If a 声波 is a 复杂 of many 音 of 各种各样 频率 振幅 and phases repeating together in a 基础 周期 of definite 频率 the 基（础） is the lowest 频率 of this 复杂 and corresponds to the 独特 音高 听 in such a 复杂 音

The 基（础） does 不 一定 have the greatest 振幅 however and even if missing such as in the 案例 of a 低 voice speaking through the carbon 声筒（麦克风） of a telephone the 脑 will still identify that 频率 as the 基（础） called the periodicity 音高 or missing 基（础） This ability of the 听觉 系统 is called 基（础） 跟踪 源 Barry Truax - Handbook for Acoustic 生态学 CD-ROM Edition Cambridge Street 出版 1999 - CSR-CDR 9901