Mixing on
Headphones
This short eBook is focused on helping you make the best decisions while mixing on headphones. This will include some tips, tricks & suggestions what to keep an ear out for.
Mixing on headphones
1
Can You Mix Effectively On Headphones?
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Mixing on headphones
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Can You Mix Effectively On Headphones?
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The answer is yes;
you can create a commercial-quality mix on headphones – with properly calibrated frequency response and a little know-how.
 
1.1. Coping With Acoustic Issue
For the small studio owner, achieving professional-quality mixes is an elusive goal for many reasons, not the least of which, being inaccurate budget monitors and acoustically problematic rooms. Even professional mixers with access to the best equipment experience environmental problems. It's fair to say that most home studio owners aren't going to have financial resources or the work to spend multiple thousands of dollars to perfectly treat and tune the room. The good news is that you don't need to. Room limitations can be overcome easily and inexpensively by mixing on headphones. Since headphones create an isolated environment, room resonances and comb filtering effects, which compromise your ability make proper tonal and spatial mix judgments, are no longer an issue.
1.2. Flattening Frequency Response For Flattering Mix Decisions
With headphones, it's easy to hear subtlety and nuance, which is why professional mixers use them to check fine details. For example, headphones make it easier to hear small and quick audio dropouts, bad edits, unnatural crossfades, and fader automation over/undershoots. Ported budget monitors are another problem that plague small studio owners. Ports are designed to compensate for lack of bass projected by small woofers. On budget monitor designs, which tend to cut corners to keep prices down, the bass reflex ports can create unwanted resonances that combine with direct sound. These resonances extend into, and thicken the low midrange, prompting you to cut low mids more than necessary. The result is a thin-sounding mix that lacks punch.
1.3. The Devil Is in the Details... and Low Mids

Based on the information so far, it may sound as though headphones are all sunshine and puppy dogs, but they are not without conditions to overcome. The most important one that needs to be addressed is their frequency response as opposed to that of studio monitors. Speakers, when properly designed and placed correctly in the room, provide a flatter frequency response than headphones, which is crucial to making proper mix decisions.

To overcome the limits of small transducers in headphone ear cups, the frequency response of most commercial headphones tends to be exaggerated in the bass, with varied performance throughout the rest of the spectrum. This non-linear response makes them difficult to use for effective mixing. Even studio oriented headphones are guilty of the same habit!

As you can see in the illustration below, the frequency response of 10 popular professional studio headphones varies up to 10 dB at different points along the spectrum, which will also adversely affect mix decisions. Fortunately, a headphone calibration plugin, such as the Sonarworks Reference 4, can flatten the frequency response of any headphone, making them perfectly viable mixing tools.

To recap, if you are using budget speakers in an untreated room, headphones not only enable you to take unforgiving room acoustics out of the equation, they can take the place of expensive monitors, giving you a flat frequency response across the audible spectrum (provided you're using them with Sonarworks calibration software). The elimination of room characteristics combined with the flat frequency response achieved by headphone calibration ensures that sound quality and tonal decisions will be more reliable across the board.
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Mixing on headphones
2
How to Get a Spacious Mix Using Headphones
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Mixing on headphones
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How to Get a Spacious Mix Using Headphones
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Learn how to create a 3-dimensional mix with reverb and delay and the advantages of doing it with headphones.
 
2.1. Creating a Satisfying Illusion for the Listener

The dimensionality of a mix is a very important concept that tends to escape the amateur mix. A two-dimensional mix is not wrong per se, but a three-dimensional mix creates the illusion of music occurring in reality space, which is quite simply a more satisfying listening experience. And yes, the title of the article is a nod to Doctor Who fans.

Our ability to perceive three-dimensional space with speakers is limited due to physical characteristics of the room they're in. Reflections, distance between the speakers, the natural reverb of the room, plus the position of the listener, tend to smear our ability to hear a three-dimensional soundscape on speakers.

With headphones, the "space," as some of your parents might have told you, exists solely between your ears. By eliminating room reflections and variations in your listening position relative to the speakers, headphones make it easier to hear and control the spatial aspects of a mix.

To quote Dr. Richard Heyser, "The effect that modern sound reproduction strives to achieve is the creation of an acceptable illusion in the mind of the listener."

With headphones, since it's much easier to hear and control the three-dimensional qualities of a mix, it follows that headphone mixing is the key to creating an engaging and satisfying illusion of sound moving in reality space.

