The Mixer: Functions & Connections Explained

There comes a time in every musician’s life when they are forced to confront a mixer for the first time. To the un-schooled user, these chunks of equipment can seem intimidating and complex, and while mixers range from the super-compact to the desk-sized gigantic, all of them are based on the same set of principles and will offer the same basic set of functions and connection options. In this blog, we offer a step-by-step explanation of the ins and outs of mixers.

The Principles of a Mixer

In basic terms, a mixer is a piece of equipment that takes multiple audio signals and blends them together into one mono or stereo signal. This mixed signal is then sent out via the ‘main output’ to gear like a PA amplifier or a set of active speakers. Using the buttons and faders that any mixer control panel offers, all of the different audio sources can be balanced and mixed until they sound like a cohesive whole. This is the principle on which mixers have been founded from the very beginning, and while things like equalisers, effect sends, and sub-groups were added during the sixties and seventies, not that much has changed. Used for live sound as well as for recording, the original mixers were always based on analogue technology, and while digital mixers are just as common now, some engineers still swear by the warmer sound of a genuine analogue mixer. Since they’ve been developing for way longer than digital models, there’s also a far wider array of analogue mixers available. When looking at the model names of mixers, you’ll usually see a set of numbers that can give you a hint as to what features are on offer. A combination like 4-2 means four inputs and two outputs (which combine for a stereo output). If you see a combo of three numbers, then the number in the middle indicates the number of available sub-groups. If the model name includes ‘FX’, this lets you know you’re looking at a mixer that comes with built-in effects, like reverb.

The Mixer: Functions & Connections Explained
A mixer with built-in effects. Here, you can see two effects sections, meaning that a maximum of two effects can be used at the same time.

The Channels & Channel Strips

The channels are usually lined up on the left of the control panel. Each channel is made up of an input (mono or stereo) and a number of controls that are dedicated to that particular channel. You can get really small mixers that have just two channels like this, and the next step up would usually be a mixer with four channels, and then a multiple of four after that – so 8 channels, 12 channels, 16 channels, and so on. The channels of most mixers tend to include the same set of controls, but there are some differences here and there. For example, the microphone channels will often have a different layout than line signal channels, but whatever the input type, the channel input combined with its set of dedicated controls is always referred to as a channel strip. Channel strips can even be picked up separately – most of the time, these are high-spec, high-end strips with prices to match.

The Mixer: Functions & Connections Explained
The channel strips of this mixer include controls like channel faders, PFL (pre-fader-listen) buttons, and the option to create two sub-groups via the ‘1-2’ and ‘3-4’ buttons.

Channels: More is Actually More

One of the first questions you need to ask yourself when thinking about buying a mixer is “How many channels do I need?” and the answer, of course, depends on the size of the band or ensemble that you’re planning to mix. The golden rule here is that it’s always better to have too many channels than not enough. For example, even a band with a standard setup can quickly eat up 16 channels, and you might also find yourself sound-checking a couple of bands ahead of the gig and want to be able to leave settings as they are. With a digital mixer this is largely solved by presets, but since bands can always come in with their own microphones or even more instruments, having the right number of physical channels is the most important feature to consider. Try not to get blinded by the numbers though. Some mixers only offer a limited number of preamps compared to the total number of inputs, leaving you with a bunch of leftover line-inputs that don’t have preamps. If you want to mix in maximum comfort, then a minimum of twenty-four channels is recommended.

Channel Controls

Each channel will always come equipped with a sliding fader for controlling the channel volume. Smaller mixers sometimes have rotary knobs instead of faders, but to keep things simple, we’ll just refer to the volume control as the fader. By setting the channel faders, you’re determining the signal level of the channels as they are sent as a mix to the output. Usually, channel strips have two or three controls for equalising. These adjust the high, middle, and low frequencies of the audio signal being sent through that particular channel, so you can do things like add more bass or remove the trebles. You’re also likely to see a knob marked PAN or BAL (balance), which is used to move a mono signal over to the left or right of the stereo image. The mute button silences the channel, and with some models, the signal is then automatically sent to a different output that can then be used as a sub-group.

The Mixer: Functions & Connections Explained
Each channel of this mixer has a separate compression control knob and a set of three knobs to control a three-band equaliser.

