A mixer (English Mixing Console , also briefly blender or Console ) serves to combine different electrical signals (audio, video) and is found mainly in the fields of event technology and music production .
A mixing desk for video editing is commonly called an editing desk , but mostly a video mixer . The the lighting of stages used lighting control systems are colloquially often called Lichtmischpult referred, although in this case, no signals are mixed. The term mixer is mainly used in connection with sound engineering .
An audio mixer - also known as a sound mixer , audio desk , mixer , mixer or console - is used to transfer electrical sound signals from various sources (e.g. microphones , playback devices or electronic sound generators) to two or more output sums or buses (sub-sums several signals), mostly after frequency response and dynamic changes. For stereophonic mixes , for example, all signals present at the mixer are merged on the stereo channels "Left" and "Right". Multi-channel surround mixes can also be created with suitable mixing consoles. There are different mixing consoles for the respective sound engineering applications, such as recording and mixing in recording studios , live sound reinforcement , DJ or broadcasting, which can vary greatly in terms of size, functionality, ergonomics, sound properties and price from 50 euros to over a million euros . Audio mixing consoles are available as analog mixers, digital mixers and powered mixers.
In most cases, a mixer is divided into various functional areas. In the usual configuration, the signal paths mostly follow the reading direction from top to bottom and from left to right.
The first section is made up of several audio inputs. If necessary, these are further grouped according to mono and stereo inputs.
On larger mixing consoles, there are subgroups with which several input signals can be combined, for example to be able to control their volume at the same time, to send them to different tracks of a recording device or to a separate PA group (sound reinforcement group). For mixers that are used for DJing, a crossfader is also common between the subgroups.
Return channels / effects
The signals branched off from the individual channels to internal or external effects devices can be mixed back into the sum signal, sometimes also into certain subgroups.
Master / sum
The final mix is finally fed via a master fader to a PA, recording device or transmitter - external or integrated in the power mixer .
The operator can select various points in the signal path, usually marked with a "Solo" switch / button, in order to reproduce or preview them on headphones or loudspeakers in the control room .
There are analog, digital and hybrid (analog and digital technology combined) mixing consoles. In analog mixing consoles, the signal is always an electrical copy of the sound and is processed that way. In digital mixing consoles, on the other hand, the sound is converted into a digital signal and processed by processors ( DSP ). Hybrid consoles have digital control and analog signal processing.
All of these techniques have their advantages and disadvantages. In this way, a small mixer can be manufactured more cheaply using analog technology, since less circuitry is required. As the number of channel strips and outputs increases, so does the circuit complexity and thus the price. Large mixing consoles can usually be produced more cost-effectively using digital technology, because basic equipment is more expensive, but expansion and division is cheaper because the digital signals are transmitted on a common data bus and not by separate electrical conductor tracks. In addition, the number of control elements can be saved with digital consoles, since a controller or a button can be assigned different functions. Control elements no longer have to be available for all channels. The existing channel control strips can be used multiple times by switching layers or banks. In this way, numbers of channels are possible that would no longer be possible with an analog design for reasons of space. With today's digital consoles, most of the settings (fader positions, channel on / off switches, sound and panorama settings, etc.) can be saved in so-called scenes or snapshots and called up again in fractions of a second if necessary. Effect devices such as compressors are often already integrated in digital consoles. This saves space and costs for additional devices compared to analog technology.
Furthermore, some digital models can also save dynamic control processes such as fader movements and run them automatically ( dynamic automation ). Hybrid consoles also offer this option for analog signal processing. However, the circuit complexity and thus the price for the coupling of the digital control with the analog signal processing is very high compared to a purely digital approach and is therefore hardly used today. Only digital level control in otherwise analog consoles is still in use. Real hybrid consoles such as the Euphonix CS series or the Lawo PTR are no longer produced today.
Mixing consoles can also be implemented on a computer. They are mostly integrated into so-called digital audio workstations (DAW).
The most important features of a mixer are the number of input channels, the number of output buses, the sound processing options and the ergonomic arrangement of the controls for the respective application. On the purely technical side, the decisive feature is the signal quality. The frequency response should be as linear as possible, and the dynamic range , i.e. the distance between the inherent noise of the mixer and its distortion limit, should be as large as possible.
