The 背景 声音 of an 环境 in 关系 to which all foreground 声音 are 听 such as the 'silence' of an empty 房间 conversation in a restaurant or the stillness of a forest 氛围 is actually comprised of many small 声音 near and far which 通常 are 听 as a composite 不 个别 Also called 周围 噪音 源 Barry Truax - Handbook for Acoustic 生态学 CD-ROM Edition Cambridge Street 出版 1999 - CSR-CDR 9901