Using the Equaliser

With most mixer control panels, the EQ knobs for each channel are lined up underneath the channel gain knob. Generally, equaliser controls are only used to cut or boost specific frequencies. DJ mixers or cheaper PA mixers often have just three EQ controls for the low, middle and high frequencies. More extensive mixers like the Behringer Eurodesk offer a parametric EQ section for the mid-range frequencies. A parametric equaliser is made up of two control knobs: one to select a specific frequency range (referred to as a ‘sweep’) and one to determine the cut or boost level applied to the selected frequency range. More expensive models are fully parametric and therefore, every frequency band includes a ‘sweep’. Take another step up and you’ll come across models like those included in the Soundcraft MH Series which include a third control knob for adjusting the ‘Q’. This means that rather than just being able to select the frequency range that’s cut or boosted, you can influence the extent to which the surrounding frequencies are adjusted. When boosting a frequency, a lower Q value is set to ensure a more natural sound. When cutting a frequency, it’s best to keep the margin as small as possible so that you’re removing as little of the unwanted frequencies as possible. Many mixers also offer an EQ section for the master signal. These are usually small faders for adjusting anywhere between three and thirty-three frequency bands, and are used to adjust the total sound which can be useful for boosting or tempering any troublesome frequencies or to counter the adverse effects of bad acoustics in the performance or recording space. This EQ section is usually pretty limited and is by no means a good replacement for two external thirty-three band equalizer since they offer far more in-depth tools for adjusting the left and right stereo signals, making it match up with the performance space.

The Inputs

Most mixers will come equipped with at least a small army of different inputs. The mono channels usually have two inputs: a microphone input (XLR) and a line input (6.3mm jack) that can be used one at a time, and you can also get mono channels that have just a line-input or microphone input. Many mixers will also have stereo line-inputs, with a pair of jack ports: one for the left and one for the right stereo channel. Other possible inputs include ‘Aux returns’ and ‘2-Track’ inputs (and 2-Track outputs) designed for connecting a CD player or other audio playback gear or recording equipment. We’ll go into more detail about Aux return ports later in this blog.

The Mixer: Functions & Connections Explained
A mixer with mic/line combo inputs and insert ports

Line, Mic & Gain/Trim

Since a microphone signal is weaker than the line signal of something like a keyboard, the signals of any connected microphones need to be run through a preamp so they can be raised to the same level as a line-signal. This is because mixers are generally designed to work with line-level audio signals, and as such, each microphone channel is given its own preamp, the level and influence of which is controlled using the Gain or Trim knob that’s usually fitted at the top of the channel strip. When set to ‘0’ or ‘U’ (Unity), the signal is neither strengthened or weakened. Usefully, some channels are also fitted with a small LED light that will blink when the signal is too strong, so you can reduce the preamp gain/trim and avoid distortion. If you’re connecting a line-signal to a preamp-fitted channel, then you will barely need to raise the gain, if at all. Correctly setting the gain, especially when it comes to microphone signals, must be precise. If it’s not right, then you’ll have trouble adjusting the sound. The fact is that there’s very little room to play with when tweaking input gain, so it’s a good idea to take a look at the user manual of your mixer since they often give you a good indication of how best to set the gain.

The Mixer: Functions & Connections Explained
A mixer with gain controls, individual phantom power switches, 26dB buttons to switch between mic and line, and low-cut filters

The Sonic Colouring of Preamps

The first step in the signal path of a mixer is the point where the instrument is connected, so either a microphone or line input. A microphone has a lower output volume than a line level signal, which is another reason why microphone inputs are always fitted with gain-boosting preamps as standard, to strengthen the signal, and as we’ve already covered, the level of ‘boost’ is controlled using the gain/trim knob that’s usually found at the top of the channel strip. But preamps don’t simply raise the volume of the input signal, they actually make a significant difference to the quality of sound. This is determined by the character of a particular preamp, and how it colours the signal. Mixers made by brands like Mackie and Behringer are known for preamps that add relatively little colour to the sound, while Soundcraft and A&H preamps are known for adding warmth. When it comes to expensive and budget-priced models, the difference is often negligible, and the sound difference will be far more noticeable in the studio than it would be in a live setting. If you really want to profit from the depth and added dimension that a preamp can offer, then you’re better off looking at the more expensive end of the spectrum. There are actually many sound engineers that often use one or two external preamps to guarantee that they’ll get a specific sound out of the vocals, guitars, or drums.

Phantom Power

Unlike dynamic microphones, condenser microphones require 48 Volts of power in order to function. This is known as phantom power and can usually be fed to the microphone by your mixer by simply connecting it to the XLR port and activating the phantom power function using the on/off switch. Sometimes, this is a phantom power switch for the whole mixer, or you get a phantom power switch per microphone channel. In principle, phantom power doesn’t cause any harm to dynamic microphones, but just to be sure, it’s always recommended to switch the phantom power off when no condenser microphones are connected to your mixer. It’s also a good idea to switch off the phantom power before plugging in or unplugging anything, since it can cause a loud bang.

