fine-tune entire mixing sessions. Many digital mixers have virtual controls that let the user route and mix sounds in ways that would be otherwise impossible. (Barett, 2010) Mixing consoles are utilized for many different purposes, one including sound reinforcement systems for live performances, such as theatre. For example, in the theatre setting mixers are used to empower the signals that originate from multiple microphones being used by actors to be heard through multiple sets of speakers concurrently. During these live performances, the signal produced by the mixer is typically sent directly to an amplifier unless the mixer is powered or being connected to powered speakers. (Scovill, 2012) The typical layout of a mixing console consists of multiple channel input strips. These input strips are typically a row of identical monaural, also referred to as mono, or stereo input channels. The section of the mixer known as the master control section contains sub-group faders, master faders, master auxiliary mixing bus level controls as well as auxiliary return level controls. Aside from these controls there may also be solo monitoring controls, a stage talkback microphone input/control, muting controls and an output matrix mixer. The inputs on smaller mixers are usually located on the left of the mixing board while the master controls are on the right. The master controls on larger consoles are normally located in the center of the console, with the inputs surrounding them on both sides. Above the input and master sections is typically where the audio level meters are located, but they may be incorporated into the input and master sections as well. (“How to Use an Audio Mixer”) The input strip is generally separated into the following sections: input jacks, microphone preamplifiers, equalization, dynamics processing, routing and input faders. These sections are color-coded on most consoles for easy identification by the operator. Each signal that is inputted into the mixer has its own channel. These channels are either monaural or stereo depending on the mixer. The channels on most mixers have an XLR input, and many also have RCA or quarter-inch tip ring sleeve phone connector line inputs. (Scovill, 2012) Located below each input are generally several rotating control knobs. The trim or gain control is usually the first of these controls. The inputs moderate the signal from the sound source and the trim or gain controls the amount of amplification or reduction needed for the signal to be at a nominal level for processing. Most noise and interference occurs due to high gains. One way to reduce interference problems is by using balanced inputs and connectors, such as XLR or phone connectors. After the gain phase there may be insert points that send to and return from external processors. These processors should only affect the signal of the particular channel that the insert is plugged into. When there are effects that are utilized on multiple channels, they are connected to the auxiliary sends. (“How to Use an Audio Mixer”) An auxiliary send splits the incoming signal to an auxiliary bus that can then be sent to external devices. These aux sends can either be run pre-fader or post-fader. A pre-fader send is set and adjusted by the auxiliary send control. A post-fader send is set and adjusted by the auxiliary send control, in addition to the channel fader. In theatre, auxiliary sends can be used to send the signal to an external processor to add effects such as reverberation. This signal is then routed back through a separate channel designated for auxiliary returns on the mixer. These effects are typically run in post-fader, while auxiliary sends that are used to provide a monitor mix to musicians or the pit are run in pre-fader. (“The Mixing Board”) The equalization channel control affects the equalization of the signal by individually either boosting or cutting a specific range of frequencies. Most mixing consoles have a parametric equalizer dedicated to each individual channel. Some mixers have a general equalization control that affects the entire output signal. This equalization is generally either parametric or graphic. (“The Mixing Board”) Most mixers have a built-in cue system that allows the engineer to listen to any of the signals without affecting the output signals from the console. This signal is then sent to the mixer’s headphone jack and can sometimes also be routed to a line-level output that is designed for a monitor speaker system depending on the console. Typically associated with the cue system are the terms pre fade listen, also knows as PFL, and after fade listen, also known as AFL. The input channels are generally configured to PFL so the operator can listen to the signal from the channel without sending it to the outputs or any other mix. Mixers with this feature will have a dedicated button with the label cue, AFL, PFL, solo, or listen located on each of the channels. (“How to Use an Audio Mixer”) Found on more advanced consoles are a similar feature known as solo in place, or SIP. The cue button generally controls this function as well, but unlike cue, solo in place is damaging to the output mix. The purpose of solo in place is to mute everything on the console except the channel or channels that are cued. This is useful for trouble-shooting because it allows the engineer to promptly mute everything except for the signal being worked on. Solo in place is a function that could be extremely hazardous to an engineer’s entire mix if engaged during a live performance. Because of this, most consoles require intricate steps to engage the solo in place feature. (“How to Use an Audio Mixer”) For each channel on a mixer there is a sliding volume control, or fader, that adjusts the level of the channel. The signals from each channel are summed together to formulate the main mix. Sometimes these signals are combined on a bus as a sub-mix, which is essentially just a group of channels that are added to achieve the final mix. It is also common for there to be insert points for a certain bus or for the entire mix itself. (Scovill, 2012) More advanced consoles have voltage-controlled amplifier, or VCA, groups that operate very similarly to subgroups. When utilized, these groups let the operator control the level of multiple input channels with just one fader. While subgroups create sub-mixes, VCA groups do not. The signals from the channels that are assigned to the VCA continue to be transmitted independently of VCA assignments. Seeing as there is no sub-mix being created, inserting processing into VCA groups is not possible. (“How to Use an Audio Mixer”) As mentioned previously, subgroup and main output faders are typically located collectively on the right side of the mixer on smaller consoles and in the center surrounded by inputs on larger consoles. Headphone, talkback and monitoring controls are also located in this master section in addition to matrix routing controls. The talkback function allows the operator to converse with talent through monitors, headphones, or any type of in-ear monitoring device. On some mixers there is a test tone generator located in the master output section. Lastly, aux returns are generally located in the master section as well. (“How to Use an Audio Mixer”) Last but not least, located on every console is one or more VU or peak meter that shows the levels for each individual channel, the master outputs and to show whether or not the console levels are clipping the signal. Many mixers have at least one extra output in addition to the main mix. These additional outputs are either individual bus outputs or auxiliary outputs. Mixing console controls and displays are more often than not displayed in decibels, a logarithmic measurement system consisting of both amplitude and frequency. Seeing as decibels are a relative measurement and not a unit itself, the meters need to be oriented to a nominal level. The considered professional nominal level is +4 dBu while the consumer grade level is -10 dBV. (Scovill, 2012)

Works Cited
Barett, J.T. "Analogue Vs. Digital Mixers." EHow. Demand Media, 14 Apr. 2010. Web. 23 Apr. 2014.
Coe, Robin. "The History of Mixing Consoles." EHow. Demand Media, 11 Oct. 2009. Web. 23 Apr. 2014.
"How to Use an Audio Mixer (soundboard)." Instructables.com. N.p., n.d. Web. 23 Apr. 2014.
"The Mixing Board - A Quick Guide To How It Works." Practical Music Production. N.p., n.d. Web. 23 Apr. 2014.
Scovill, Robert. "Church Sound: Mixing Console Management - Pro Sound Web." Church Sound RSS. N.p., 6 Dec. 2012. Web. 23 Apr. 2014.