2.2. Opening Dimensional Doorways

To make a mix three dimensional, we have several tools to work with.However, the most important in terms of the front-to-back placement of sound in a virtual soundstage are time-based effects. Time-based effects include reverb and delays. While we do have other means to bring sounds forward or backward in a mix, such as volume, EQ, distortion, transient modification, pitch shift, and enhancement, nothing creates the illusion of 3-dimensional space like reverb and delay.

Beyond creating the illusion of space, reverb has a few uses, which include blending instruments; thickening; creating size; making tonal changes; and adding sustain to an instrument or voice. Reverb can also be used to create rhythmic effects as well.

However, the most common use of reverb is to place an instrument in a soundstage, since the first noticeable effect that reverb has on a sound is to push it backward in a mix. The problem is that using reverb to move sounds forward and back is not as effective as delays are due to its masking effect, particularly when over used. Do not overlook the pre-delay in reverbs to avoid masking the source too much.

2.3. Reverb, Delay and Pre-Delay

To make a mix three dimensional, we have several tools to work with.However, the most important in terms of the front-to-back placement of sound in a virtual soundstage are time-based effects. Time-based effects include reverb and delays. While we do have other means to bring sounds forward or backward in a mix, such as volume, EQ, distortion, transient modification, pitch shift, and enhancement, nothing creates the illusion of 3-dimensional space like reverb and delay.

Beyond creating the illusion of space, reverb has a few uses, which include blending instruments; thickening; creating size; making tonal changes; and adding sustain to an instrument or voice. Reverb can also be used to create rhythmic effects as well.

However, the most common use of reverb is to place an instrument in a soundstage, since the first noticeable effect that reverb has on a sound is to push it backward in a mix. The problem is that using reverb to move sounds forward and back is not as effective as delays are due to its masking effect, particularly when over used. Do not overlook the pre-delay in reverbs to avoid masking the source too much.

Long pre-delays have the added advantage of defeating the masking effects of reverb, providing a more defined sound and a cleaner mix.Since pre-delay is measured in milliseconds, a 20ms pre-delay puts the back wall approximately 20 feet away. Keep in mind that in an actual room, there's no guarantee that sound is going to hit the back wall first.

However, don't forget that sound between stereo speakers is an illusion, and in our virtual space, since the reflections of reverb are so complex, we don't hear sound coming from one side or the other, but rather from front to back, which is more clearly defined by pre-delay. Using pre-delay, we now have a means to place instruments in different positions in the sound field with the added advantage of clarifying them by allowing us to hear the dry sound before the reverb sets in.

2.4. Creating a BackWall With Delay
A single mono delay will create a "back wall" for a given sound source to help you define the front-to back dimension of your virtual soundstage. Since lead vocals are often the front-most focus of a song, they determine the depth of your soundstage. Therefore, the place to start is to create a back wall for your vocals. A common delay setting for vocals is to use an 8th-note mono delay timed to the song's tempo.
If you don't have the ability to select notes as delay values, though nearly all delay plug-ins do, you can either find delay calculators online, or use the formula, 60,000 / BPM = delay (in milliseconds). Keep in mind that this formula will give you the delay time for a quarter note in 4/4 time. Sixty thousand is the number of milliseconds in one minute, and a quarter note equals one beat in 4/4. Therefore, at 120 BPM, a quarter note is 500 ms and an eighth note would be half that, or 250ms. When setting pre-delays for reverb, it's best to use shorter settings, say between 20-25 ms. If you don't have a pre-delay setting on your reverb, just put a delay in front of it, et voila, instant pre-delay.
 
Mixing on headphones
3
Referencing Reverb On Headphones
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Mixing on headphones
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Referencing Reverb On Headphones
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How to make proper decisions regarding type and amount of reverb when mixing on headphones.
 