Typical signal flow in the audio mixer
At the beginning of the signal path in a sound mixer, the signal source is connected to either a line or a microphone input, depending on the level. Line inputs are used to connect comparatively high-level audio devices such as keyboards and CD players and are usually available in the form of jack sockets , or cinch for simple devices . Microphone inputs, on the other hand, are usually in the form of XLR sockets and often have phantom power for the use of high-quality condenser microphones . A rotary control (input amplification, gain) is used to adjust the input level of the signal source to the optimal working range of the mixer. A special microphone or equalization preamplifier for turntables can also be installed here. Either a peak meter or a vu meter is often available for visual control of each channel level . In addition to the gain control, there is usually a pad switch (attenuation switch) with which an input signal that is too loud can be reduced by a certain amount (usually 20 dB).
Many mixing consoles also have a so-called low-cut filter (a high-pass filter that cuts off disruptive low frequencies, e.g. caused by steps on the stage or gripping movements on the microphone). The cut-off frequency of this filter can often be set, either with a two-stage button (to switch between e.g. 80 Hz and 160 Hz), or even with a rotary potentiometer .
If it is a digital mixer, the analog / digital conversion of the signal follows at this point.
Mixers with more sophisticated equipment then have a phase switch with which the direction of oscillation of the signal can be rotated by 180 ° (wave crest becomes wave trough and vice versa). This is useful either to correct polarity errors in the cabling or to adapt signals of opposite polarity due to multiple microphones of a sound source (e.g. when miking the snare of a drum kit from above and below).
Next, the signal goes through the tone control (filter, equalizer ). The sound of a signal can be processed in different frequency bands (e.g. bass, lower middle, upper middle, treble). The level of these bands can be increased or decreased. If the mixer also has a frequency controller, the individual bands can be shifted if necessary, which enables more targeted adjustments to the frequencies actually occurring in the signal. If there is also a quality controller (also labeled Q), the width of the influence on a strip can be varied. If all of the control options mentioned are available, one speaks of a fully parametric equalizer. In addition, separate, very steep high-pass and low-pass filters can also be present for the bass and treble ranges, which allow all frequencies above or below a certain cut-off frequency to be completely filtered out.
With some consoles, the dynamics of the signal can be influenced by means of a noise gate and / or a compressor (switchable before or after the EQ) . Certain mixers have further by so-called insert jacks in the input sections of the channels that the grinding allow external dynamic or effect devices in the respective channel.
The further course of the channel strip is followed by the on / off switch ( On / Off, Mute ) and, as an elementary component, the slider for the channel level, usually known as a fader, which is available on every mixer , and is also designed as a rotary potentiometer on compact mixers .
In the signal path behind the fader follows the panorama control (also called panpot , contrary to the logic on the control panel above the fader), which can be used to determine how the signal is positioned in the stereo image of the mixer. It is a fader (similar to a crossfader ) and is used to distribute a signal after the channel fader to the right and left channels in the stereo mix; If the channel is assigned to a subgroup, the signal is routed there accordingly, with the right control position corresponding to the even-numbered subgroup, the left to the odd. In order to achieve a loudness that remains the same overall, the signal is attenuated to a greater extent on the side facing away from the controller, following a corresponding curve, and less on the side facing the controller. With the usual intensity stereophony in mixing consoles , no signals are changed in their transit time or sent to the opposite channel.
The last link in the channel strip is the so-called routing. If the mixer has subgroups, the signal can be sent to the master signal via switches next to the fader, either as an alternative or at the same time as the master signal. Likewise - especially with digital mixers - each individual input channel can be assigned directly to a track of a multi-channel recorder.
The signal of a channel can at various points in the strip and to so-called effect or monitor paths ( Auxiliary -way be sent = auxiliary routes). Usually such aux busses are between “ pre-fader ” (signal is branched after the filter section, before the channel fader, so it is independent of its position) and “ after ” or “ post fader ” (signal depends on the channel -Fader) switchable. The controls for this can usually be found on the control panel directly above the panpot.
