So what is Kunstkopf stereophony? Put simply, it is a 3D audio recording technology that enables listeners to relocate all recorded sound sources in space as if they were in the original recording situation. The technology uses two microphones that are usually situated in the ears of a mannequin: this is why the technique is often called “dummy head recording”. The technique “exploits” basic principles of human spatial hearing: very small frequency adjustments that occur when sound wraps around the human head and is transformed by the outer and inner ear. The human brain uses these tiny differences between the two ear/microphone signals (and other, e.g. visual cues) to locate sound in space. For playback, listeners rely on (good) head phones, one of the short comings of this technology as normal loudspeaker playback does not give you the acoustic cues for spatial sound localization. Listening to binaural recordings with head phones is (sometimes) a really  amazing experience – I will come back to this point in another post.

Dummy head recording has a long (pre-)history that dates back to the late 19th century: Clement Ader’s theatrophone was e.g. an archaic binaural broadcasting system. In the 1920s and 30s, different groups in the US and Europe experimented with binaural recording: e.g. engineers at Bell labs built an artificial head named “Oscar”. Originally, Oscar had been designed as a test instrument for the improvement of telephone technology, but the team around Harvey Fletcher also used Oscar for some music recordings.

Mannequin for studying the role of head shape (De Boer & Vermeulen 1939).

Mannequin for studying the influence of the head shape on sound recording quality (De Boer & Vermeulen 1939).

Roughly at the same time engineers (De Boer and Vermeulen) at the Dutch Philips laboratory constructed an artificial head to be used as a kind of binaural hearing aid. De Boer and Vermeulen also coined the term “Kunstkopf”. However, dummy head recordings were not successful for a long time.

One problem for building a working dummy head was that some principles of human spatial hearing were still not understood: e.g. the role of the outer ear. Then, in the late 1960s three German engineers (Henning Wilkens, Georg Plenge und Ralf Kürer) at the Berlin Heinrich Hertz institute designed several dummy heads to be used for an objective comparison of room acoustics of concert halls. But soon they realized that they had built a sufficiently working microphone for 3D sound recordings. Together with the German microphone company Neumann they constructed the first binaural microphone: the KU80, which became the first commercially available dummy head for binaural recordings. Radio makers from the Berlin broadcasting station RIAS used a KU80 for the first binaural radio play Demolition (based on the novel The Demolished Man by Alfred Bester). “Demolition” was presented at the Berlin radio fair in 1973 and many contemporary listeners (experts and normal radio listeners) were convinced that the future of radio would be three dimensional. However, as we all now today, radio did not conquer the third dimension, not least because of many technical and cultural problems with binaural recording. I will blog more about these problems in the future.

Further reading:

As introduction to binaural recording you can take a look at John Sunier, The Story of Stereo, 1881- (1960).

For a more recent account of the history of binaural recording see Stephan Paul, Binaural Recording Technology: A Historical Review and Possible Future Developments (2009).

In the English wikipedia article “binaural recording” you can find two informative binaural audio examples.

The principle of the Neumann KU80 is explained in Stephan Peus, Natural Listening with a Dummy Head (1985), or take a look at the original 1975 brochure of the KU80.

Advertisements