Iconic movie sound effects, your favorite songs, and ambient background noises are created through the art of audio mixing. From lo-fi to hi-fi and everything in between, here’s the lowdown on the high stakes world of sound mixing—and how to get started crafting quality audio.
Audio or sound mixing is the process of combining multiple recordings or tracks into an arrangement called a multi-track or a mix. Adept audio mixing requires delicate and deliberate balancing and takes years to master. “Mixing is: ‘We’ve got the ingredients, let’s choose how to bake this cake,’ ” explains sound designer and re-recording mixer Johnnie Burns (“Nope,” “The Favourite”) about the process of combining audio elements into a mix. Professional projects use dedicated audio engineers to craft exemplary mixes for music, film, TV, video games, podcasts, social media content, and radio.
Music mixing entails balancing and editing recorded vocals and instrumentals after tracking. Music mixers add audio effects such as reverb and distortion, edit out any auditory errors, and balance the volume so that no instrument steals the show from the others.
For film and TV, music mixing is used to set tone and mood. “I use all different flavors of the sounds of the instruments, of the balance of the instruments, and the tonality,” says music engineer John Rodd (“Nope,” “Get Out”). “Should the brass be more muted sounding, [or] should it be brighter sounding? Should the trumpet sound heroic with a long reverb on it, or should it be intimate and in your face and aggressive because the alien spaceship is coming?” These decisions change the way viewers perceive visual elements.
Ambient sounds ground a scene and help it feel realistic. For example, if a scene takes place on a busy New York street, background noise such as cars honking, wheels screeching, and pigeons cooing helps create a visceral sense of realism. Some sound designers will even film takes without any dialogue just to get a recording of ambient sounds that they can later loop into the mix.
On top of dialogue recorded during production, automated dialogue replacement (commonly referred to as ADR) and voiceovers are sometimes added in postproduction. ADR replaces poorly recorded dialogue or inserts additional dialogue that wasn’t initially recorded. However, ADR is typically employed as infrequently as possible during the sound mixing process. “The last thing you want to do is ask an actor six months later to give credibility to a rerecording of some incredibly emotional or moving scene, because it’s going to be almost impossible to put them back there,” Burns says.
Sound effects are bits of audio that add narrative believability or convey emotions. Audio mixers either take advantage of the wide variety of sound effect libraries available or create their own custom ones. Sound designers or engineers might also choose to embellish a sound effect, such as making a gunshot punchier in a shootout scene in order to make it more cinematic.
Foley sounds are a manufactured subset of sound effects that bring actions to auditory life. Foley artists might recreate audio for elements such as clothes rustling, footsteps, or lightsaber swishes. For example, the iconic humming of the lightsabers in “Star Wars” was created by combining simplex projector sounds with the signal transmitted between an old TV set and microphone.
Studio mixing in postproduction is the most common form of audio mixing. Although working in a studio is by no means simple, it has the benefit of a much longer turnaround—meaning extra time to set up equipment, rearrange it when necessary, and try out different ideas with the mix.
Working a live event such as a concert, live radio show, or live album leaves little room for error. This means that it’s crucial to conduct sound checks and set up all equipment well in advance of the actual event. If something breaks or stops working, the sound team has to quickly come up with solutions.
Performance and venue type also affect the live mixing process. Audio mixers at a concert, for instance, must consider how venue acoustics will shift once the seats are filled with spectators.
Pavel L Photo and Video/Shutterstock
Project sound can only be perfected through deliberate curation. Even if every track is recorded perfectly, that might all go to waste without a well-balanced mix.
Sound quality matters
While the highest fidelity audio isn’t necessary to create compelling mixes, sound quality does matter. Good sound is balanced and lacks mistakes, which fosters greater audience immersion.
While you might be able to get away with poorly mixed sound in a visual medium like TV or movies, there’s less room to hide in formats that are purely audio. Music, podcasts, and radio don’t have visuals to split the attention of the viewer. “With music, it has to be far more clinical and much more subject to scrutiny,” Burns says.
Mixing creates the right tonal balance
Not every project calls for the same tonal balance (or intensity throughout the range of frequencies). Different genres— such as action movies and dramas, or hip-hop and country—adhere to different sonic styles. Without audio mixing, the sound would be subject to some undeniable flaws in balance, such as:
- Muddiness: When too many tracks crowd the same range of frequencies, it muddies the sound and makes it difficult to hear each one individually.
