拍（音） are a 形（曲）式 of 振幅 调制 As two 频率 are brought closer together the 拍（音） will gradually slow down and disappear when they become identical If two 音 are about 15 Hz(he zi)/赫兹 or less apart interference will result from their 类似 though 不 exactly identical 频率 Gradually they will move out of 相位 until at 180° 毁/破坏 interference results producing diminished 响度 When they move back into 相位 constructive interference will produce 增 响度 拍（音） arising from the mistuned unison are called first-order 拍（音） and are both an acoustic and psychoacoustic 现象 拍（音） also may be 听 between 纯 音 that are nearly an 倍频程（八度） fifth or fourth apart These are called secondary or second-order 拍（音） 源 Barry Truax - Handbook for Acoustic 生态学 CD-ROM Edition Cambridge Street 出版 1999 - CSR-CDR 9901