What is Mixing?
Mixing is the craft of taking multiple audio tracks and combining them together onto a final master track—be it a 2-channel stereo master, or 6+ channels in the case of surround mixing. The way we combine tracks is equal parts art and science, and involves utilising a variety of tools to bring out the most emotional impact from the song or soundtrack.

Mixing can be as simple as presenting great-sounding tracks in a more impactful way. Other times, mixing may require repairing tracks that sound sub-par. Each mix presents its own problems and challenges—it’s your job as the mixer to not only solve these problems, but to present the material in the way it sounds in the client’s imagination.

The Four Elements of Mixing

Think of a mix as a sonic three-dimensional image. There are four essential elements that we use to control that image:

1. Level (Height)
2. EQ (Height)
3. Panning (Width)
4. Time-Based Effects (Depth)

Level
Level seems pretty simple—when we want to hear something louder, we turn up a fader. And the louder components of the mix grab the listener’s attention more than the quieter components.

EQ
EQ is really just a more detailed level control that lets us boost and cut levels at specific frequencies. EQ is the easiest way to shape the tracks in your mix so they fit together—and provides a powerful way to add personality and character to the individual tracks. Most equalizers allow independent control of the three most common variables: amplitude, center frequency and bandwidth.

Panning
If you were to think of level and EQ as the vertical (up/down) elements, panning would be the horizontal (left/right) element. Panning can be very helpful for elements that sit in the same frequency range. By panning one to the left and the other to the right, you can separate the two instruments or FX and reduce the chance of one sound masking the other, and making it harder to hear.

Time-Based Effects
Time-based effects form the element of depth (front to back). Time-based effects such as reverb and delay can make sounds seem further away, or sometimes bigger than a dry recording.

So utilizing the four elements we have control over and changing them throughout a song or show’s structure can result in a vibrant and dynamic mix. Mixing involves a fair amount of sleight of hand—you’re deciding what elements the listener is focusing on and you can change their focus within the mix at any point. A good example of this is going from a vocal melody to another instrument soloing. You’ve now seamlessly taken the attention of the listener from the vocal to the solo. For TV, changing the EQ can instantly take you outside of the room you were just in.

Equalization (EQ)

PRINCIPLES OF EQ
There are many different types of equalizers, and they all perform boosts and cuts in specific frequency ranges. The frequency range can be divided into several bands, such as a low band, a high band, and so on. This allows for unique adjustments to be made in certain areas. Equalizers usually consist of several bands: each band of an EQ is a single filter.

THE ART OF EQ
Let’s take a look at some general EQ tips.

• If your mix feels “muddy”, try reducing frequencies between 125Hz and 500Hz. If certain instruments or SFX, such as heavy electric guitars, piano, or a background ambience feel as though they are carrying too much “weight” in the mix, start with those sounds.
• Too much between 500Hz and 1kHz can sound “woody” or “boxy” and give a false sense of power in a mix.
• Watch your step with 2kHz and above. This is an area where a little EQ can help a lot, while a little too much can start to make a mix sound brash or tinny.
• Remember that “cutting” can be just as effective as boosting—and oftentimes even more effective. Think of carving out a comfortable place for any dialog to sit.

Dynamics
Dynamics processing isn’t just about making things ‘louder’. In the context of mixing, dynamics processing can be used to control the dynamic range of an audio signal in order to achieve a variety of auditory effects. You can think of dynamics processing as having two major ‘families’: Downward Compression/Limiting and Expansion/Gating.

WHAT ARE DYNAMICS FOR?
Using these processors is a way to control, reduce or expand the dynamic range or overall volume level of a track.

In the case of compression and limiting, the goal is usually to “even out” the dynamic range of a track by attenuating loud transient peaks, such as a singer that suddenly belts out a high note or an actor putting a bit too much into the performance.

In the case of expansion and gating, the goal is to lessen or remove unwanted signal on a track. Removing the sound of high hat bleed in a snare drum recording would be one example. Reducing the volume of unwanted breaths in the dialog would be another.

