Transaural Stereo is a technology suite of

analog circuits Analogue electronics () are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels. The term ''analogue'' describes the proportional relationship between a signal ...

and digital signal processing algorithms related to the field of sound playback for audio communication and entertainment. It is based on the concept of

crosstalk In electronics, crosstalk (XT) is a phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, ...

cancellation but in some versions can embody other processes such as binaural synthesis and equalization. The technology was developed in the 1970's by Duane H. Cooper and Jerald L. Bauck.

Description

The central concept behind transaural stereo is that there are two

loudspeakers A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

and a single listener (two ears). The left-channel signal should only reach the left ear and the right-channel signal should only reach the right ear, each with appropriate

timbral In music, timbre (), also known as tone color or tone quality (from psychoacoustics), is the perceived sound of a musical note, sound or tone. Timbre distinguishes sounds according to their source, such as choir voices and musical instruments. ...

corrections. To effect this, a circuit or

computer algorithm In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algo ...

is devised. It is based on the knowledge of the four frequency-dependent transfer functions, the so-called

ipsilateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

contralateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

paths.: * L-to-L * L-to-R * R-to-L * R-to-R These four functions are examples of

head-related transfer function A head-related transfer function (HRTF) is a response that characterizes how an ear receives a sound from a point in space. As sound strikes the listener, the size and shape of the head, ears, ear canal, density of the head, size and shape of n ...

s (HRTF). A more general theory allows arbitrary numbers of loudspeakers and ears (listeners). The inputs to the process are sometimes recorded binaural signals from a recording mannequin ("dummy head") but this is not a requirement. Virtual loudspeakers can be formed by combining crosstalk cancellation with binaural image synthesis so that, for example, narrowly-spaced loudspeakers can be made to sound farther apart or a five-channel surround sound system can be made with only two actual loudspeakers, a virtual home theater.

History

transaural stereo was developed by Duane H. Cooper and Jerald L. Bauck. An early version was published as a Master's thesis at the

University of Illinois The University of Illinois Urbana-Champaign (UIUC, U of I, Illinois, or University of Illinois) is a public university, public land-grant university, land-grant research university in the Champaign–Urbana metropolitan area, Illinois, United ...

in 1978 and later in the ''

Journal of the Audio Engineering Society The Audio Engineering Society (AES) is a professional body for engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products ...

''. The work was continued in the mid-1980s as an improvement on and practical implementation of the early work in comparative auditoria studies in the 1960s of Schroeder and Atal which was reported as obtaining unstable images under slight head movements. Cooper and Bauck, using methods to stabilize images and reduce the filter count, made an analog crosstalk canceller, a two-speaker spreader, and an eight-position binaural image synthesizer which doubled as a binaural pan pot in 1987–1989 using

biquadratic In algebra, a quartic function is a function of the form :f(x)=ax^4+bx^3+cx^2+dx+e, where ''a'' is nonzero, which is defined by a polynomial of degree four, called a quartic polynomial. A ''quartic equation'', or equation of the fourth deg ...

analog filters in shuffler configurations. Later implementations used highly efficient digital biquadratic filters. The distributed source concept with both discrete and continuous source distributions was created in March 1997 and later refined and the refinement named Optimal Source Distribution.

References

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External links

Transaural Stereo
Stereophonic sound Music technology