Mixing the signals
Mixing several signals is a technical challenge because the volume of one channel must not affect the volume of another. If you just connect the middle slider of all volume or panorama potentiometers with each other, the output impedance of a channel influences the load impedance that affects the other channels, and in extreme cases it can short-circuit the other outputs when one channel is completely "turned off" and its possible Panorama plate is in an extreme position (see also overlay set ). To avoid this, make sure that all channels have a fixed output impedance. In simple passive mixing consoles (i.e. without their own voltage source) this is done through a resistor in the order of magnitude of the potentiometer resistor at the output of each channel. Since this resistance represents an additive constant in the function of the output resistance of the potentiometer position, the influence of the potentiometer position on the output resistance of a channel is reduced. In active mixing consoles, each channel is followed by an impedance converter, i.e. an operational amplifier or a transistor / triode in a collector circuit / drain circuit / anode circuit with a defined output impedance. This means that the impedances during mixing are completely independent of the output impedances of the channels. With many channels, it should be noted that the mixed voltage - resulting from the superposition theorem - corresponds to the average voltage, i.e. the amplitude of an input is divided by the number of channels. It must therefore be amplified by the number of channels to actually get the sum of the voltages.
The master section of the console follows the routing, in which the signals are mixed and the sum is output to one or more master outputs. Separate outputs for recording the PA composite signal are usually referred to as two-track , abbreviated 2TK (-out); a 2TK in path is used to play back the recorded signal directly without any further influence.
Larger mixing consoles also have subgroups on which several input signals are mixed. Sound sources such as drums, choir or orchestral voices can be combined and faded into the master signal with a single fader. The individual tracks of a recording device or various loudspeaker systems can also be recorded. Mixing consoles for music performance have a similar construction with the horizontally built-in crossfader ; Here, one or more inputs are assigned to the left and right sides, between which a single controller can be used to fade.
During a production, the operator at the desk needs not only the master signal but also the possibility of pre-listening to individual channels or subgroups in the control room or on headphones without influencing the output signal. With the pre-fader listening (English pre fader = before the volume control) can (especially for live production) a new source inspected are as applied on the output of other channels. For this purpose, each monitoring point has its own PFL switch, which when activated, the console monitoring only displays the individual PFL-switched signals. Similarly, the mixdown solo mode (AFL, after fader listen = listening behind the fader) allows you to listen to individual channels exactly as they sound in the mix, including their level and panorama settings and the effects applied to them. This is also useful for troubleshooting or for readjusting filters during ongoing production and for assessing material that has just been recorded, the "rear belt control".
It is also important to give those involved a feedback, the so-called monitoring . If no headphones or in-ear monitoring systems are used on which the master signal can run without causing feedback into the pickups, special mixes must be created for this. In the simplest case, this can be done via the aux paths, but larger mixing consoles have special options for creating headphone and monitor mixes and distributing them to the recording rooms and people involved. A separate desk is used on the stage for large live performances.
Some consoles also offer the possibility of communication between the sound engineer and the people in the recording room (talkback).
Professional mixing consoles for permanent installation in large studios usually no longer have separate input and output connections. Rather, the cabling is done using multipin connectors. This means that many analog audio paths can be efficiently and clearly laid out using multicore cables, for example in different studio rooms or from the FOH to the stage, where the individual connections are on stage boxes .
A patch panel (engl. Patchbay ) installed in the control panel or in an external rack on the internal inputs and outputs of all audio devices present in the studio are connected, allowing all devices very light and flexible short simply by plugging in cables together to connect ("patch").
Mixing console concepts
With this concept, only one signal can be processed with one channel, that is, the rear tape control can only take place via another dedicated channel. The number of subgroups is fixed and cannot be expanded at will. This is why this mixer concept is mostly used today in the live area as an FOH mixer. Before the advent of inline mixing consoles, split consoles were also common in studios; for this purpose, large split consoles had their own monitoring section with a corresponding number of channels. One advantage of the concept is the better overview of the signal flow, the disadvantage is the lack of flexibility and, especially with larger setups, the enormous space requirement.
The first mixer with the inline concept was developed by the company SSL and is still the professional standard in large music studios today. The idea behind this concept is that one channel can process two signals at the same time. On the one hand, the input signal of the source to be recorded is applied to the main fader and is sent to the tape recorder or the DAW. At the same time, the “small” fader in the same channel strip can be used to monitor the off-tape (back-tape) signal. For mixing, the assignment of the faders can be changed, additional signal sources can be imported, channels can be defined as subgroups and the filters and output paths can be flexibly divided between the existing signals of the same channel strip. An additional advantage is the enormous space savings. The inline concept is also known as the "sandwich construction".
The concept of the splint consoles is a mixture of the two previous mixer concepts. The number of subgroups is limited as with the split console, but two different signals can be applied to each channel, one of which is controlled via the main fader, the other via the “ small fader ”, usually a small fader or a potentiometer . The signals can be flexibly switched to the equalizer or the output channels via status switches between the main fader and the "small" fader, depending on the console's equipment. One of the best-known consoles of this type is the "8-Bus" console from Mackie .
