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What is Binaural Recording? – Cool 3D Sounds!

Have you ever heard of three-dimensional sound recordings? Well, it may come as a surprise to you, but these types of audio recordings have even been used commercially. This concept may not seem all that important to the average consumer. However, if you are seriously into audio engineering, you need to ask – What is Binaural Recording?

In my personal experience, I have not heard the subject of today’s article being discussed a lot among audio practitioners. I guess this is understandable, since 3D sounds are rarely used in conventional music production. I will briefly explain to you the principles behind this recording method, and how it affects listeners. Let us start learning!

Chris Milk

Chris Milk’s binaural audio recording instrument / Photo by A74ir89 / CC BY-SA 4.0

Introduction – 3D? Sounds Cool!

Essentially, binaural recording is a sound recording method that uses two microphones, positioned in a way that creates a 3-D stereo sound experience for listeners, akin to being in the room with the performers. This effect is typically achieved by using a technique called “dummy head recording”, where a mannequin head is outfitted with a microphone in each ear.

Binaural audio recordings are only suitable for playback through headphones and will not translate correctly over stereo speakers. The concept of 3D or “internal” form of sound has also influenced many useful advances in audio technology such as stethoscopes creating “in-head” acoustics and IMAX movies being able to produce a three dimensional acoustic experience.

This is unlike stereo recordings, where the natural ear spacing of the head and ears is not considered. This factor naturally occurs as a person listens, generating their own ITDs (interaural time differences) and ILDs (interaural level differences). Since conventional stereo produces “loudspeaker-crosstalk” which interferes with binaural reproduction, headphones are used instead.

ITD

ITD (Interaural Time Difference) between right ear (top graph) and left ear (bottom graph). Sound source: white noise with 100 ms duration from left (90° azimuth 0° elevation)

A pinna-less dummy head may be ideal for quasi-binaural recordings, that are intended for listening through conventional stereo systems. The basic principle behind true binaural sound, is that an audio recording and reproduction system chain, from microphone to listener’s brain, should contain only one set of pinnae (preferably the listener’s own) and one head-shadow.

Here are some other topics that we’ll be looking at:

  • Recording techniques
  • Playback requirements
  • Frequency response
  • Common uses

Recording Techniques

The most simple recording practice includes two microphones that are placed 18 cm apart facing away from each other. This technique will not produce a true binaural recording, but the distance and position roughly represents the position of an average human’s ear canals. More elaborate techniques however, requires specialized recording equipment.

Neumann K100

Neumann Ku 100 (microphones are inside the dummy head, pointing towards the ears) / Photo by EJ Posselius / CC BY-SA 2.0

A complete binaural recording unit consists of a dummy head with two high-fidelity microphones mounted inside, that has inset ear-shaped molds to capture all of the audio frequency attenuation that happens naturally as sound wraps around the human head and is “shaped” by the form of the outer and inner ear. The Neumann KU-81, and KU-100 are the most well known binaural recording sets.

You can also use microphones with a separating element between them (such as the Jecklin Disk microphone technique), in order to produce a stripped down version of binaural recordings. Do take note that by using this method, not all physical information required for exact localization of the sound sources are preserved, but it is more suitable for loudspeaker reproduction.

Playback Requirements

The effect of binaural recordings can be faithfully reproduced through headphones or a dipole stereo. Mono playback and stereo loudspeaker systems do not support binaural recordings, as the acoustics of these systems distorts the channel separation due to crosstalk (this can be remedied by carefully designing the listening environment to include expensive crosstalk cancellation equipment).

Bone conduction earphones

Open-ear headphones (also known as bone conduction headphones) / Photo by Ksfan / CC BY-SA 3.0

Even consumers who are just using a cheap set of headphones can enjoy binaural recordings. There are also several manufacturers that have produced units that are specially engineered for binaural playbacks. However, these in-ear-canal phones usually have poor externalization (inside-head localization) and even normal headphones suffer from this, especially if it completely blocks the ear from outside.

Through experiments, it has been found that open-ear headphones are more suitable, where the drivers are sitting in front of the pinnae with the ear canal being “opened” to the air. The general opinion is that when the ear canal is completely blocked, the radiation impedance seen from the eardrum to the outside will change, which negatively affects externalization.

Frequency Response

During natural hearing, there tends to be a boost from 2kHz to 5kHz. Since headphones are very near to the ears, they actually nullify this natural frequency response by the head and ear. Hence, most headphones are designed to produce the 2kHz to 5kHz frequency boost, which reflects natural hearing. Even the so-called “high quality” headphones have this same boost of frequencies.

