What Does A Mixer Do And What Are Its Features?

What does the mixer do? Ever wondered when mixing music? Are you sure you've made the most of it? Let's check them out here.

by Derrick Reeves | Updated: October 11, 2021

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If you’re new to recording, a mixer can be an intimidating piece of audio equipment. They have countless knobs and faders, with different numbers for the left channel and right channel. It looks like there is just too much going on here! 

But it doesn’t have to be that way. A mixer does one thing very well – mixing signals together from various sources into one stereo or multi-channel output signal.  

This means that you can connect multiple instruments (or microphones) to a single input on your recorder, then balance them all out in the mix when recording or playing back. 

The truth is that mixing isn't as complicated as it may seem at first glance. Once you understand the basics, everything else will fall into place.  

Here we explain what each control does, then we take a look at some of the most common features that you might find on today’s mixers! 

What is a mixer?

What is a mixer

A mixer is an electrical device that combines two or more audio signals to make new audio signals. They have a set of input knobs, faders and buttons called channels to control the various sources. Mixers are used to create a mix of these combined sources.  

How does it work? 

The mixer takes a number of input signals from various devices and combines them into the mixer's summing bus or multi-channel output. 

What does summing mean?  

The common mixing practice is called “summing” in which multiple signals are summed together through each channel of the mixer. What you’re doing is taking multiple signals, and blending them all into one stereo output signal. 

There are many different types of mixers, but they all work in the same basic way. 

When you connect an external device (such as a microphone) to your mixer, it sends out a signal on that channel. This is the only source connected to that channel. We’ll call this the 'main' input.  

The mixer receives a signal from the main output, and then this is fed into an equalizer (EQ). This allows you to adjust how much of each frequency band is present in your signal.  

For example, if you want more treble in your signal, you can boost the frequencies at or above 10kHz. What's nice about an equalizer is that you don’t lose any frequencies – it just boosts them (or cuts them) in proportion to how much you have increased (or reduced) their presence. 

The mixer will then send this signal out to a number of channels. Then you can have other devices connected to these channels (called 'auxiliary' inputs).  

You can adjust the volume and tone for each channel separately, so if you want more treble when recording vocals, but less treble when recording an electric guitar or bass, you can easily achieve this. 

Then you need to adjust the overall volume of your mix. This is done on a master channel and can be controlled using either the main volume fader or the pre-fade listen to (PFL) button. What’s nice about this is that you don’t have to change anything in order to hear what you’re doing, you merely press the PFL button. 

Finally, a mixer will have a number of output channels as well. These are used to send your mixed audio to external devices (like speakers or headphones).  

How it works for mixing two sources (e.g., a drum machine and a synthesizer)?  

The drum machine will send an audio signal to channel 1 on the mixer, while channel 2 will be empty. The synthesizer will send an audio signal to channel 2 on the mixer, while channel 1 will be empty. 

The mixer combines these two sources into one stereo signal so you can hear both from your speakers or headphones.  

What happens if there are three or four instruments? What about dozens of them? 

A typical audio mixer has 2-24 channels, allowing you to combine two (or more) sound sources into one stereo signal.  

You can use additional channels if you need to record multiple instruments together for live performances or recording sessions.  

However, once those source signals are recorded, you can no longer switch between them during playback. 

What does each mixer control do?

What does each mixer control do

Here is a brief summary of the various controls you might find on a mixer. 

Channel strips 

A channel strip is an entire section of a mixer that you can control with just one fader. If you want to mix two input devices together, then you can do so easily by using your channel strip’s pan/balance control. 

This greatly simplifies things because it requires only one adjustment rather than the multiple adjustments of two separate channels. What this also means is that you can customize your channel strips to do whatever they’re supposed to be doing (i.e. EQ, mute, fader control). 

If you have a channel strip it will be easier to control everything at once with one handle than twenty individual controls. 


This is where your sound sources are connected. If you’re using a microphone to record vocals, then you need to connect the microphone to an input channel. 

You can also use your input channels for recording instruments, such as kick drums and electric guitars. You may need an audio interface with an input channel called an 'XLR'.  

An XLR is a type of plug that goes into the main audio feed of your mixer. You need to connect your kick drum and electric guitar to something called a preamplifier, which then connects to the XLR input on your mixer.  

What’s nice about this is that you can connect multiple instruments, such as a kick drum and an electric guitar, to the same input channel on your mixer, which allows you to easily control them at one time. 


Inserts let you add devices between the signal coming into a channel and what’s being sent out. What this means is that you can take the input from one device, mix it with output from another device, then send it out to yet another device or back into the mixer as a master track.  

The most typical use of this arrangement is for the microphone when you want to add some effects.  

Just plug your microphone into an insert and then run it through a special effects device (like an echo or reverb).  

What happens in effect is that any sound coming out of the effect will be added to what came in from your mic. The nice thing about this is that you can turn the effect on and off without changing anything else on the mixer (e.g., routing). 

Gain knobs  

On each channel, there is an individual gain control that lets you control the amount of gain for that input signal. This is that it allows you to adjust the volume on a per-input basis.  

What’s also nice about this is that if one input is very quiet, and another loud, you can adjust the gain of the quiet signal while keeping the volume of the loud one fixed. 

Equalizer (EQ) 

There is an equalizer on each channel that allows you to adjust each frequency band. What’s nice about an EQ is that you don’t lose any frequencies, you just boost them (or cut them) in proportion to how much you have increased (or reduced) their presence. 

Auxiliary Send Controls 

These are special controls that affect the level of auxiliary outputs. What they do is allow you to add these channels as buses for other devices (like a group of speakers, or even an external sound recording device).  

Just like with inserts, an auxiliary send control lets you adjust the volume of any signal sent out to these auxiliaries - in addition to the volume of each individual auxiliary.  

You can very easily mix your device into another one using a stereo aux. 

Panning/balance control 

This is a control on the channel that allows you to adjust the balance between two inputs. A pan/balance is that it’s much easier to use and more precise than trying to use two channels (which might be farther apart or share audio input).  

What can also be done with these controls is that you can easily mix two audio signals coming from different devices into one channel. This might be useful for example if you’re using a microphone but want to combine it with your computer sound card.  

If the two inputs are far apart on the mixer, then even at high volumes they will never overlap. What this means is that you can easily have the two devices recorded to the same file, but with one playing over the other.  

If your mixer allows you to create groups of channels, then it will also help if you want to achieve this (more on that below). 


In general, you will see a mute button or switch on each channel. What this does is simply stop the signal coming into that channel from being sent to the outputs of the mixer.  

This control is that it allows you to silence whole channels without having to adjust all of their controls individually. 

Channel Fader 

These controls are what allow you to adjust the overall level of each channel. Whether you’re using a single stereo-audio output or multiple outputs, these controls will let you balance all of them for optimal volume.  

Master Fader 

These are much like channel faders except that they affect the overall level of the audio coming from the outputs of the mixer. In addition to each output’s volume, you can also control it globally for better volume or effects.  

They can also be used with auxiliaries, which control their overall volume without changing the sound of anything else on your mixer. 

Master Outputs 

These are often the final outputs that the signal will go through. You can just plug them into your speaker system or even a recording device (like a tape recorder, or an interface for your computer). 

Read More: Best USB Mixer For Home Studio


It’s a lot less intimidating than it seems, isn't it? 

Recordists, sound engineers, and producers are always looking for ways to improve their signal chain. 

So, if you were wondering about what each knob and fader on your mixer does, then I hope this article has made it easier for you to understand all these controls. So that you can get back to focusing on recording great audio instead of worrying about how much there is going on with your equipment.