- Line mixer: This mixer concept usually does not have microphone inputs and is often used by keyboard players on stage for a pre-mix.
- Monitor consoles: These mixing consoles are used in the live area and are used for the monitor mix on stage. Therefore they have a large number of aux paths.
For special purposes, mixing consoles are equipped with additional functions that simplify work processes either via their own control elements or via the connection with existing functions.
The condenser microphones that are primarily used in the studio require an operating voltage. This can be switched on as phantom power in most mixing consoles . If a mixer has no phantom power, it is possible to connect a power supply or a suitable preamplifier between the microphone and the mixer. The voltage is usually 48 volts .
Fader / hotstart
Especially with broadcast mixers and sometimes also with DJ mixers, the playback device connected to this channel can be started by pulling up a channel fader (fader start) or pressing the signal (on) switch (hot start).
To avoid feedback, its signal must not be reproduced in a studio room in which a microphone is in operation. The muting can be configured in such a way that when a microphone channel is opened, the monitor boxes in the corresponding room are switched off and the signal is only available via headphones.
In particular, digital mixing consoles can be equipped with a more or less complex effects section ( see also: Channel strip ). This ranges from simple sum effects (e.g. simple reverb , flanger or chorus ) in devices in the lower price segment to high-quality effects and dynamics processing devices for each channel strip in expensive consoles.
In addition to the filter options in the individual channel strips, the output signal can be adapted to the conditions of the room and the loudspeakers with a master equalizer . Similar to the integrated effects, these equalizers hardly meet professional standards in cheap devices, and because of the limited space available on the control panel, only a few, and therefore relatively wide, filter bands can be offered.
A power mixer combines a (mostly somewhat simpler) mixer and an audio frequency power amplifier in one device. Devices of this type are mainly used for live performances in front of a somewhat smaller audience of around 50 to 100 people, for example by music combos, dance groups, for karaoke events, by showmen and advertising organizers. As part of a public address system, they keep the overall effort low , since otherwise only the loudspeaker boxes and the sound sources are essentially required.
Power mixers are offered by various manufacturers and usually have the usual desk shape. In terms of their mode of operation, they basically also belong to the group of audio amplifiers and are often built in stereo technology, i.e. two-channel. Simpler devices, mostly not in the form of a desk and operated from the front panel, which rarely have two channels, are generally referred to as “mixer amplifiers”, but in the lower price segment also as “powered mixers”. The definitions cannot therefore be precisely delimited.
In networked production systems such as ARD radio, many mixing consoles in the studios can be remote controlled. The controllers of the actual desk are moved by servo or linear motors . This means that the position of the controller remains "current" and manual intervention on site is still possible. Typical remote control applications are:
- Remote interviews where only the interviewee sits in the local studio (no local technician present)
- complex live broadcasts from several studios that are “driven” by a central control room
- Programs with computer-controlled processes (typically at night), in which a computer operates the mixer and only one person is present (which private broadcasters sometimes even do without)
- “Running” physical sound carriers (e.g. tapes) on decentralized machines (example: a live broadcast is produced at HR in Frankfurt, a contribution is supplied by the Kassel studio and is available there on tape). However, this application is disappearing with the spread of server-based audio data storage.
Well-known mixer manufacturers
- Allen & Heath
- AMS Neve
- DHD audio
- Solid State Logic
- Stage Tec
- QSC Audio
- Studer ( Harman International Industries )
- Rolf Beckmann: Manual of PA technology. Basics, components, practice. 10th edition. Elektor, Aachen 2001, ISBN 3-921608-66-X .
- Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr: Manual of the recording studio technology. 2 volumes. Published by the ARD.ZDF media academy. 7th, completely revised and expanded edition. Saur, Munich 2008, ISBN 978-3-598-11765-7 .
- Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
- Hubert Henle: The recording studio manual. Practical introduction to professional recording technology. 5th, completely revised edition. Carstensen, Munich 2001, ISBN 3-910098-19-3 .
- Basic knowledge: Mixing consoles - structure / functions , sound & recording
- Eberhard Sengpiel: Panorama plate, panorama regulator = panpot. (PDF; 257 kB) In: sengpielaudio.com. Retrieved February 25, 2011 .