├── LICENSE ├── 倒相孔的故事.md ├── 家庭Hi-Fi声学指南.md ├── 家庭隔音指南.md ├── 小型录音工作室声学改善指南.md ├── 采样率之谜.md └── 频谱图怎么读.md /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. By contrast, 15 | the GNU General Public License is intended to guarantee your freedom to 16 | share and change all versions of a program--to make sure it remains free 17 | software for all its users. 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It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /倒相孔的故事.md: -------------------------------------------------------------------------------- 1 | 此篇为网友点播 2 | - 音箱为什么需要一个出气的孔？有的在前面有的在后面？然后买音箱回来就放在桌子上，不知道这个出气孔跟摆放位置是有关的，如果出气孔在后面，音箱就最好不要离墙太近？更加奇妙的是，还没有买音箱的时候，通过观察这个"出气孔"的位置，就可以大概判断音箱的声音取向？ 3 | - 这个气孔叫做 倒相孔， 作用就是把某些声音的相位颠倒一下(一般是低频)，或者说把声音的相位变为原来的180度，也就是相反的意思。 4 | ### 相位是什么 5 | - 简单解释相位：声波的本质是气压的快速变化，或者叫空气的震动。波峰对应高于大气压，波谷就对应低于大气压。当两个声波在空中相遇，波峰遇到了波谷就会互相抵消。波峰遇到了波峰就会叠加。理论上两个频率相同的声波，如果一个波峰刚好对上另一个波谷，就可以完全抵消，站在旁边什么声音都听不到。 6 | - 自然界中这样的情况很难发生，两个声波相遇，只会让一部分声音叠加，一部分抵消。但是在播放音乐的时候，喇叭振膜会向前发射声波，但也在同时向后发射声波，因为如果某一瞬间振膜前方是高于大气压的话（振膜向前顶出），必然会在振膜后方制造一个低压，反之在振膜前方制造了低压（振膜向后退缩），也必定会在振膜后方制造一个高压。在喇叭振膜前后形成的两个声波，振幅一样，相位相反（相差180度），如果让他们在空气中相遇，就会抵消所有的声音。这当然是无法接受的。 7 | - 好消息是这两个声波无法直接在空气中全部相遇，因为中间隔着振膜。但是坏消息是，有些低频和中频，可以通过衍射的方式通过振膜，这部分衍射过去的中低频就会遇到反相的自己，于是他们就抵消了。这就是声短路。最早的声音就是通过一个裸露的喇叭来出声的，如果有人试过只用喇叭没有箱体来播放声音的话，就会听到这种中低频被抵消的声音。 8 | ### 什么是低频的无指向性 9 | - 有经验的发烧友都知道我们人耳能轻易的辨别出高频声源的方向，而不能辨别低频的方向。如果单独播放一个低频，我们会无法听出这个声音从哪里传来。这就是低频的无指向性。所以我们一般可以把低音喇叭放在任意的位置，只要距离人和其他音箱一致即可。 10 | - 那么人是怎么辨别声音方向的呢？因为人的两只耳朵之间有一定距离，这种距离差异会影响声波到达每只耳朵的时间和强度。具体来说，当声波从某个方向传来时，它首先会到达最近的耳朵，然后再到达另外一只耳朵。这个时间差和声音的频率一起决定了声音在头部中的传播路径。较高频率的声音波长较短，更容易被头部阻挡或折射，从而产生更大的时间差。因此，当我们听到较高频率的声音时，可以更容易地感知到声源的方向。声波强度也会因为传播路径而产生差异。当声波在传播过程中遇到阻碍(人头)时，它会被散射和吸收，从而减弱声波的强度。因此，声波到达更远的耳朵时可能会比到达较近耳朵的声波更弱，这也可以帮助我们确定声源的方向。 11 | - 因为低频衍射的存在，低频被上面说的这种效应影响的程度要小很多。低频可以轻易绕过头部这样尺寸的障碍物直接传递到耳膜，所以对于低频就听不清方向。 12 | - 衍射是因为波可以说绕过比自己波长小一点的物体，对于低频来说，波长通常都很大，可以轻易绕过喇叭，人头这样的尺寸的物体。 