- Thinness: On the other hand, if tracks are spread out too far, the mix will sound thin. This means that the audio sonic space lacks depth and is overly compressed. A thin mix might be the result of an underdone arrangement or low-quality recordings. These can be mitigated by applying effects such as delay or distortion. However, overdoing these effects can also warp and overprocess the sound.
- Overprocessing: When effects are overused, the audio sounds gratingly overprocessed. An efficient way to create a balance between the different levels of sound is to alter the volume and frequency of each track.
It brings greater meaning to sound
Ultimately, audio mixers are responsible for embellishing raw auditory material in a way that emphasizes the intended tone of the project. Mixers don’t just assemble the tracks and tweak the sound; they also use those sounds to evoke a specific time and space. A good mix doesn’t just curate audio—it elevates it. “I’m not the composer; I’m just shaping how the music sounds and how it affects you emotionally,” says Rodd.
Audio mastering is the final postproduction step after audio mixing. Mastering entails fine-tuning audio to the desired thematic tone of the project and giving it a final round of revisions for any remaining errors and unwanted sounds. “It’s about making sure things have a really smooth flow” by polishing the mix and elevating it, says Burns. Directors, editors, and engineers may become involved in the audio mastering process, depending on the project.
Pavel L Photo and Video/Shutterstock
To mix audio:
1. Acquire tracks
Larger projects often have dedicated sound designers and/or composers who create and collect all the audio tracks, but smaller projects might have the sound engineer record and edit tracks. Aiming for high-quality recordings and clear, crisp sound gives yourself the best foundation to work with.
2. Edit tracks
After a recording has been done, audio engineers edit each individual track as they see fit. This might include removing sections, splicing tracks together, or emphasizing parts of the range of frequencies, which are broadly classified under the groupings of treble, midrange, and bass.
3. Choose your weapon
- Mixing console: Of course, you can’t mix audio without a mixing console. These come in two different varieties: digital audio workstations (DAWs) and analog mixing consoles. The former are far more accessible and cheaper than the latter, which are typically found in professional studios.
- Headphones: Since you’ll be doing a lot of listening, it’s also worth investing in good headphones. Just be sure not to damage your ears by turning the volume up too loud.
4. Begin mixing
Once you’re all set up, you can start combining, splicing, and adjusting your tracks, which usually begins with adjusting the volume and panning (i.e., the distribution of sound across the channels of a stereo field). After that, it’s up to you where to take the mix and what effects to use.
- EQ is short for equalization and is the most common tool in an engineer's arsenal. It can get pretty complicated when you get into the details of its use, but to put it simply, EQ is used to alter the frequencies and gain (the level of amplification) in sounds. By fine-tuning these elements, which are measured in hertz (Hz) and decibels (dB), engineers can clear up muddyness and harshness.
- Compression reduces the difference between the softest and loudest segments of a track (the audio dynamic range), resulting in better balance. That way, all the tracks can be heard.
- Reverb adds space and depth to audio by replicating the effect that occurs from sound reflecting across physical surfaces. This effect is used to give depth to the mix and create sonic space.
“One of the great things about my job is… it’s never the same,” says Rodd. “I’m always inventing new ways to sculpt sound, new chains of software or hardware to create interesting and different and evocative sounds to help create emotions with the music.” Experimentation can lead to interesting and new paths for the mix. However, it’s also important to keep the creative and technical goals of the project in mind. The process becomes more efficient when the sound mixer and other members of the sound department understand what they’re working toward, so developing a deep understanding of what the project leader is looking for is a must.
These expert tips will have you mixing audio like a pro:
- Use a reference mix: A reference mix is a completed audio file that you can use as an example or template for your own work. Choose something that closely resembles what you want your finished project to sound like in terms of tone and style.
- Get the right plug-ins: Plug-ins are software programs used to enhance audio processing in DAWs. There are multiple plug-ins available for every kind of effect and method of sound engineering, and some are even available to download for free.
- Stay organized: When you’re working with a lot of tracks and different mix versions over a long period of time, things tend to get misplaced. Be sure to label everything and remember where all the files are stored.
- Know what you’re working towards: Creative projects benefit from a strong sense of purpose and a clearly defined goal. “I look at it in terms of what is narratively useful to focus on,” Burns says. Carefully consider what story you’re trying to create with your audio mix to provide yourself with structure.
- Make the most out of a tricky situation: If you’re stuck with a less-than-ideal recording that has unwanted sounds in it, there are still ways to work around it or with it. “Usually, with bad recordings, you try and find a way to introduce the noise you have to put up with,” says Burns. “It’s all about tricking the ear.”