Chapter 21 - Audio 3D - Binaural recording and binaural playback techniques

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The aim of binaural techniques is to reproduce sound exactly as it is perceived by a listener. For recording a fake head is used, which has two microphones placed where the ear-drums would be. The head's characteristics are replicated in detail, the microphones are placed at the end of a conduit simulating the ear canal. This way the interference between the two recorded sounds is fully eliminated. Moreover, the simulation of the ear canal allows us to simulate exactly the frequency loss a sound undergoes when it enters the human ear. Even the auricle and the Eustachian tube [Human ear ] are reproduced with great attention to detail.

The listening experience of these recordings should take place wearing ear-phones in order to keep the simulation real. The same reproduction through a pair of loudspeakers would be ineffective due to the considerable interferences between the two signals. Also these techniques have gone through quite a big evolution, allowing even listenings with correctly placed diffusers.

21.6.1. Binaural recording techniques

The Holophonic (1983) binaural recording system devised by Hugo Zuccarelli adopts this kind of approach.

Other techniques were then developed by several people (Umberto Maggi, Dallas Simpson, Aachen Head) and companies such as Neumann who developed a sophisticated dummy head called Neumann KU-100 and showed in the picture below. Its main characteristics are a psychodinamic equalization stage and a perfect reproduction of the pinna.

3D Audio - Dummy head Neumann KU-100 for binaural recordings

Dummy head Neumann KU-100 for binaural recordings

It's worthwhile mentioning some of the recordings on Pink Floyd's album "The Final Cut" where these techniques are used. Even more surprisingly, the song "Alan's Psychadelic Breakfast" from the album "Atom Heart Mother", again by Pink Floyd, sounds like it was recorded using this technique, whereas in actual fact it was recorded well before this technique existed, in 1970, which says a lot about Pink Floyd's masterful ability in manipulating sound.

Let's now listen carefully at an example of binaural recording for which we recommend using your favourite headphones.

The example is courtesy of Franco Russo aka Franko. Check out for more Franko's recordings at www.terzoorecchio.com .

The following is a recording of a pressed piece of paper moving around the head.

Paper experiment 3D - 00:54  [Track 70]

3D Audio - Paper experiment 3D - 00:54 [Track 70]


21.6.2. Binaural reproduction techniques

These techniques allow us, even when the initial signal is mono, to obtain a stereo signal where the sound field extension can be widened or narrowed at will.

The following sound illustrates an application of this kind of algorithm. Starting from a mono sound, the image progressively widens until it reaches its maximum stereophonic breadth. Then it narrows back down until it reaches its initial mono shape.

Transformation of a mono sound into a stereo sound  [Track 71]

3D Audio - Transformation of a mono sound into a stereo sound [Track 71]