13 | - 既然尺寸太小就会让低频绕过喇叭形成声短路，那加大尺寸不就行了吗。没错。不过加大振膜的尺寸并不容易，高速震动的振膜尺寸不能太大，否则强度不够。但是喇叭不光是振膜，只要连上一块板，都可以算喇叭。于是障板音箱就诞生了。原理就是弄一块巨大的板连在喇叭上，尺寸大了低频就过不去了。喇叭前后的短路就消除了，当然超低频波长巨大，还是不行，但是总是比原来强太多了。现在这个技术并没有过时，还有人用，只不过这东西体积巨大，有些是嵌墙安装，有些就独立放置，对空间要求很大。 14 | - 还是看看图： 15 | - ![图片](https://user-images.githubusercontent.com/42371034/226321488-70ce5daf-d4a9-4c9b-beb1-232893e7fd2f.png) 16 | - ![图片](https://user-images.githubusercontent.com/42371034/226321856-4443c2e1-cdb8-4dc9-942f-043807212b74.png) 17 | - 障板音箱效果好的关键就是板要大，越大越好。这就是一种古老的音响设计思路，出来的效果也不错，唯一的缺点就是占地方，让他无法被现在的市场接受。 18 | - 顺便说一下早期留声机那个样式也是障板的一种,对于低音来说就是隔绝低音,但是对于高音来说就是个号角,可以扩大高音的辐射角度.因为高音有很强的指向性, 和低音正好相反.指向性太强就会让稍微没有对准音箱的听众听不到高音, 这当然对于听音乐来说太严格了, 所以就会有号角这样的设计来扩散高音. 19 | ### 倒相孔的作用 20 | - 自从发现了声短路, 就有各种办法去解决, 除了障板以外, 还有个办法就是弄个箱子把喇叭包起来, 这样喇叭背面出来的声音就大大减少了, 声短路就大大减轻了.副作用就是喇叭背后变成一个密闭空间了,振膜在这个密闭空间振动的话阻力是比较大的.相当于喇叭的功率直接减小了,发热也增加了,一般这种密闭式的箱体在大尺寸音箱上使用效果更好, 因为喇叭后面的空间大,震动可压缩的空气也多,阻力也小. 这种密闭式箱体由于后面的声音小, 对音箱离墙距离没什么要求,声短路很弱,音质也好,一般都是比较好的选项.就是功率小,然后又适合大箱体,那么价格就不会很低. 21 | - 后来有更天才的工程师想出来一个办法, 既然喇叭前后声音相遇会抵消是因为他们相位相反,那我想办法给他的相位再反一次不就好了吗,这样音箱前后的声波相遇就不会抵消,不但不会抵消,还能叠加,这样就增加了低频的音量, 以后低频的功放还可以节省点功率,这样体积售价发热都能降低. 这就是倒相孔啦.倒相孔的名字就这个意思, 把声音的相位颠倒一下.这里要经过计算, 让低频出来的时候刚好经过了半个周期,这样才能和前面的声波相位一样,互相叠加增强.当然增加的只是音量, 下潜深度是没有变的. 22 | - 这个方案听上去很好,前面说了体积售价发热统统减小, 但世界上没有完美的事. 第一件事就是倒相孔对音箱后面的空间有要求, 如果后面有一堵墙, 那这个低音就会过于强(因为倒相孔出去的声音又会在墙上反射).相当于对于摆位有了更高的要求, 但是这个就阻碍了很多人的应用.于是后来又有了倒相孔在前面的设计. 当然前倒相也不完美, 因为倒相孔出来的声音又会在桌面上反射, 一样会污染声源. 23 | - 这个方案的第二个缺点就是, 所谓的180度倒相, 其实并不能做到. 因为每个频率的波长不一样,一根管子,不可能让每个频率都是刚刚好180度的相位翻转.那么就会有针对性地去选择一个大概的频率范围, 这个范围以外的声音就照顾不到. 24 | - 总的来说, 后倒相的音箱高频比较温和不刺激,前倒相的音箱低音好高音差一些. 封闭式箱体低音要想好听, 就要配功率很大的功放.但是封闭式总的来说失真较低,低频较紧. 音质最好的是障板音箱, 低音下潜好,声音通透松弛. 就是体积巨大. 当然这些都是同等条件下的对比, 现实中还有很多的变量. 良好的设计也能改善音箱固有的缺陷. 还有目前发展很快的数字调整补偿算法也会是未来的研发方向, 毕竟物理层面改进成本高又麻烦, 如果能用算法来补偿的话, 成本会很低. 当然目前dsp运算的效果还不能让我满意,也许以后会有更好的产品. 