3.1. Referencing Reverb On Headphones
Nothing makes judgments regarding the application of reverb in a mix easier than headphones. However, since you'll be able to hear those long reverb tails clearly, you'll either be tempted to go overboard, because the reverb sounds so good, or you might dial back the amount of reverb because it's so clearly audible. What's a mixer to do? While both warnings have an element of truth, they fail to mention that it's not just a matter of quantity of reverb; it's also a matter of quality. "Quality" in this case refers to the density or sonic texture of reverb decaying over time.
The parameter that controls density varies with different manufacturers. For example, on Lexicon reverbs, "Definition" controls density, whereas on the Sonnox reverb plug-ins, the control parameter is "Dispersion." What you're looking for are low-density reverb tails. Think of low-density reverb like Swiss cheese, with lots of holes in it, and high density like smooth peanut butter. In nearly every case, with the exception of a desired special effect, a low-density reverb is preferable.
3.2. Reverb Is Not Just for Speakers

Reverbs in a mix don't live in isolation during playback over speakers.They actually join with the natural reverb of the room. If you use a thick, creamy-smooth reverb, it will combine with the room's reverb and pull its associated instrument backward in the mix. The larger the room, the more its natural reverb combines with the mix reverb. The holes in a low-density reverb will be filled with the room reverb, creating a seamless join, and will have the effect of bringing the parent sound closer. The isolation afforded by headphones takes this phenomenon out of the equation, but it should be taken into account in order for your mixes to translate properly to speakers. Therefore, as a basic rule, stick with the low-density reverbs.

Another thing to consider is that long, smooth reverb tails require more volume to hear, which in turn takes up more space in the mix, plus, they have a masking effect on all surrounding sounds. Since we have limited space in a mix, anything that isn't heard is just wasting resources—and that provides a clue for determining the length of reverb tails. Once a reverb tail is no longer heard in the mix, there's no reason for it to continue beyond that point.

When deciding the length of a reverb tail, make sure you end it in a musical fashion. For example, if a reverb tail continues for two measures, but is only heard for one, end the tail on or slightly after the downbeat of the second measure. Ending it before the downbeat will create an unmusical empty space with the uneasy feeling of stopping short, but extending it to the downbeat will have the effect of a wave pushing the rhythm to the next measure.

3.3. Widening Effects of Reverb

A trick for adding stereo width to a sound with reverb is to create two aux tracks in your DAW and use a different reverb plug-in on each aux track with different types of reverb. Pan one aux reverb left, the other right, and assign the dry sound source to each. You can further expand on this concept by using three mono reverbs, which is based on a technique created by 23-time Grammy-winning engineer Al Schmitt (Steely Dan, Toto, Henry Mancini), who would take the mono live chamber reverbs at Capitol Studios and spread as many as eight sends across the stereo field. (Hard left/right, center, a couple mid left-center, and couple mid right-center. More than likely, Al used as many as eight mono reverbs to mix large ensembles, assigning different instrument groups to each send based on their actual physical position.

Since we're mixing on headphones, it will be easier to hear the effects of the multi-mono reverb trick, but before you go all Al Schmitt on your tracks, try using the dual mono reverb to widen synth pads. Save the three mono reverbs for vocals, with a spring reverb up the middle, large room on one side, and medium room on the other. For a good jumping off point, set a 50ms pre-delay on the center reverb, 8ms on the large room, and no pre-delay on the medium room. Of course, you should experiment.

3.4. Bonus Tip: Abbey Road Reverb

High-frequency tails of long reverbs can annoy and detract (unless it's the effect you're going for). At Abbey Road studios, it's been a long-time practice to filter high and low frequencies on the input side of reverb aux channels, which creates a subtle, natural-sounding reverb. Try this on vocals: Set a high-pass filter at a -12dB per octave slope to cut everything below 600 Hz or so and a low-pass filter to cut everything above 4k-5kHz plus or minus depending on the sound. Et voila, instant Abbey Road reverb.

The important thing to listen for is how the cuts to low and high frequencies make you feel. For example, as you cut lows, apart from increased clarity, pay attention to the emotional impact and feel. You may find the vocal sounding not only bigger, more intimate and nuanced as you increase the center frequency. With high-frequency cuts, remember that 4k-5kHz is just a ballpark number. You might want to leave frequencies up to 6kHz for the sake of bringing out air in an instrument or breathiness in a female vocal. Again, each sound is different and requires some experimentation.

 
Mixing on headphones
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How to Make Panning Decisions in Headphone Mixing
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Mixing on headphones
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How to Make Panning Decisions in Headphone Mixing
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How differences in stereo perception between studio monitors and headphones affect panning decisions ... or do they?
 
4.1. Better Hearing Through Headphones

You might wonder why, in the early days of stereo, mix engineers went to so much trouble to create a dimensional stereo mix, particularly when what they heard in the studio was never going be heard the same way on the available commercial playback systems. The reason was headphones.

