What does binaural mean? Definition and examples

At its simplest, as a combination of the Latin bini (“twofold” or “two apiece”) and aural (“pertaining to both ears”), ‘binaural’ means ‘relating to or involving both ears’. The word seems to have been coined in 1861, by Somerville Scott Alison – the inventor of a binaural version of the previously monaural stethoscope.

Being able to hear binaurally – with both ears – confers multiple benefits upon an organism, including:

• The ability to isolate specific sounds
• Improved hearing in noisy environments 
• Directional hearing, allowing the sources of sounds to be located (localization)
• Stronger spatial awareness and balance.

Binaural hearing also allows the brain “to form a clearer and more complete soundscape” than it would if only receiving input from one ear. This is because the brainstem nuclei can make judgments about, say, where a sound is coming from by contrasting differences between the moment at which the two ears receive the same sound, and between the two ears’ perception of a sound’s volume.

In terms of sound recording, a binaural approach seeks to replicate these ways in which we ourselves hear: as an immersive, three-dimensional experience.

Binaural audio was invented in 1881, by inventor and engineer Clément Ader, a pioneer of telephony. A system later known as the Théâtrophone transmitted audio from the Palais Garnier opera house, Paris, to listeners two miles away, before being rolled out to theaters across Europe. At this time, amplifiers had not yet been developed, meaning that electrical audio signals could only be listened to via a telephone receiver earpiece; as such, until the middle of the 1920s, all radios were listened to with headphones. Moving-coil loudspeakers pushed binaural audio into relative obscurity, until its revival by the increased prevalence of personal headphones.

To mimic human hearing, binaural recording attempts to replicate the conditions in which it occurs. “A pair of microphones [spaced] a heads-width apart” will go some way to doing this. Two options are: using in-ear microphones which record exactly what the wearer is hearing, or using a dummy head with a microphone located in each ear. 

Though the first dummy head for binaural recordings (‘Oscar’) was made by Bell Labs in 1933. Depending on the model, modern dummy heads may even include replica ear canals and the external structure of the ear. (Alternatively, you can even make your own binaural dummy head.)

By having sound waves bounce off of the same planes and angles encountered when they enter our ears, recordings made with both of these techniques will capture the experience of human hearing. This includes taking into account ‘head shadow’, a term for the way that the head itself acts as an acoustic barrier.

In order to experience binaural recordings as a listener, it’s necessary to use headphones, as, by “maintain[ing] that same isolation between the left and right channels”, these emulate real-world hearing; each of the dual recordings are transmitted to just one ear. This preserves inter-aural differences of time and level – a sensation which would be lost if binaural recordings were played over conventional speakers. 

Binaural audio isn’t to be confused with surround sound (patented in 1931) – but this is easier said than done; even Alexander Graham Bell, who patented the first practical telephone, conflated the terms, and, in the 1950s, the recording industry used the word ‘binaural’ as a synonym for ‘stereo’. While surround sound continues to be most appropriate for, say, the cinema experience, it seems likely that, “as video game and VR developers push for greater immersion sonically as well as graphically”, binaural recording will continue to gain prevalence in those fields. 

Binaural audio has also gained popularity among the creators of ASMR (autonomous sensory meridian response) stimuli, which are intended to provoke a tingling or goosebumps-like sensation in the listener, or even euphoria. ASMR may be connected to binaural beats: an auditory illusion created when a listener hears two tones of a different frequency, one in each ear, which causes the brain to create an additional tone: a binaural beat.

---

Featured photo by Susan Wilkinson on Unsplash