How do I take a binaural recording

3D with two channels - binaural stereo recordings

Binaural audio: tutorial, information and equipment

The “other” stereo method - and its advantages and disadvantages

(Image: Shutterstock / mediamix)

Binaural stereo recordings are definitely a trend. This can be seen from the fact that binaural microphones are available from previously unknown and established companies. Basically, binaural stereo is just a recording technique that has been revived. Here you get the most important information to get started with the binaural audio recording technology.

What is "binaural audio"?

As a rule, binaural recordings are nowadays referred to as audio recordings that should be listened to using headphones if possible. This is the case because each of the two ears must only receive the signal intended for this ear for the stereo process to function correctly. Binaural audio can also be mimicked with software.

What is the difference between binaural stereo and “normal” stereo?

Headphones should be used for listening. The location works not only left-right, but also top-bottom and left-right. The recording takes place with only two microphones, which are installed either in the real ears or as lifelike as possible reproduced auricles.

No, that's not a wrong picture: this is a stereo microphone for binaural recordings!

What is the difference between binaural stereo and surround and 3D / immersive audio?

Binaural stereo requires only two channels from recording to playback and does not have to be further encoded or decoded. Multi-channel audio formats have actual sound sources that often allow better localization. Surround and 3D / Immersive audio are designed for loudspeaker playback. Multi-channel formats work regardless of the head and ear anatomy of the listener. Multi-channel recordings can be made with the Zylia Portable Recording Studio or the Zoom H3-VR, for example. There are also manufacturers who do not start with “Z” who offer multi-channel recording systems. ;-)

Such a microphone array is NOT necessary with binaural audio to get a 3D impression. Two microphones are enough.

Is binaural audio a new development?

No, binaural recordings have been around for a long time. The foundations were laid in the century before last, artificial head recordings became popular for a short time in the 1970s. Now that binaural recording has only had a niche existence in audio production, it is currently becoming increasingly popular.

Why is binaural audio becoming a trend?

The spread of headphones continues to grow. With the advent of practical wireless in-ears such as the Apple AirPods Pro, the consumption of music, but also voice productions such as podcasts, radio plays and audio books is increasing. It has become cheaper and easier to make recordings yourself, even as a layperson.

What is binaural stereo good for?

Binaural recordings and binaural playback are useful wherever good localization in space and immersion are required - and where it is assumed that headphones are primarily used for listening.

Typical areas of application:

  • Radio plays
  • Atmos
  • 3D / gaming
  • Music productions in which spatial impression is important (classical, especially organ productions)
  • Audio demonstrations / training on auditory perception
  • Music productions (or individual tracks from them) that are likely to be consumed to a large extent via headphones

Tip: Make binaural recordings in the rehearsal room - Reason: The auditory memory of the situation is the best possible, as you can literally hear what you have recorded with your own ears! This is particularly interesting as a drummer (even if it can hardly be used professionally).

What do you need to record binaural audio?

  • Either an artificial head (Neumann KU 100) or microphones that are attached to or in the ears or to a "dummy" can be used as a binaural microphone.
  • Stereo recording device, e.g. stereo digital recorder
  • Headphones for eavesdropping

Hack 1:

The dummy head for binaural recording can also be modeled yourself, for example from plaster, wood or other material. The better the auricles are represented, the better for the function with in-ears. The microphones should be located roughly at the outer end of the ear canal (not where the human eardrum is located, because then the ear canal with its important acoustically effective dimensions would be doubled!). Pressure receivers should be used because the human ear also registers pressure differences and not the pressure gradients. The correct dimensions (ear spacing) and the presence of cheeks / eye sockets and especially the nose are important when modeling!

Hack 2:

Alternative to the binaural microphone you bought: There is a super cheap version that my old buddy Daniel discovered by chance in the early 1990s and with which he made numerous recordings: He had an MD recorder that also had a 3.5 “Microphone input and which was next to the headphone jack. Because typical in-ears work according to the dynamic converter principle, they can also be used as microphones (albeit with incorrect impedances). Turning the in-ears around in your ear and connecting them to the microphone input can therefore work, for example with a digital mobile recorder.

Complete recording and monitoring system for binaural stereo: The wireless Hooke Verse - installed on a "real" head.

What do you have to pay attention to when creating binaural recordings?

  • The pre-location is usually pretty bad. For humans, however, this does not have to be particularly good, because for this area there is a more suitable, much more precise angle-representing sense: the sense of sight.
  • For microphones that are placed in the ears: Every movement of the head, even vertically, moves the entire stereo / 3D image.
  • Noise from breathing, clothing, heartbeat, swallowing, etc. can be transmitted to the microphones, so stay as quiet as possible.
  • The best results are achieved with "standard anatomies", that is, in people with not noticeably special head and especially auricular dimensions and shapes of the outer ear.
  • The microphone diaphragm should be at the entrance or outer edge of the eardrum.
  • With binaural ear microphones, monitoring is only possible by another person. Therefore, the level must be kept in view with the meter.
  • Since pressure receivers are usually used, attention should be paid to infrasound and sub-bass. If in doubt, use a high-pass filter!

How does the location of sound not only work left-right, but also front-back and top-bottom with binaural recording and playback processes?

The human location of sound events (also called "localization") works on three different levels:

  • Horizontal plane: Left-right location
  • Frontal plane: Front-back location
  • Median plane: Top-bottom location (also "elevation")

The Horizontal plane is the one used for normal stereo listening through speakers and headphones. Signals are displayed either with a stereo microphone method, a pan control or other positioning method. The location in the horizontal plane works with a combination of transit time differences between the ears due to slightly different sound events as well as differences in timbre resulting from the shadowing by the head. In very simplified terms, the location works in the Frontal and median planes through the characteristic frequency response and phase changes that take place especially through the sound detours in the windings and channels of the pinna (= outer ear).

How does binaural audio sound?

Here are examples of binaural recordings (listen with headphones!):

Does binaural audio work well? What are the sonic disadvantages of binaural recordings?

There is a fundamental, systemic disadvantage: The so-called HRTF (Head Related Transfer Functions) are basically the filter responses of the entire head to incoming sound. Depending on the direction of incidence in the three levels, the pattern is different and can be evaluated. However, these HRTFs differ from person to person because everyone has a different anatomy. And because everyone has learned directional hearing with their own anatomy, the localization of sound events with "strange heads", for example artificial heads or other people who have recorded their ears with microphones, works significantly worse. There are even studies showing that people who, for example, have had a nose operation performed or who have lost parts of their ears in an accident, are initially much more difficult to localize. Further problems arise from the weak prelocation and, of course, from the rather poor compatibility with loudspeaker reproduction.

Advantages of binaural recordings

  • 3D impression / immersion
  • only two channels required for recording and playback
  • Inexpensive technology, partially feasible with existing / self-made technology
  • amazingly natural, “real” localization possibility

Disadvantages of binaural recordings

  • only suitable for headphone playback
  • Prelocation weak
  • Results vary depending on the admission requirements and individual anatomy
  • with binaural recording in "real" ears problems caused by movement, intrinsic noises, etc.

Reviews of equipment for binaural recordings

What are "binaural beats" and how do they work?

Binaural beats have nothing to do with the recording and playback technology shown here. Binaural beats are low-frequency sound impressions that our sense of hearing produces when audio signals that are slightly out of tune are applied to the ears. This is comparable to the emergence of a beat, as we know it when setting the choir purity of pianos or other multi-/ double-stringed string instruments - only that these signal sensations only arise in the brain. Binaural beats can be used in neurology and for relaxation.