-10dBv & +4dBu

There are two standards for the level of a line signal: -10 dBv and +4 dBu.

  • Professional studio equipment almost always operates using the higher level of +4dBu.
  • Hi-fi equipment and instruments like keyboards use a lower level of -10dBv.

With many mixers, you’ll find a -10 dBv and +4 dBu selector switch, which can be found fitted to the inputs as well as the outputs. Say you connect a portable recorder (-10dB) to an output that’s been set to +4dBu – the signal is probably going to get too loud too easily and leave you with distorted sound. By switching the output to -10dBv, the problem is immediately solved.

Balanced & Unbalanced

The microphone inputs (XLR) are usually balanced to counter any microphone signal interference. In this dedicated blog, we dive deeper into the difference between balanced and unbalanced signals, but all you need to know here is that the better the mixer, the more likely it is that every input and output is balanced – including the line signals. In the case of balanced jack ports, a stereo jack cable needs to be used since, while a mono jack can be plugged in without any issues, you’’ll miss out on the benefits of having a balanced input or output. Normally, inputs and outputs are marked BAL or UNBAL so you know exactly what kind of port you’re using.

Microphones & Voltage

When a line output is taken from a stage piano and connected to a microphone preamp, a massive amount of gain is generated and you’ll get nothing but distorted noise. On top of that, line signals are usually unbalanced, meaning that when bridging longer distances with longer cables (from about five-metres up), the more sensitive the signal will get to noise and interference caused by electro-magnetic radiation. In this case, a DI box can also be used to weaken the high voltage of the line signal as well as balancing the signal and sending it as a microphone level to a mixer. Active DI boxes and condenser microphones have no voltage at all. These are fed phantom power (usually at 48 Volts) by the mixer via the connected XLR cable. Cheaper PA mixers often have a single phantom power switch rather than a switch per channel, which isn’t the best when, for example, you want to use a ribbon microphone or other equipment that’s more sensitive to electric current. In those cases, it’s better to seek out a mixer fitted with a phantom power switch per channel – and once you find one, always remember to only use the phantom power on/off switch when the channel is muted or make sure that the gain is all the way down, otherwise you’ll hear an electronic click or pop which, at a louder volume can damage both the ears of your audience and your speakers.


Next to microphone inputs you can sometimes find what’s referred to as a low-cut button (or high-pass, or rumble). This button activates a filter that pushes back the lower frequencies. The filter frequency normally sits between 60Hz and 80Hz, so you can literally filter out the bassy sounds of things like footsteps and passing traffic, removing it before it reaches the preamp. Due to the nature of the low-cut filter, it’s not designed for the sound of a kick drum or bass guitar since it’ll remove all the ‘meat’ from the sound.

Insert (for Serial Effects)

The channels of a mixer could come equipped with inserts, so that the signal of a specific channel can be detoured through an effects unit before being sent back through the channel. To do this, a cable with one stereo jack at one end and two mono jacks at the other needs to be used. The stereo jack is plugged into the insert, while the two mono jacks are plugged into the input and output of the effects unit, creating a detour through the effect. This method should only be used when working with effects that lend themselves to insert effects (serial effects), since when sent through the insert, the whole signal is sent to the effects unit (a compressor, for example) and the treated signal then replaces the original signal.

Aux Send & Return (for Parallel Effect or Monitoring)

The aux send and aux return are used to add parallel effects to the sound. Via the aux send, the signal is tapped off, sent through an effects unit and then added back to the original signal via the aux return (mono or stereo). An effect like reverb is a typical parallel effect and is therefore always looped through the aux send and return. Each channel has a control knob for setting how much of the signal is fed through the aux send, which can be set to ‘0’ if a specific channel doesn’t need to be treated with the parallel effect. Some mixers also have a control knob for adjusting the overall volume of all of the aux sends, and for the aux return, there’ll always be a knob for controlling the level of the processed signal coming back through. The aux send can also be used for connecting up a monitor. In this case, every aux knob on every channel will be used to determine the level of each channel as it’s sent to the connected monitor. The aux return, meanwhile, can also be set up as an extra stereo or mono line input, but if you use it as a line input, you only have control over the volume level and will have no way to influence details like the EQ.

The Mixer: Functions & Connections Explained
This mixer has two aux sends and two built-in effects sections (FX). Per channel, you can determine the signal level fed through the different aux sends and effects. You can also see the pan knobs which determine how far left or right a channel is placed in the stereo image.

