Mixing console


A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summed to produce the combined output signals, which can then be broadcast, amplified through a sound reinforcement system or recorded.
Mixing consoles are used for applications including recording studios, public address systems, sound reinforcement systems, nightclubs, broadcasting, and post-production. A typical, simple application combines signals from microphones on stage into an amplifier that drives one set of loudspeakers for the audience. A DJ mixer may have only two channels, for mixing two record players. A coffeehouse's small stage might only have a six-channel mixer, enough for two singer-guitarists and a percussionist. A nightclub stage's mixer for rock music shows may have 24 channels for mixing the signals from a rhythm section, lead guitar and several vocalists. A mixing console in a professional recording studio may have as many as 96 channels. Consoles used for live sound can go even higher, with some having up to 384 input channels.
In practice, mixers do more than simply mix signals. They can provide phantom power for condenser microphones or active DI boxes; pan control, which changes a sound's apparent position in the stereo field; filtering and equalization, which enables sound engineers to boost or cut selected frequencies to improve the sound; dynamic range compression, which allows engineers to increase the overall gain of the system or channel without exceeding the dynamic limits of the system; routing facilities, to send the signal from the mixer to another device, such as a sound recording system or a control room; and monitoring facilities, whereby one of a number of sources can be routed to loudspeakers or headphones for listening, often without affecting the mixer's main output. Some mixers have onboard electronic effects, such as reverb. Some mixers intended for small venue live performance applications may include an integrated power amplifier.

Terminology

A mixing console is also known as an audio mixer, audio console, mixing desk, sound mixer, soundboard, or simply as a board or mixer.

Structure

An analog mixing board is divided into functional sections. Some of the more important functional sections are subdivided into subsections.

Channel input strip

The channel input strips are usually a bank of identical monaural or stereo input channels arranged in columns. Typically, each channel's column contains a number of rotary potentiometer knobs, buttons, and faders for controlling the gain of the input preamplifier, adjusting the equalization of the signal on each channel, controlling routing of the input signal to other functional sections, and adjusting the channel's contribution to the overall mix being produced.
The types of inputs that can be plugged into a mixer depend on the intended purpose of the mixer. A mixer intended for a live venue or a recording studio typically has a range of input jacks, such as XLR connectors for microphones and the outputs from DI boxes, and 1/4" jacks for line level sources. A DJ mixer typically has RCA connector inputs for pre-recorded music being played back on turntables or CD players, and a single mic input.
Depending on the mixer, a channel may have buttons that enable the audio engineer to reroute the signal to a different output for monitoring purposes, turn on an attenuator pad, or activate other features, such as a high-pass filter. Some higher-priced mixers have a parametric equalizer or a semi-parametric equalizer for one or more of the equalizer frequency bands, often the middle range.
The channel strips are typically numbered so that the audio engineer can identify the different channels. For each channel input, a mixer provides one or more input jacks. On consoles for mid- to large-sized live venues, and sound recording consoles, these input jacks are numbered and consolidated in a patch bay. On smaller mixers, the input jacks may be mounted on the top panel of the mixer to facilitate the connection and disconnection of inputs during the use of the mixer.
The input strip is usually separated into sections:
On many consoles, these sections are color-coded for quick identification by the operator. Each signal that is plugged into the mixer has its own channel. Depending on the specific mixer, each channel is stereo or monaural. On most mixers, each channel has an XLR input, and many have RCA or quarter-inch TRS phone connector line inputs. The smallest, least expensive mixers may only have one XLR input, with the other inputs being line inputs. These can be used by a singer-guitarist or other small acts.

Basic input controls

The first knob at the top of an input strip is typically a trim or gain control. The input/preamp conditions the signal from the external device and this controls the amount of amplification or attenuation that is applied to the input signal to bring it to a nominal level for processing. Due to the high gains involved, this stage is where most noise and interference is picked up. Balanced inputs and connectors, such as XLR or phone connectors that have been specifically wired as balanced lines, reduce interference problems.
A microphone plugged directly into a power amplifier would not produce an adequate signal level to drive loudspeakers, because the microphone's signal is too weak; the microphone signal needs a preamplifier to strengthen the signal so that it is strong enough for the power amplifier. For some very strong line level signals, the signal that is plugged into the mixer may be too strong, and cause audio clipping. For signals that are too strong, a 15 dB or 20 dB pad can be used to attenuate the signal. Both preamplifiers and pads, and the controls associated with them, are available in the input section of most mixing consoles.
Audio engineers typically aim at achieving a good gain structure for each channel. To obtain a good gain structure, engineers usually raise the gain as high as they can before audio clipping results; this helps to provide the best signal-to-noise ratio.
A mixing console may provide insert points after the input gain stage. These provide send and return connections for external processors that only affect an individual channel's signal. Effects that operate on multiple channels connect to auxiliary sends.

Auxiliary send routing

The auxiliary send routes a split of the incoming signal to an auxiliary bus, which can then be routed to external devices. Auxiliary sends can either be pre-fader or post-fader, in that the level of a pre-fader send is set by the auxiliary send control, whereas post-fade sends depend on the position of the channel fader as well. Auxiliary sends can send the signal to an external processor such as a reverb, with the return signal routed through another channel or designated auxiliary return. Post-fader sends are normally used in this case. Pre-fade auxiliary sends can provide a monitor mix to musicians on stage ; this mix is thus independent of the main mix produced by the faders.
Most live radio broadcasting soundboards send audio through program channels. Most boards have 3-4 program channels, though some have more options. When a given channel button is selected, the audio will be sent to that device or transmitter. Program 1 is typically the on-air live feed, or what those listening to the broadcast will hear. Other program channels may feed one or more computers used for editing or sound playback. Another program channel may be used to send audio to the talent's headset if they are broadcasting from a remote area.

Channel equalization

Further channel controls affect the equalization of the signal by separately attenuating or boosting a range of frequencies. The smallest, least expensive mixers may only have bass and treble controls. Most mid-range and higher-priced mixers have bass, midrange, and treble, or even additional mid-range controls. Many high-end mixing consoles have parametric equalization on each channel. Some mixers have a general equalization control at the output, for controlling the tone of the overall mix.

Cue system

The cue system allows the operator to listen to one or more selected signals without affecting the console's main outputs. A sound engineer can use the cue feature to, for instance, get a sound recording they wish to play soon cued up to the start point of a song, without the listeners hearing these actions. The signal from the cue system is fed to the console's headphone amp and may also be available as a line-level output that is intended to drive a monitor speaker system. The terms AFL and PFL are used to describe, respectively, whether or not the level of the cue signal for an input is controlled by the corresponding fader. Consoles with a cue feature have a dedicated button on each channel, typically labeled Cue, AFL, PFL, Solo, or Listen. When cue is enabled on multiple channels, a mix of these signals is heard through the cue system.
Solo in place is a related feature on advanced consoles. It typically is controlled by the cue button, but unlike cue, SIP affects the output mix; It mutes everything except the channel or channels being soloed. SIP is useful for setup of a mixing board and troubleshooting, in that it allows the operator to quickly mute everything but the signal being adjusted. For example, if an audio engineer is having problems with clipping on an input, they may use SIP to solely hear that channel, so that the problem can be diagnosed and addressed. SIP is potentially disastrous if engaged accidentally during a performance, as it will mute all the channels except one, so most consoles require the operator to take very deliberate actions to engage SIP.