Binaural Audio Dummy Head with line representing sound entering the ear.

What is Binaural Audio? 3D Sound Demystified.

You may have encountered the term binaural audio. But what exactly is binaural audio, and how does it differ from stereo? In this article, I’ll explain the science behind binaural audio and share my practical experience using it to record wildlife soundscapes and nature sounds.

Binaural audio is an amazing recording technique that captures an environment’s three-dimensional space with utmost realism. When played back, the listener experiences identically immersive sound as if they were physically present where and when the recording was made. It is exceptionally true-to-life, which is why it is sometimes referred to as 3d audio.

How does binaural audio achieve such realism?

It’s all about replicating how humans hear. Binaural recordings employ a dummy head using two microphones positioned inside the ear canals of artificial human ears – identical in size, shape, and texture to real human ears. The ridges along the outer ear, called pinnae, gather, amplify, and direct sound waves into the ear canal (or microphone) and create micro-delays that help pinpoint a sound’s location.

The dummy head, similar in size, shape, and density to our own, acts as an acoustic baffle that filters sound frequencies arriving in our ear. Higher frequencies are blocked, while lower frequencies pass through and around the head. The head also influences the volume of sound reaching the ear, known as Inter-Aural Level Differences, and the time it takes for a sound to arrive, known as Inter-Aural Arrival Time Differences.

Binaural Head Shadow

Low frequencies wrap around the head while high frequencies are absorbed.

Outer Ear Pinnae and ear Canal

Pinnae help pinpoint the location of a sound and direct it into the ear canal.

Together, these interactions are referred to as Head Related Transfer Functions or HRTF, which are unique to everyone. This is why recording an environment employing your own head creates the most accurate binaural effect. In practice, however, a dummy head is more suitable to minimize handling noise and image shifts while recording.

Neumann Binaural Head aka Fritz

The Neumann KU-100 strives to address the wide variations found in human head shapes and sizes. It is praised for its optimization and precision of the stereo field.

What’s important to note is that binaural recording accounts for sound arriving from all directions, including above and below. This results in a surround sound experience, but unlike surround sound, it uses only two channels to deliver full immersion. No special equipment or multispeaker setup is required making it particularly accessible to listeners with headphones. In fact, headphones are the ideal choice!

While binaural audio can be listened to using stereo speakers, the accuracy of the image and frequency response will be negatively impacted. This is partly because:

  1. 1The head of the listener produces a secondary acoustic shadow.
  2. 2The listeners’ playback speakers produce acoustic crosstalk that would not be present with headphones.
  3. 3The room acoustics distort spatial cues by affecting the accuracy of arrival times.

These issues are avoided altogether when listening with headphones.

Is binaural audio the same as stereo? 

Binaural audio is stereo, but traditional stereo differs in its capture technique. Notably, Head Related Transfer Functions, critical in binaural recording, are predominantly absent in conventional stereo recording. When done well, conventional stereo recordings have a wide soundfield but capture sound on only the horizontal XY plane. In other words, sounds arriving from the left and right. No differentiation is made from sound arriving on the vertical axis, i.e., above and below. The capture of sounds from behind depends on the microphone’s polar pattern and stereo technique employed.

Stereo PlaneImmersive 3D Binaural Plane

Like binaural, stereo uses two microphones but can be angled and placed at different distances. The distance and degree of angle dramatically affect the width of the stereo image. This can be used to your advantage, for example, if you want to make something sound hyper-real or conversely intimate.

Traditional stereo techniques do not commonly use a baffle between their microphones. When they do, it creates an acoustic shadow that blocks sound, similar to the human head in a binaural recording. When a baffle is used, it is often considered a pseudo-binaural recording. The Jecklin disc and the Crown SASS microphone are examples of a pseudo-binaural method.

Crown SASS Microphone simulates binaural recording techniquesCrown SASS Microphone

Listen closely to this example recording encoded as stereo and binaural. To my ears, the binaural recording is more open and natural. Of course, I had the benefit of hearing the actual environment. Do you hear a difference?

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Is ambisonic audio the same as binaural?

Ambisonics is a unique recording technique that captures audio with four to sixteen channels. It was theoretically conceived by Michael Gerzon​​​​ in the 1970s; however, it wasn’t until recently that Ambisonic recording made practical headway. The beauty of Ambisonics is that it can be decoded mathematically into many formats, including its native Ambix format, surround, stereo, and binaural. So, yes, it’s binaural audio and more!

One significant benefit of Ambisonics over binaural is its rotatable image. When decoded on playback, the sound field of ambisonics shifts as the listener moves their head. Volume changes are also dynamically mapped. Ambisonic is the audio equivalent of a 360 video. Conversely, binaural audio is static and equivalent to the image of a 3D Viewmaster.

