Multichannel Microphone Array Design
Multichannel Microphone Array Design
复制标题
多通道麦克风阵列设计
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
G. Dû
中科院分区：
文献类型：
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作者：
Michael Williams;G. Dû
The design of a microphone array for multichannel sound recording involves the manipulation of many interrelated parameters : Segment Coverage, Electronic Time and Intensity Offset, Microphone Position Offset. This paper discusses the options available to the sound engineer in the choice of segment coverage by the Front Triplet and Back Pair, and how Critical Linking can be obtained in relation to the Lateral Segments. A basic design procedure is illustrated that will enable the sound recording engineer to design the microphone array neededfor a specific reproduction configuration. Introduction The basic parameters of a Multichannel Microphone Array were presented at the 107th AES Convention in New York in a paper (2) entitled Microphone Array Analysis for Multichannel Sound Recording (preprint 4997). Parameters such as Segment Coverage, Electronic Time and Intensity Offset, Microphone Position Offset were defined, and their influence on the design of a microphone array was discussed. However the design of a specific microphone array to meet the needs of a particular sound recording environment was beyond the scope of this first paper. This present paper tries to meet to some extent the needs of an individual sound engineer to be able to design a microphone array taking into account the particular musical and acoustic environment for a specific recording. Each stage in the design procedure is discussed : Front Triplet Coverage The reproduction of this front sound stage is probably the Lost important stage in the design of a specific Multichannel Microphone Array (MMA) design. In general the direct sound from most sound sources encountered will be covered by this front triplet, however the configuration of the three microphones will also condition considerably the difficulties encountered in obtaining critical linking with the lateral and back segments. l Back Pair Coverage This is usually dependant on the musical sound source configuration. Is the sound source completely surrounding the microphone array or is the disposition more traditional? In the second case however, the coverage should be chosen in relation to the particular acoustic environment, the artistic choice of the sound engineer will also influence the type of envelopment that he considers necessary in the back reproduction segment. AES 108th CONVENTION, PARIS, 2000 FEBRUARY 19-22 WILLIAMS AND LE DU PREPRINT 5157 MULTICHANNEL MICROPHONE ARRAY DESIGN better than the traditional stereophonic reproduction. However the front perception zone of reproduction of about 60” seems to satisfy approximately our needs as to the angular size of the main sound stage, but with multichannel continuous sound field recording and reproduction, we have the freedom to be able to widen this sound stage if we feel the need. A multichannel surround sound reproduction system is also capable of reproducing realistically the multitude of early reflections and the surrounding reverberation, which are mainly responsible for the feeling of (( space D in a good recording. So great care must be taken in the positioning of the sound source and the microphone array, in relation to the acoustic environment, to exploit this effect to a maximum. The approach is obviously different in the the case of a completely surrounding sound source, either where one needs to record the natural sound environment of, say, a forest, or in the case of a certain number of musical works written specifically with a view to creating a surround sound environment. The microphone system is then, by definition, placed in the middle of the surrounding sound source. In this type of situation the smooth reproduction of the sound field means that each sound reproduction segment covered by a pair of loudspeakers must correspond exactly to the same segment of the original sound field. But the realistic reproduction of sound perspective depends entirely on our ability to place each sound source at the required distance from the microphone system. This means unfortunately that we must accept as inevitable the distortion of perspective in the recording of the natural outdoor sound environments fortunately the perception of the exact distance of this type of sound source is rarely critical. Front Triplet Design The choice of the Front Triplet Coverage Angle is determined basically by the position of the microphone system, and the angular width of the sound source as “seen” by the microphone array much the same as with a two channel stereophonic microphone array. However we have a degree more liberty in the choice of the coverage angle than was the case in stereo. The coverage angle can either be within the angle occupied by the sound source, in which case it is the lateral segments that will reproduce the extremities of the sound source, or as with stereo, the coverage angle can be greater than the angle covered by the sound source the reproduction of the direct sound from the source then being within the two front segments. The limit case in which the coverage angle is equal to the sound source angle is of course also possible but does not suffer from that claustrophobic impression often given in stereophonic recordings when not enough attention has been paid to producing a certain quantity of (( side-room D. Side-room can be considered as the “space” left in between the extremities of the reproded main sound stage and the limits to the possible stereophonic image created by the position of the loudspeakers. This is very similar to the headroom that is necessary for good balance in a picture. AES 108th CONVENTION, PARIS, 2000 FEBRUARY 19-22 3 WILLIAMS AND LE DU PREPRINT 5157 MULTICHANNEL MICROPHONE ARRAY DESIGN The abrupt limit to the sound field of stereophonic reproduction is not perceived in a multichannel reproduction system due to the continuation of sound field reproduction, obtained on condition that the lateral segments are Critically Linked to the Front Triplet Coverage. The (( side-room D in a multichannel system is no longer necessary as we have all the room that we need ! We have therefore three choices possible for the the Front Coverage Angle : a) Front Coverage Angle > Angle of the Sound Source in which case the sound source will be reproduced within the sound stage generated by the front three loudspeakers b) Front Coverage Angle = Angle of the Sound Source in this case the sound source will fill the whole of the front sound stage c) Front Coverage Angle < Angle of the Sound Source in this case we will need the lateral segments to continue the reproduction of the sound source in the left and right lateral segments, generated by the left front & left back loudspeakers, and right front & right back loudspeakers respectively. Once we have determined which choice to make for the Front Coverage Angle and knowing the position of the microphone system we will be able to consider the actual combinations of distance and angle between the microphones that we need to adopt. We will consider two specific examples of Coverage Angle. Table 1 : where the Front Triplet has a total Coverage Angle of 120°. This means that both the Left Front Pair and the Right Front Pair must cover an angle of 60” each Table 2 : where the Front Triplet has a total Coverage Angle of llO”. This means that both the Left Front Pair and the Right Front Pair must cover an angle of 50” each.