Headphone Amplifier

A Beyerdynamic DT 770 PRO with a FiiO headphone amplifier / Photo by MMuzammils / CC BY-SA 3.0

For binaural listening however, headphones require a flat frequency response to the ear-canal entrance (not eardrum), since the recording microphones are originally placed at the ear-canal entrance. Although it is theoretically possible to equalize headphones for a flat response at the entrance, an ideal solution is to use headphones designed without the boost in the first place.

Most people are not aware of the 2 kHz to 5 kHz boost that most headphones have, and this may have led to an inaccurate assessment of binaural recordings, since flat headphones are not common. If headphones have a flat frequency response, and used with headphone amplifiers that have equalizers, then there could be a more controlled listening experience, whether in binaural or stereo mode.

Common Uses

Binaural recordings are rarely used in commercial audio productions, due to the high cost of specialized equipment required to produce high quality recordings. Also, the types of sounds that can be recorded in the studio do not typically have a high market value. It is mainly used for live orchestral performances, and ambient “environmental” recordings of nature, city sounds, and other similar subject matters.

That’s all I have for you folks today. Are you ready to incorporate binaural recordings into your projects? Well, at the very least, I hope that you are now more familiar to the principles behind it.

Do leave comments or questions below, and share this article with your friends!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

8 Comments

  1. Oh my gosh! I’ve heard of these! Dummy-head mics are SUPER popular in Japan. Well…not with regular folk going to the music store, but the commercial use of binaural recording equipment is pretty well-received. I want to say it picked up over there, somewhere around 2012 and has been gaining speed ever since.

    I’m already an audiophile to begin with, but seeing the mechanics of how 3D recording works is pretty insane. I can attest that open-ear headphones work better than the in-ear ones. That also depends on the nature of the recording:

    For instance, 3d recording in Japan often gets used for recording drama CDs: think of an audiobook with an all-star cast recording a movie or voice-over; while the listener is the main character. lol It’s weird, but a pretty awesome experience. The more action-packed dramas can be pretty disorienting. I think the more chill stories or moments highlight the 3D effects the best (e.g., footsteps coming towards from the opposite direction, etc.).

    Sometimes it feels like sitting in a play, but your both the audience AND the participant. This newer, binaural way of recording really changed a chunk of the entertainment industry in Japan, I think, and is still doing pretty good actually.

    • Hey there!

      Wow, I didn’t know that binaural recording is a huge thing in Japan’s entertainment industry. Must be cool to have these sounds heavily incorporated into dramas and TV shows. Thanks for the information!

      Cheers =)

  2. Hey Farhan! Great post, I learnt something very interesting today, I didn’t know such a thing like 3d sounds existed, do you have some examples of a 3d sound? like a song or a movie, I would like to check it out and compare it to a normal sound, thanks for sharing have a good one.

  3. I have never even heard of binaural recording before! I would love to hear something made through binaural recording and see how it compares to other types, because I bet it sounds amazing!
    Do they use it a lot in movies or tv shows? Or is it still relatively a new thing?

    • Hi there!

      Binaural recordings are really cool, and you might like it more than conventional stereo mixes. I don’t work in the film industry, therefore I do not know if they actually apply binaural recordings in film productions. Movie theatres uses surround sound systems (using speakers), which is not ideal for binaural audio reproduction. Hence, I’m assuming that there is currently no practical use for binaural sounds in movies (well, at least not at the moment).

      Thanks for dropping by!

  4. I like to listen to binaural music when I am studying or working, mostly from YouTube. I have no idea if these are “true” binaural recordings or inferior. Basically if it helps me to relax and focus, I’m happy.

    Some of the recordings include a combination of Isochronic tones and binaural beats that I find quite soothing.

    I have no idea what Isochronic tones do or how they are created. I go by what is an enjoyable background listening experience that does not distract me, but rather enhances, what I am working on.

    You have a wonderful site. Although the technical side of audio recording is not my area of knowledge, I am interested in the effects that sound waves have in healing and learning. I enjoyed visiting your site.

    ~Jude .

    ~Jude

    • Hey Jude!

      I have to say that binaural recordings are hard to discern for the inexperienced listener. It is very different from the more conventional stereo recordings that you hear in pop music. The best way to improve your hearing, is to search for sound that is produced using binaural recording, and then comparing it to other sounds. Here’s a great clip you should watch!

      Since you are interested in the effects that sound has to our brain, I strongly recommend you read this article. Thanks a lot for your thoughts and kind compliments. Do keep in touch!

      Cheers!

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