More About Auxes & Effects

The auxes, or ‘auxiliary sends’ always have a fixed place under the EQ section. With an auxiliary send, it’s possible to independently send each track to a separate output. This output can lead to an effects unit or a monitor, and the ‘return’ can either come in the form of a rotary knob or a separate fader that determines how much of the processed signal is mixed with the original signal. This way, all of the channels of the mix can (for example) be run through the same reverb effect. This isn’t just space and money saving, but ensures a more coherent mix. As such, it’s really important when picking out a mixer to take the rest of your setup into account, so that you’re certain that you have enough auxes to play with. When you’re working with a separate monitor desk, then you’ll have more than enough with just two sends, which can be used to add gear like an external reverb and delay. But there are many companies that offer analogue mixing desks with a digital effects processor, like Yamaha, Mackie and Behringer. By using built-in effects, you can use the front-of-house mixing desk to control the monitors, and the number of auxes needed then depends on the number of monitor mixes you need. An internal effects processor can be a useful solution when either space or money is limited, but the downside is that they can be far less convenient than external effects gear, especially since you rarely get the power to adjust any of the effect parameters. What you often get instead is an immense list of presets that are navigated by an unclear overview, which is not always the most intuitive way of working. The reverbs can often sound a little ‘cheap’ and electronic and the delays don’t usually come with an adjustable speed or tap tempo. If you’re setting up your mixer in the rehearsal room, some built-in effects will definitely do wonders for the vocals, but if you’re engineering for live bands, you’ll probably be better off using some external effects made by well known developers like TC Electronic or Lexicon.

Pre & Post Fader

An aux send can be tapped before or after the fader (so the channel volume control). When set to ‘pre’, it’s tapped before the fader, and when set to ‘post’, it’s tapped after the fader. When the signal is post-fader, then the processed signal (e.g. reverb) always maintains the same proportion as the original signal and therefore is affected by the fader setting, and usually, this is what you want. When the aux send is pre-fader, then the aux send signal remains constant, no matter the fader setting. The pre setting is great when you need to use the send as a monitor signal. Sometimes, you can set the send to pre or post fader with a button that’s usually placed just next to the aux send rotary knob.

Note: the aux send signal is (in principle) not always placed before the low-cut and equaliser functions of the channel, even though the channel is set to pre-fader.

Sub Groups

Sub groups (also referred to as groups or sub-busses) tend to be offered by larger mixers. Sub groups are extra outputs that allow you to send a selection of one or more channels out, which is useful for making custom monitor mixes for one or more of the musicians on stage. Using the controls included on each channel strip, you can determine which sub-group or groups the channel signal is sent to, while the signal is still sent to the main output.

The Mixer: Functions & Connections Explained
A mixer with volume controls for the main outputs (stereo), two groups for the sends and returns and for the built-in effects

Monitor, Control Room, Solo & Headphones

Besides the stereo main output, mixers will also have a stereo monitor or control room (C/R) output. This output can be connected to gear like an amplifier or active monitors so you can listen to the total mix. The C/R output has its own volume control which ‘goes along with’ the volume of the main output, but not the other way around – so the main output volume is not affected by the C/R volume. A keyboard player, for example, might hook their equipment up to their own mixer and then connect the main output to the PA, and connect the C/R output to their own monitor. Using the C/R volume control they can control their own monitor volume without affecting the volume level sent to the PA. With smaller mixers, the exact same mix is sent through both the main output and the C/R output. With larger mixers, every channel will have a solo button, which is pushed to send the signal through C/R output. This way, you can use the C/R output to isolate and listen to one or more channels without messing with the main output mix. All mixers have a headphone output which is coupled with the C/R output. The mix you hear through your headphone is therefore the same mix being sent through the C/R output, and the headphone volume is controlled by the C/R volume.

AFL & PFL (Solo)

If your mixer has solo buttons for each channel, then usually it’ll also have a switch labelled AFL/PFL. Flick the switch to AFL (after fader listen) and you’ll be able to check the C/R output after the gain, equaliser, and fader settings. So, you’ll hear the solo channels as they are treated – or mixed – before being sent through the main output. As such, the AFL function is great for mixing via the C/R output or headphones. PFL stands for pre fader listen, and when set to PFL, you hear the solo channels before the fader (and after the equaliser), so you can listen to channels even if the fader is set to 0. PFL is designed for checking specific channels in isolation and without the distraction of the rest of the total mix.