PRINCIPLES OF DYNAMICS
The ability of a good mixing engineer to use dynamics processing effectively is truly a life-long learning process. So let’s start with the four basic parameters common to almost all dynamics tools, namely, threshold, ratio, attack and release.

• THRESHOLD– The threshold is the level at which dynamics processing begins. For compressors and limiters, any signal rising above the threshold would be affected. For expanders and gates, any signal falling below the threshold would be affected.
• RATIO – The ratio determines the amount of dynamics processing that happens to the signal. For example, a 4:1 ratio on a downward compressor means that for every 4dB the signal in question rises above the threshold only 1dB will be heard above the threshold, a reduction of 3dB.
• ATTACK – The Attack parameter defines how fast the dynamics processor works once the signal has passed the threshold, usually measured in milliseconds.
• RELEASE – The Release parameter determines how fast or slow the dynamics processor stops processing or “let’s go” once the signal has passed the threshold, also measured in milliseconds.
  

THE ART OF DYNAMICS PROCESSING

• Use lower ratios (2:1 – 5:1) for “levelling out” performances, particularly ones that have a few notes that “jump out” in a particular performance.
• Try this on a lead vocal: first, set a limiter with a high ratio to grab the extremely hard peaks and then follow it with a compressor using a gentler ratio (say 3:1) to do the overall processing. This will allow the compressor to not work as hard on those peaks, and the voice will sound less ‘pumping’ and more natural. 

Panning / Stereo Imaging
If we think of Level and EQ as the ‘height’ or ‘vertical’ part of our mix equation, panning is the ‘width’ or ‘horizontal’ part of our mix equation. While music is typically mixed and listened to in stereo, TV and film sound is routinely mixed in a surround format. Panning a single audio element within a mix is the process of weighting the element more heavily in favor of the left, right, center, subwoofer, or rear/side speakers.

WHAT IS PANNING FOR?
Panning in large part determines how wide our mix ends up sounding to the listener. It can be used to create space in a mix, enhance existing space, and create a more immersive experience for the audience.

PRINCIPLES OF PANNING
How do we know what to pan, and where? A general rule in much of today’s popular music is that the backbeat and lead vocal are the focal points of the mix. Because of this, the kick, snare and lead vocal/dialog are usually panned center, often referred to as ‘C’ or ‘0’ by most DAWs.

• Like EQ, panning is another way in which mixers keep elements apart from each other that may otherwise be competing.
• In TV and film, panning typically mimics what is seen (or not seen) on the screen from the perspective of an object or person’s location.
• As a general rule, less is more when it comes to dynamic panning. Active panning only really useful for cars and spaceships whizzing past!
• Every once in a while, listen to your mix in mono to ensure you aren’t losing too much in the translation. It’s possible to spend a long time panning everything, only to go too far and realize your mix sounded more impactful before you even began!

Time-Based Effects
As opposed to the vertical and horizontal dimensions we’ve discussed, time-based effects are responsible for the perceived ‘depth’ in our mix.

WHAT ARE TIME-BASED EFFECTS FOR?
Using different time-based effects can give instruments and SFX the sense of being larger or further away in the mix. Overall, you might say time-based effects are for enhancing the depth, adding the final finishing touches, or providing the final sparkle to a mix.

PRINCIPLES OF TIME-BASED EFFECTS
There are many different types of time-based effects, and though each manipulates frequency content in the time domain, they each work differently and achieve different results:

Reverb
Reverberation is a naturally occurring phenomenon caused by sound reflecting (or ‘bouncing’) off walls in any given room or space. Reverb in the mixing process creates the sense of space that a room would provide and is an aesthetic tool the mix engineer can use to great advantage. 

Delay
A delay stores a signal for a period of time and then releases it. Controlling multiple delay lines allows a mix engineer to create ‘echo-style’ effects.

Releasing the delayed signal with some sort of volume decay enhances the presence of a human voice rather than replacing it, which would make it appear out of time.

For much greater detail and many more tips, please download the comprehensive free “Mixing with iZotope” eBook or PDF, which contains specific examples and pictures covering the above topics in much greater detail at: https://www.izotope.com/en/support/support-resources/guides/