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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 , signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summation 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 , public address systems, sound reinforcement systems, , broadcasting, and post-production. A typical, simple application combines signals from microphones on stage into an amplifier that drives one set of 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; 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.
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 for microphones and the outputs from , and 1/4" jacks for line level sources. A DJ mixer typically has RCA connector inputs for pre-recorded music being played back on or , 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 (often reducing the signal by 15 or 20 dB to prevent audio clipping), 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 (e.g., a singer's vocal mic, the signal from an electric bass amp's DI box, etc.) 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 connector input, and many have RCA connector 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.
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 (below).
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.
Solo in place (SIP) 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.
For example, if an engineer wishes to control microphones for three background vocalists at one time, muting them or changing their volume relative to a lead singer, they might create a VCA rather than adjusting all three volumes separately. A sub-mix would be useful if they wanted to process all the singers together, adding the same amount of reverb or compression to each; but the VCA allows each channel to retain its distinctive processing while giving the engineer the ability to quickly adjust the group's volume or mute them.
In a typical live sound mixing context, with a band playing at a venue, consisting of a rhythm section, solo instrumentalists and singers, the master control section allows the audio engineer to control the volume of the entire group with just one fader (for monaural mixers) or a pair of left and right faders (for stereo mixers).
Subgroup and main output fader controls are often found together on the right-hand side of the mixer or, on larger consoles, in a center section flanked by banks of input channels. Matrix routing is often contained in this master section, as are headphone and local loudspeaker monitoring controls. Talkback controls allow conversation with the artist through their monitors, headphones or in-ear monitor. A test tone generator might be located in the master output section. Aux returns such as those signals returning from external processors are often in the master section.
There are usually one or more VU meter or to indicate the levels for each channel, for the master outputs and to indicate whether the console levels are clipping the signal. The sound engineer typically adjusts the gain of the input signals to get the strongest signal that can be obtained without causing clipping. Having the gain set as high as possible improves the signal-to-noise ratio. Most mixers have at least one additional output besides the main mix. These are either individual bus outputs or auxiliary outputs, used, for instance, to output a different mix to onstage monitors.
The meters may be above the input and master sections or they may be integrated into the input and master sections themselves. Meters may have needles or . On meters using LEDs, there may be different colored LEDs to indicate when there is signal present in the channel's input; the audio level of the channel, typically by lighting up more LEDs; and clipping, which may be indicated using a different colored LED. In one popular color-coding system, green LEDs indicate signal presence and the audio level; one or more amber LEDs indicate that the channel is approaching clipping; and one or more red LEDs indicate clipping.
As the human ear experiences audio level in a fashion, mixing console controls and displays are almost always labeled in , a logarithmic measurement system. Since the decibel represents a relative measurement, and not a unit itself, the meters must be referenced to a nominal level. Most professional audio equipment is referenced to a nominal level of +4 dBu, while semi-professional and domestic equipment is usually referenced to a nominal level of −10 dBV.
Some mixers can
Every analog to digital conversion and digital to analog conversion within a digital mixer introduces latency. Audio inserts to favorite external analog processors make for approximately double the usual latency. Further latency can be traced to Data conversion such as from ADAT to AES3 and from normal digital signal processing steps.
Within a digital mixer, there can be differing amounts of latency, depending on the routing and on how much DSP is in use. Assigning a signal to two parallel paths with significantly different processing on each path can result in when recombined. Some digital mixers incorporate internal methods of latency correction so that such problems are avoided.
Most digital mixers use technology to reduce physical space requirements, entailing compromises in user interface such as a single shared channel adjustment area that is selectable for only one channel at a time. Additionally, most digital mixers have virtual pages or layers that change fader banks into separate controls for additional inputs or for adjusting equalization or aux send levels. This layering can be confusing for some operators. Many digital mixers allow internal reassignment of inputs so that convenient groupings of inputs appear near each other in the fader bank, a feature that can be disorienting for persons having to make a hardware patch change.
On the other hand, many digital mixers allow for extremely easy building of a mix from saved data. USB flash drives and other storage methods are employed to bring past performance data to a new venue in a highly portable manner. At the new venue, the traveling mix engineer simply plugs the collected data into the venue's digital mixer and quickly makes small adjustments to the local input and output patch layout, allowing for full show readiness in very short order. Some digital mixers allow offline editing of the mix, a feature that lets the traveling technician use a laptop to make anticipated changes to the show, shortening the time it takes to prepare the sound system for the artist.
In a digital mixer, the microphone preamplifier is followed by an analog-to-digital converter. Ideally, this process is carefully engineered to deal gracefully with overloading and clipping while delivering an accurate digital stream. Overloading during further processing and mixing of digital streams can be avoided by using floating-point arithmetic. Intermediate processing in older systems using fixed-point arithmetic and final output in all digital systems must be controlled to avoid saturation.
Analog mixers, too, must deal gracefully with overloading and clipping at the microphone preamplifier and as well as avoiding overloading of mix buses. Noise is present at all stages of an analog mixer, though good gain stage management and turning unused channels down to zero minimizes its audibility. Digital circuitry is generally more resistant to outside interference from radio transmitters such as walkie-talkies and cell phones.
Many electronic design elements combine to affect perceived sound quality, making the global "analog mixer vs. digital mixer" question difficult to answer. Experienced live sound professionals agree that the selection and quality of the microphones and loudspeakers (with their innate higher potential for creating distortion) are a much greater source of coloration of sound than the choice of mixer. The mixing style and experience of the person mixing may be more important than the make and model of audio console. Analog and digital mixers both have been associated with high-quality concert performances and studio recordings.
Most rock and pop bands use a mixing console to combine musical instruments and vocals so that the mix can be amplified through a nightclub's PA system. Among the highest quality bootleg recordings of live performances are so-called soundboard recordings sourced directly from the mixing console.
Radio broadcasts use a mixing desk to select audio from different sources, such as CD players, telephones, remote feeds, prerecorded advertisements, and in-studio live bands. These consoles, often referred to as air-boards are apt to have many fewer controls than mixers designed for live or studio production mixing, dropping pan/balance, EQ, and multi-bus monitoring/aux feed knobs in favor of cue and output bus selectors, since, in a radio studio, nearly all sources are prerecorded or pre-adjusted.
DJs playing music at a dance club use a small DJ mixer to make smooth transitions between songs that are played from sources that are plugged into the mixer. Compared with other mixers that are used in sound recording and live sound, DJ mixers have far fewer inputs. The most basic DJ mixers have only two inputs, though some have four or more inputs for DJs using a larger number of sources. These sources could include turntables, CD players, portable media players, or electronic instruments such as or . The DJ mixer also allows the DJ to use headphones to cue the next song to the desired starting point before playing it.
Hip hop music DJs and Dub music producers and engineers were early users of the mixing board as a musical instrument. In the 1970s, hip-hop DJs developed a technique of adjusting the fader and crossfader controls of mixers at the same time as they manipulated records on turntables, creating unique rhythmic scratching effects.
Noise music musicians may create feedback loops within mixers, creating an instrument known as a no-input mixer. The tones generated from a no-input mixer are created by connecting an output of the mixer into an input channel and manipulating the pitch with the mixer's dials.
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