25 | -------------------------------------------------------------------------------- /家庭Hi-Fi声学指南.md: -------------------------------------------------------------------------------- 1 | ### 大部分人最关心的声学问题 2 | - 说到大部分人最关心的问题是什么呢？音箱的摆位？房间的装修？音箱的选择？在我看来在动手和买入器材之前要回答的是什么声音才是好声音。例如让人不由自主跟着摇头的低音很可能不是真正的hifi,只是播放器在低音上增强了而已。我心目中的hifi还停留在它原本的意思，高保真度，或者说低失真度。让听到的音乐更接近制作人听到的效果。 3 | - 怎么才是hifi的声音呢？如果没有听过标准的声音，就无法判断哪个才是好的声音，我的建议是跟耳机去对比，这当然有些困难，因为耳机效果和音箱还是有差距。但是从清晰度的角度去判断，大部分房间的清晰度都会远远不如耳机，这不是什么音箱的特点，而是房间声学的缺陷。用这个来判断低频尤其管用。 4 | - 如果用音箱听起来是轰隆隆连成一片的低音，但是耳机里面却很清晰的能听到低音的节奏，那么不用说也知道音箱的低音受到严重的反射影响。 5 | - 每个耳机又是不一样的怎么办呢。其实只要不买太过于娱乐化的耳机，他们差别没有那么大。Beats耳机，Sony的大部分耳机，还有Bose的耳机都是比较夸张，染色严重的。但是大部分监听耳机都还是有点节操的。例如Sony的v7506，7509， Beyerdynamic的DT770，990，Audio Technica的M50，Superlux的HD681 EVO之类，他们有细节差异，但是整体差异不大，用来检查房间的声学足够好。一般想要效果好，耳机都要用有线的，大振膜。 小耳机的效果是无法满足高音质的监听需求的。 6 | - 我以前讲过大部分5-6寸喇叭的音箱都不适合放在客厅用，链接：https://twitter.com/ddyykk2010/status/1539085699676524544?s=20 。就是由于放在客厅收听距离太远，超出了他们原本设计的用途。还有一个原因就是在没有声学处理的房间里，会有严重的声音反射（混响），如果耳朵离音箱近一些，听到音箱的声音会比反射声早，而离音箱两米远以后，反射的音量会在听到的内容里占更大的比例，效果会很差。而很多人把反射带来的浑浊的低频当成了澎湃的低音。正确的做法是把音箱放在桌子上，坐在桌子前收听。距离音箱半米左右。 7 | - 那么如果一定要在客厅里面hifi怎么办呢？（收听距离2米或者更长）那么首先房间一定要做声学处理，然后音箱最好都是8-10寸落地音箱或者配有大尺寸的低音扬声器。这样才能够有足够的功率。 8 | ### 家庭hifi的装修要领 9 | - 家庭影音室的装修其实和录音棚的听音室装修原则是一样的。 10 | - 对于听音的房间，装修要求叫做“前死后活”。就是房间的前面是死区（音箱背面，对于人来说就是前面），尽量把声音全部吸收掉，不管高中低频。从人坐的位置开始往后是活区，就不强调吸收，主要是扩散。（什么是吸收什么是扩散请参考另一篇讲录音室声学的文章：https://github.com/ddyykk/Audio_Stuff/blob/main/%E5%B0%8F%E5%9E%8B%E5%BD%95%E9%9F%B3%E5%B7%A5%E4%BD%9C%E5%AE%A4%E5%A3%B0%E5%AD%A6%E6%94%B9%E5%96%84%E6%8C%87%E5%8D%97.md ） 11 | - 这张图可以看到桌子后面的墙壁全部做了斜切的角度，里面就是两竖一横三块低频陷阱外加墙面的吸音。 12 | - ![IMG_20230203_223748R](https://user-images.githubusercontent.com/42371034/216638587-4d2a41a0-4163-417c-9e72-74ee2538c76f.jpg) 13 | 14 | - 然后从另一个角度看，椅子后面的墙面和天花板基本上就全部是扩散器了。 15 | - ![IMG_20230203_223819R](https://user-images.githubusercontent.com/42371034/216639454-137c0079-48b3-40c6-ac94-ce1b4f7f583b.jpg) 16 | 17 | - 为什么音箱后面要去做吸收？音箱后面的声音是从音箱喇叭发出的声音经过衍射，跑到音箱的后面。衍射的原理是障碍物尺寸小于波长的二分之一（具体多少不记得了），波就能绕过障碍。