Audio Sound Fields and Imaging

Both the nature of the sound field and the intended playback medium have to be considered when choosing the optimum recording setup. Just aiming a microphone at a sound source will usually lead to disappointing results.

Sound fields

A sound field is the area from which sounds we wish to record are coming. It's normally described as an angle with the nominal centre of the microphone array at the apex, and most often for studio and concert hall we only consider the horizontal plane, as this is what contributes mainly to the stereo image of the finished recording. But in the wild the vertical plane is also important - particularly in the upward direction. As there is no ceiling, unwanted sounds from above need to be considered.


Imaging is the recording and reproduction of a sound field that attempts to synthesise the spatial experience of a listener to the original sound source. From the inception of recording at the end of the 19th century, the only way to reproduce the sound was mono - a single loudspeaker from which all the sound captured by a single microphone emerged. This was considered adequate for over half a century, but by the mid 1930s engineers were experimenting with techniques to improve the realism of the listener experience - aiming to achieve some sense of being present in front of the performance. By the 1950s the public had begun to develop higher expectations than mono could provide. Indeed it was described at that time by pioneering sound engineer G.A. Briggs as "listening to a concert through a hole in a wall". Dissatisfaction with this effect led to the development of the stereo reproduction technique we are most familiar with - the use of two or more microphones to create multiple channels fed to a bank of loudspeakers for reproduction. As early as 1951 experiments in commercial stereo reproduction were taking place [see Briggs, G. A., Sound Reproduction, 3rd Edition, Wharfdale Wireless Works 1953], including some in multichannel precursors to surround sound. It was observed that substantially poorer frequency response was tolerable in stereo than in mono, which allowed cheaper reproduction systems to satisfy a wide audience. These days we can easily obtain equipment with the benefits of stereo imaging and a frequency response covering the whole audible range, so we get the best of both worlds.

Stereo really came into its own in the late 1960s as the familiar two-channel system we now use. With the introduction of the Compact Disc a decade later, two-channel became the de facto standard for sound reproduction. Subsequently, several more elaborate techniques - broadly described as surround sound and primarily driven by the demands of the movie industry - have been developed in an attempt to provide more "immersive" imaging by use of more channels, putting the listener in the centre rather than at the edge of the sound field.

We tend to think of sound fields primarily in the horizontal plane, as that is what mostly interests us for stereo reproduction of music and speech - indeed even surround sound only occasionally makes use of loudspeakers above or below the listening position. But ordinary commercial microphones have much the same pickup pattern in both the vertical and horizontal planes. The pickup pattern is a solid cone rather than "vertical" or "horizontal". In the studio, and even in a concert hall, this is not usually a significant issue, but for the wild soundscape recordist quite a lot of uncontrolled sound sources may be overhead, so it's important to take account of them in the field.