In 1958, jazz musician John C Koss invented the first stereo headphones so that home listeners could get the most out a newly burgeoning technology called, "LPs." As music grew in the '60s to become the most dominant force of expression for a generation, the use of headphones grew along with it – particularly when it was discovered that headphones and certain natural substances provided a most unique and immersive listening experience. Today, headphones and ear buds have taken over as the primary listening medium, which alone makes a good argument for mixing on headphones.

4.2. Perception and the Illusion of Stereo

As sound researcher, Dr. Richard Heyser* said; "The actual sound field in a listening environment is not identical to the sound field which we may perceive..." He also went on to say, "If we wish to understand how to 'measure' what we 'hear,' then we must deal with subjective perception and the illusion of sound."

Dr. Heyser's observation particularly applies to the difference of stereo perception between speakers and headphones. Due to cross-feed, which is sound from a speaker on one side of the stereo field reaching the opposite ear, we perceive the stereo field at approximately a 60-degree angle from center position to left and right speaker (see the image below). Headphones eliminate cross-feed, so that our perception of the stereo field is 180 degrees, which in turn causes us to perceive the center image inside our head. While it may be argued that the isolation of headphones makes for an unnatural listening environment, keep in mind that stereo coming from speakers is a non-reality as well. At the end of the day, all we really have with stereo speakers are left and right. The center image and everything in between is a ghost that becomes less substantial as you move between speakers.

Since we perceive stereo sound differently in headphones than in speakers, conventional wisdom suggests that one might pan instruments differently, or even improperly, but it really doesn't have to affect your panning decisions. Experienced mixers make panning choices based on a pre-imagined soundstage, not the geometry of speakers. They "see" the left-to-right position of instruments in their head and then make the appropriate panning choices.

4.3. A Panning Schema That Transcends Monitoring

There is a panning scheme used by professionals that completely obviates concerns regarding panning decisions in either medium, which is LCR (left-center-right) mixing. LCR mixing consists simply of panning all elements of a mix left, center, or right. LCR mixing has been a component of hit songs for decades and continues to be. For example, The Beatles "Strawberry Fields Forever," "A Day In The Life," and Jimi Hendrix' "Purple Haze" are examples of LCR mixing. A-list mixer Chris Lord-Alge also mixes in LCR.

The only exception in LCR mixing would be panning to mid center-left or mid-center right in the case of background vocals or certain percussion instruments. Mid center/left and mid center/right are products of level differences between left and right, and as such, as we move closer to one speaker or the other, instruments panned there lose their position in the stereo field, sounding as though they're coming directly from the speaker you're closest to.

4.4. Precision Panning

With large-format analog consoles, apart from issues of perception based on position between the speakers, the variances in the response of pan pots made accurate mid-left and mid-right positioning difficult. To overcome these inaccuracies, precision panning was achieved by sending a sine wave to designated left and right channels and adjusting the pan controls until the levels matched.

These days in DAWs, precision panning assignments are easily made numerically. However, physical movement between speakers can still obscure the results, particularly if you're working in an untreated environment. Therein lies another advantage that mixing in headphones provides; you take the sweet spot with you wherever you go. What this means to the headphone mixer is that you can more easily get the same stereo results you would have to work harder to achieve with loudspeakers. You can also hear the end game of your panning as you work.

 
Mixing on headphones
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What to look out for when mixing on headphones
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Mixing on headphones
5
What to look out for when mixing on headphones
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Make your mixing time on headphones worth your while!
 
Take breaks!
There is no reason for you to work more than ~1 hour without taking a break where you let your ears reset. Some might say that this is losing you time, but it will actually save it. Why? When we're using our ears, they get tired, like any normal muscle would and our brains are less sensitive to what we're hearing. This is why taking frequent 10-15minute breaks can help you spend less time hunting for ghosts and stay objective to the decisions you make during the mixing process.
Reference as much as you can

This is a golden rule for every type of audio work and the best way to ensure that you stay true to the end-goal. Cannot decide if that vocal delay works? Does this snare need more reverb? Listen to a different mix with similar effect to what you want to achieve and compare. Things will more easily stand out if they don't fit into your mix when compared to a commercial, well balanced mix. But make sure to have both your and reference mix level matched!

If you follow the guidelines presented in this eBook and the two, I'd even say, golden rules, there shouldn't be much to worry about when it's time to mix on headphones. Specially, with Reference 4 Headphone calibration applied, you can be sure that every decision you make, will be the right one.