Stereo Microphone Techniques: Are the Purists Wrong?
Now that most of the technical aspects of sound recording and reproduction have reached an advanced state it is my contention that the quality of the source material has become the major limiting factor. For acoustically-derived musical performances the microphone technique used to capture the event stereophonically has a profound influence on the attributes of the reproduced sound. I believe that spaced-microphone recording techniques are fundamentally flawed although highly-regarded in some quarters, and that coincident-microphone recordings are the correct way to go. The 'air' and 'ambience' and 'depth' so valued in spaced-microphone recordings are shown to be largely the artifacts of phasiness due to the microphone spacing and not acoustic ambience at all. To support my claims I first define my terms and then review briefly the historical emergence of these two techniques in the 1930's, together with the relevant aspects of stereophonic imaging theory. A series of simple experiments is described which it is hoped the reader will use to demonstrate to his own satisfaction certain basic properties of stereophonic systems. Conclusions are drawn regarding the different characteristics of spaced-microphone and coincident-microphone recordings and a plea is made for more critical and knowledgeable evaluation. It is pointed out that stereophony is inherently incapable of fully natural imaging, and that the Ambisonic surround sound system is the proper extension to multi-channel reproduction. The paper is deliberately non-mathematical in the hope that it will provoke lively thought, discussion and experimentation amongst those engaged in sound recording.
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