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* Phase

The starting point of a 周期 波形 on the y or 振幅 轴 is its 起始 相位 For 例如 a typical 正弦 波 starts at the 振幅 point 0 and completes its 周期 at 0 If we displace the starting point by 2π on the 水平 轴 or 90 度 then the 正弦 波 starts and ends at 1 on the 振幅 轴 By convention this is called a 余弦 波 In 效果（效应） a 余弦 is 相当于 to a 正弦 波 that is 相位 移位/偏移 by 90 度

In phase：two 信号 start at the same point

Out of phase：a 信号 that is slightly 延迟 with respect to another 信号 in which the two 信号

180 度 out of 相位 A is the exact opposite 相位 of another 信号 B

* Importance of 相位

A 滤器 相位 移位/偏移 a 信号 by delaying its 输入 for a short 时间 and then combines the 相位偏移 version with the 原始/原创 信号 to 创作 频率依赖 相位 cancellation 效果 that 改 the 频谱 of the 原始/原创

相位 is also 重要 in 系统 that resynthesize 声波 on the 基础 of an 分析 of an 现有 声波 In 特殊 these 系统 need to know the starting 相位 of each 频率 组成 in order to put together the different components in the right order

Finally much attention has been invested in recent years to 為耳/音频 components that 相位 移位/偏移 their 输入 信号 as little as 可能 because 频率依赖 相位 移位/偏移 失真（扭曲） 樂/乐 信号 audibly and interfere with 扬声器 成像 成像 is the ability of a set of 扬声器 to 创作 a 稳定 為耳/音频 picture where each 為耳/音频 源 is localized to a 特定 place within the picture 讨厌 相位 移位/偏移 is called 相位 失真 To make a 视觉 比喻 a 相位失真 信号 is out of focus