Main Out

The main output is what sends the mixed stereo sound from your mixer to equipment like an amplifier and speakers so that the audience can hear it. With smaller mixers, the volume of the main mix is set with a rotary knob. Larger mixers will provide a set of two faders – one for the left side of the stereo image and one for the right. A level meter will also be included (usually a row of colour LEDs) to indicate how loud the main output signal is getting. The top LEDs are always red, and these will light up if the signal is too loud and in danger of distorting. Some larger mixers will also include a dedicated equaliser for the main out so that the final mix can be balanced in greater detail.

A mixer with main outputs (stereo out), aux sends (send), and control room outputs (monitor out)

Routing Options

With larger mixers, you’re able to select one of two different routings – the ‘paths’ along which the different signals travel. The route is selected via a dedicated button, so you can decide whether you want a channel sent to the C/R or headphones, or you can send the signal from an external audio source to the main output so you can play some music between bands. When it comes to routing, the options can differ depending on the mixer, so take a look at the user manual to see what’s possible.


All of the buttons, rotary knobs and faders of a mixing desk are sensitive to dust, moisture, and even smoke. All of these external influences leave deposits on the carbon tracks leading to crackling and volume jumps. The problem can usually be solved by quickly twisting and pushing faders all the way back and forth a few times to shift any built up grub. With faders, you can also use a very small amount of cleaning spray, but the best solution is actually prevention. By keeping your mixer dust free by keeping it covered when not in use and stored in a room with a normal level of humidity, you can extend its lifespan.

Analogue or Digital

The time when analogue gear always sounded warmer than digital gear is long over, which is a real testament to how far digital mixers have come. Digital mixers are also able to offer a mass of benefits when compared to analogue mixers, the first being the size. Digital mixers can be much smaller and space-saving while still offering an array of essential effects – which in analogue terms would easily take up a couple of flight cases. The number of faders can be limited without sacrificing any inputs, and since digital mixers can be fitted with motorised faders, you can work with more banks. This means that as you flip from one bank to the next, the faders will automatically shift into the correct position. With just eight faders, you’re suddenly able to control up to forty-eight channels without having to lug around a two-metre-wide desk. With digital mixers, you can also create and save presets – presets that not only save effects parameters but the entire mixer configuration so it can simply be called up later. It goes without saying that, when it comes to mixing the live sound of two or three bands in one night, this feature is a life-saver. Multiple configurations can be saved, so if you use a mixer for rehearsals, you can strike the perfect balance for band practice and save it just in case a parameter gets accidentally tweaked. Many digital mixers also offer a recording function these days which is not just insanely useful when working on new material in the rehearsal room but for listening back over gigs. Good recordings can even be used as demos, and even album-quality material can be created with just your mixer. There are a number of options available when it comes to mixers that double as digital recorders. Most mixers will record the master mix to an internal memory, an SD card, or USB stick, and sometimes the file is immediately compressed. If you want to make the best quality multi-track recordings then you’ll want to look at mixers that double as audio interfaces, so you can connect it directly to a computer and record the final mix to a DAW.

See Also…

» Analogue Mixers
» Digital Mixers
» Mixers with Built-In Amplifiers
» Rack Mixers
» Mixer Covers & Bags
» Mixer Flight Cases
» All Mixers

» Speakers
» Amplifiers
» Microphones
» PA Starter Sets
» All PA Gear

» Mixer Buyer’s Guide
» How to Clean a Microphone
» Live Stream Your Gig with Great Sound
» Phantom Power: What You Need to Know
» Speakers & Amps: The Difference Between 2, 4, 8 & 16 Ohms
» Buzz, Hum & How to Get Rid of it
» How Many Watts? The Truth About Speakers and Power Output
» Balanced & Unbalanced Connections Explained
» How to Connect a Microphone to a Speaker
» The Difference Between Dynamic & Condenser Microphones
» What’s an Equalizer & What’s it For?
» How to Connect Your Speakers to Your Audio Gear
» The Difference Between Active & Passive Speakers

3 responses
  1. Geoff O'Donnell says:

    Is it better to have the monitor volume slider on the desk higher than the volume control on the powered monitor, or the other way round ie the desk slider down and the monitor volume control higher?

    • Hi Geoff,

      Start with the monitor fader/knob at 0 dB. This is the position at which the fader/knob is almost fully open. The signal can pass through the channel without being attenuated or boosted. Now set the level of your monitor speaker or amp a little higher than you need it to be. This gives you a little extra headroom. Now turn the monitor fader/knob on your mixer down to the desired level. Also make sure to use pre-fader auxiliaries for monitor mixes. This way you can move the channel faders without affecting the monitor mix.

      Marnix | Bax Music

  2. Tynoe says:

    thus useful information

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