MySQL beta at CHEARSdotinfo co uk

单元 4

A 非线性 系统 改变 the 输入 波形 and 传递 a 失真（扭曲） 信号 at the 输出 The 失真（扭曲） 输出 包含 频率 components 不 in the 输入 信号 非线性 always 中项 失真 and 失真 always adds to the 输入 信号 something new and undesirable that wasn’t there before As with 放大器 and other 為耳/音频 设备 this is also true of the 人类 听觉 系统

Another 方法 for 检测 the 临场 of 听觉 谐（泛音） is by playing the 基（础） 频率 into the left 耳机 and injecting a probe 音 at the 频率 of a 谐/泛音 in the right 耳 and 聆 for a 双耳录音 拍（音）

These 听觉 谐（泛音） are 产生 by 非线性 of the 耳 and do 不 存在 as 外部 信号 Thus they are 不得 to any 物理 measuring 乐器 However their 临场 can be 验证 through these 双耳录音 拍（音） In fact knowing that strongest 拍（音） are 产生 when the two 信号 are close to the same 振幅 科学家 are able 不 only to 测 the 临场 of 听觉 谐（泛音） but also to estimate their 振幅

When two 音 are 介绍 into a 非线性 系统 a 系列 of so-called 组合 音 is 生成 If the 较高 音 has a 频率 H and the 较低 音 the 频率 L a difference 音 of 频率 H 减 L and a 总和 音 of the 频率 H 加 L are 产生 These are called the first order 总和 and difference 音

The situation becomes much more 复杂 as second order 失真 products are considered

For 例如 these include 频率 of 2H 减 2L 2H 减 L 2L 减 H 2L 加 H and so on In fact all these 失真 products are 类似 to what an 电子 engineer measures in an 扩器 by what is called the 交叉调制 方法

In addition to the simpler 听觉 谐（泛音） which we explored with a single 音 injected into our 听觉 系统 we have also 测 几个 组合 音 resulting from injecting two 音 into the 系统

With 樂/乐 many more than two 音 fall on the 耳 simultaneously Just 想像 the horde of 听觉 谐（泛音） and 组合 音 filling up the 可听 spectrum!

The 掩蔽 of 较高 频率 by 较低 ones makes some of these 失真 products 不可听 On the other hand we must remember that 失真 products 交互 with each other thus 创作 even more 失真 products But these will be at progressively 较低 级

In summary we can say that when modest 级 of 声波 fall on our 耳 all of these 失真 products 生成 in our heads are
at very 低 级 For 更响 声 however the 级 of 失真 do become appreciable In other 词 at 低 级 the 耳 is quite 线性 at 高 级 there is a departure from 线性