360 Degree Video with Embedded Ambisonic AudioNote: Some devices and browsers do not support ambisonic playback.

Personal and Practical Recording Experience

Let’s explore some personal and practical experiences making binaural recordings. I’ve been experimenting and recording binaural audio since the mid-1990s, first with microphones from Sound Professionals and a Sony minidisc recorder. Despite its limitations, that small setup lent itself nicely while on a trip to German. I’m thankful to have captured beerhall ambience at the Hofbräuhaus and a violinist riding the S-Bahn. Even though those experiences happened some time ago, I can still relive them as if they happened just yesterday. It’s impressive how binaural audio can transport you back in time and make you feel like you’re experiencing everything all over again.

[lbg_audio7_html5 settings_id=’7′]Binaural Example – Mini Disc – Germany Mid 1990’s

The benefit of binaural audio is realism. It captures it like nothing else, but binaural recording has challenges. Using a dummy head to record with is bulky and cumbersome. Moreover, be prepared for curious gazes as inquisitive onlookers wonder what you are doing. Some will ask you questions and interrupt your recordings. Of course, this is much less of a problem when recording nature sounds.Using your own head as the acoustic model with a smaller recording setup avoids some of that interaction. However, be mindful that your head remains still while recording; otherwise, image shifts will occur. One practical and modern approach is to stare mindlessly at your phone. You will look less like a psychopath gazing into the distance, and people will assume you’re preoccupied with social media. As an added bonus, you can monitor volume levels if using a recorder with an accompanying phone app, such as the Zoom F3.

Recording gear challenges

In my experience, using quality equipment results in a better recording. However, the tricky challenge here is that binaural microphones are often tiny, with insufficient low-frequency response and high noise levels. These can work in louder environments but yield poor results when recording quiet nature sounds, particularly when coupled with cheap recorders. Even DPA 4060 mics, which some nature recordists use, are too noisy for my taste.

That’s not to discourage you from making your own binaural nature recordings. As photographers say, “The best camera is the one you have with you.” So, I encourage you to use what you have. I keep a cheap Zoom H1n and Roland mics in my car to capture any sounds that come my way, warts and all!

Binaural recording hybrids

Many of the Wild Soundscapes recordings still employ traditional stereo recording techniques, such as ORTF, Spaced Pair, and Mid-Side. Though I’ve strayed away from Mid-Side for nature recording, ORTF remains a favorite and delivers impressive soundstage accuracy. I also may use a spaced pair of mics for a wider soundstage but at the expense of localized accuracy. 

On a side note, reverberant, vibrant atmospheres deliver the most exciting results when recording. The additional interaction of sound bouncing off trees and rock walls really adds depth and space. While this holds true for stereo recording in general, there is an undeniable touch of magic that unfolds when binaural techniques are used.

The Crown SASS and Wildtronics Stereo Ambient Array Microphone are shining examples of pseudo-binaural techniques. The original Crown SASS is too noisy for nature, but recently I modified one to use the new Rycote OM-8 capsules. 

Modified Crown SASS Microphone

Modifying a Crown SASS

This pseudo-binaural setup offers some of the HRTF benefits of binaural with a balanced frequency response and much lower noise. Still, it does not account for sounds on the vertical axis. Yet, it will be my go-to setup once I solve its need for better wind protection. I understand Lang Elliot at  Music of Nature uses a similar arrangement with Sennheiser microphones. Many nature enthusiasts make their own version of the Crown SASS. 

Other pseudo-binaural recording techniques include using a Jecklin disc or an Olson Wing. These, too, are baffled stereo techniques that account for some HRTF of binaural. I’ve been exploring Curt Olson’s “Wing” design and have been impressed with It’s simple and effective design.

A few years ago, I purchased a Rode NT-SF1 ambisonic mic. Truthfully I don’t use it much. While I can decode the recordings to binaural, it lacks the depth I seek. That, coupled with the hassle of managing additional channels and the backend decode, drives my preference to use something else. I am, however, eager to try some Higher Order Ambisonics microphones like the SPC mic from Harpex.

Broken Rode NT-SF1 Ambisonic Microphone

Rode NT-SF1 – Broken Capsule

Plus, the NT-SF1 has some delicate build quality issues.

Binaural Sound Examples

Use the player below to hear examples of binaural recordings. Notice how the environments acoustics play a roll in the envelopment of sound.

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The Binaural wrap up

I hope you understand binaural audio more – its distinctive character, how it contrasts with traditional stereo, and its remarkable ability to capture sound in an incredibly lifelike three-dimensional way. I encourage you to make your own binaural recordings and share them with others. It’s truly a delight to witness the inspired reactions of first-time listeners. And, of course, you can also send them to explore the Wild Soundscapes website!

Please, leave a comment if you’ve learned a little or enjoyed this post.

All the best!

Picture of Jerry Horwath

Jerry Horwath

As a well-seasoned recording engineer who spends a lot of time in dark, windowless rooms, I truly enjoy being outdoors whenever possible. Nature and humor have always been my sources of comfort, so I decided to combine all three. That's how Wild Soundscapes came to be.