What is Doubling in Audio Engineering?

Doubling is an audio effect used in music production. It makes sounds thicker and fuller. It does this by copying audio tracks and layering them on top of each other. This makes the sounds bigger and more spacious.

Sound engineers and music producers use doubling a lot. It is a common technique. Many famous songs use doubling on instruments and vocals. Doubling can be done in different ways to get different sounds.

How Doubling Works

When you double a sound, you are basically making a copy of it. You then play the copy at the same time as the original. This makes it sound like there are two of the same instrument or vocal. Even though it is the same sound copied, it makes the audio bigger and wider.

The human ear hears the doubled sound and thinks it is coming from a larger source. This is because there are slight differences between the two copies. They are not 100% the same. These tiny differences trick the brain into perceiving a bigger sound.

Doubling works by utilizing the Haas effect (also called the precedence effect). When two similar sounds reach the ear within 40 milliseconds of each other, the brain combines them into one sound. But it still makes the sound seem bigger and wider than a single source.

Ways to Create Doubling

There are a few main ways to create a doubling effect:

Delay

One way is to copy the audio and then delay the second track very slightly. The delay is usually between 10-40 milliseconds. The tracks play together but the slight delay creates the doubling effect. Anything more than 40ms starts to sound like an echo or slapback delay instead of doubling.

Pitch Shift

Another way to double is to copy the audio and slightly pitch shift the second copy. This creates two takes that are almost the same but different enough to sound “doubled”. Usually the second take is shifted only 5-10 cents (hundredths of a semitone). This slight detuning makes it sound thicker. But pitch it too far and it starts to sound out of tune.

Double Tracking

Double tracking means actually recording two separate takes of the same part. The musician plays or sings the part twice. The two takes are then panned apart. This creates a doubling effect. Famous groups like The Beatles and Queen used this technique a lot.

Chorus Effect

Certain effects pedals and plugins can simulate doubling. The most common is a chorus pedal/plugin. Chorus works by combining pitch shifting and delay. It copies the incoming audio multiple times, slightly detunes each copy, and delays each copy by varying amounts. This creates a simulated doubling effect that can range from subtle thickening to very warbly and seasick-sounding depending on the settings.

Reverb

Reverb doesn’t quite create a doubling effect on its own. But it can enhance the space and depth of doubled parts. Sending doubled tracks to the same reverb makes them sound like they are in the same space. This glues the sounds together. The doubled sound is big but still cohesive.

When to Use Doubling

Doubling can be used in many situations. Any time you want a part to sound thicker or wider, doubling might help. Here are some common uses:

Doubling Vocals

Vocals are very often doubled to create a fuller sound. A lead vocal can be doubled to make it more powerful while keeping the intimacy of the solo voice. Backing vocals are almost always doubled or even tripled/quadrupled. This gives backing vocals a choral effect to support the lead.

Doubling Guitars

Electric guitars are also frequently doubled. Two guitars playing the same part makes rhythm parts very thick and heavy. Doubled guitar leads or solos can create a “shredding” effect of fast notes coming from everywhere. Acoustic guitars also take well to doubling to simulate the effect of two guitarists.

Doubling Synths and Keys

Synth pads, string patches, piano, and other keyboard sounds also work well with doubling. The wide stereo image makes these parts very lush and encompassing. The animated chorusing effect created by doubling also gives motion and interest to long sustained notes.

Doubling Drums and Percussion

Drum parts can be doubled to create a massive drum sound. Copy the drum take and pan the two takes hard left and right. The small differences between the performances will add width. Room mics are another way to achieve drum doubling. Percussion parts like shakers or tambourines can also be doubled for a jangle-y effect.

Doubling in Different Genres

Different genres use doubling in different ways:

In rock and metal, guitar, bass and drums are often all doubled for a “wall of sound”. Think of classics like Queen’s “Bohemian Rhapsody” or Metallica’s “Enter Sandman”. The doubled guitars and vocals make the tracks very powerful.

In pop, vocals are the most commonly doubled element. Many pop vocals have at least a subtle double for polish and fullness. The doubled vocals are often quite wide in the stereo field. Britney Spears’ “Baby One More Time” is a good example.

In electronic music, synths are usually the doubled element. Wide, detuned synths are a big part of many genres from trance to dubstep. The doubled synths create a “supersaw” effect. This can be heard in tracks like “Sandstorm” by Darude.

In more acoustic genres like folk and country, a single vocalist or instrument is sometimes doubled to create a small thickening effect. The doubled part might be more towards the center and not as wide. This allows the intimacy to be kept while adding some heft to the sound.

How Much Doubling is Too Much?

Knowing when not to double is important too. Not everything needs to be doubled. In sparse arrangements, a single vocal or instrument can be more powerful on its own. Doubled vocals can sometimes obscure the lyrics. Doubled heavy guitars can make the low end too muddy. Sometimes the mix just gets too cluttered if too many parts are doubled.

If unsure, try muting the doubled part. See if the mix has more impact, clarity and punch without it. Let the genre and the song arrangement be the guide. Busier mixes have less space for doubling. Sparser mixes may have more room for doubling to add interest.

Imperfect Doubling

Doubling doesn’t have to always be perfect. In fact, sometimes looseness is the goal. The slight variations are what makes it sound human and natural. Two separately recorded takes will never be 100% locked. That’s okay.

When double tracking, the timing of the two takes is allowed to ebb and flow. The same with tuning. If it’s too perfect, it will just sound like one take. Let little imperfections through, as long as the overall take still sits together. Pocketing is good.

Doubling in a DAW

Most doubling today is done in a digital audio workstation (DAW). All DAWs have tools that make doubling easy:

You can duplicate the clip/region and create two tracks. Then you can nudge one clip a few milliseconds later. For double-tracked vocals or guitars, just record two separate takes and pan them left and right.

All DAWs have pitch shifting built in. You can detune by cents right in the DAW. They also have chorus, flanging, and doubling effects. These can simulate the effect without actually copying the track. Just add the plugin and adjust the settings.

Some DAWs even have specific “doubler” effects. These simulate double tracking by duplicating the incoming audio and delaying and detuning it. This makes it easy to get the sound without manually copying tracks. Good for quick demos or just experimenting.