音箱发出的声音只有中低频可以绕过音箱传播到音箱背面去。还有些音箱后面有倒相孔，也会有低音出来。所以死区的低频陷阱就是比较重要的。不然这些低音就会在墙角被反射，形成浑浊的低音。 18 | - 这里又有人可能要问了，在录音室的声学处理中我说可以只做扩散，放弃低频陷阱，这里可以吗？答案是不可以。录音不做低频吸收是因为有很多人只录语音，但放音乐和电影可是有低音的。 19 | - 听音室里面的活区就比较简单了，声学扩散器铺满，或者自己用生活用品拼凑。扩散的作用就是让高频不会集中反射，带有一点混响，可以让音箱听起来明亮自然。如果没有扩散，那么听起来就是类似耳机的效果，听起来不像是在一个房间里。 20 | - 很多人可能第一次听说前死后活这个专业说法，为了证明不是我瞎编的，我找几张图片给大家看看。 21 | - 这个就是外国的专业录音棚，可以看到音箱后面的墙角也被用来做低频陷阱了。墙面上除了一个观察窗，其他地方也是吸音材料。 22 | - ![tinified-2021studio-01](https://user-images.githubusercontent.com/42371034/216640067-4ddf1e34-d7ef-4df0-a7a2-d09c1a505d39.jpg) 23 | - 然后这是背后的角度，后面也放置了一个巨大的扩散体，他的侧面做了吸收，顶面这个图片看不见，但是总的来说还是符合前死后活的。如果希望声音更干净，确实可以在身后放置一定面积的吸收材料。 24 | - ![tinified-2021studio-02-e1640158377549](https://user-images.githubusercontent.com/42371034/216640348-78b9f01f-a1aa-42bb-b606-ee21ffe3c53d.jpg) 25 | - 对于家里不想花钱做专业装修的人，最低限度应该做以下三点：音箱尽量不要贴着墙放，最好留 20cm 或者更多空间。 贴着墙会让低音大大增强，音箱的高中低频就会失去平衡。在房间里放一些类似低频陷阱和扩散器的东西。扩散应该比较简单，就是找个高一点的架子堆砌杂物即可。低频陷阱比较难，可以尝试床垫，沙发床之类的，一定要放在墙角。其实会点木工的话自制低频陷阱并不困难。YouTube上bass trap的制作教学影片很多。 26 | - 如果要自己在房间内布置低频陷阱，不要一开始就把买来的玻璃纤维全部填满，填的太多可能会让音箱低音太少，要听一听，跟耳机比较一下，边听边放。 27 | ### 音箱的摆位 28 | - 摆位有两件需要关注的事，音箱在房间里的绝对位置和人的相对位置。 29 | - 前面说了，倒相孔在后面的音箱，不宜离墙太近，会造成低频加强。当然所有的音箱离墙太近都会加强，但是倒相孔在后面的音箱这方面问题尤其严重。这也是为什么有些音箱要把倒相孔设计在前面，就是为了让有些用户不用受这么大限制，毕竟很多人家里只能紧贴着墙，也算聊胜于无。那么大概多远呢，一般以20cm为起点，远的话没有限制。很多音箱后面有EQ，可以减弱低音或高音，但是能摆位解决的，尽量不要调EQ，EQ往往会带来相位失真。 30 | - 那么音箱应该离人多远？这个简单，人和两只音箱应该成一个等边三角形，注意是等边三角形，不是等腰三角形。等边三角形每个内角都是60度，三条边都一样长。这样才会获得最合理的声场宽度和深度。这个看起来容易，其实很多人并没有做到。最常见的家庭hifi是音箱放在电脑桌上，很多人喜欢双屏幕，往往音箱的距离就奔着一米去了，但是人却离桌子很近，听起来声音超级宽但是中间空虚。还有一个常见的家庭hifi场景是音箱放在电视两边，人坐在沙发上。家里客厅一般是狭长形，能做到等边三角形的少之又少。如果按照这个标准，很多人的桌面配置就要重新考虑了，大部分人电脑的使用距离也就是身前半米左右，再远眼睛要看不清屏幕了，如果要买大屏幕，超宽屏幕，多个屏幕之类的，会影响hifi效果哦。 31 | - 解决办法是将音箱吊装，角度向下倾斜，对准用户。有一些成本。还有一种土豪，很需要大屏幕，于是将音箱之间摆的很宽，然后放远在音箱架上，这个需要房间比较大，桌子后面还有空间。如果这两种都没有条件，就只好缩小屏幕尺寸。或者hifi和工作用电脑分开两套系统。 32 | - 等边三角形示意图： 33 | - 34 | ![图片](https://user-images.githubusercontent.com/42371034/217468230-cdb8effc-5e2a-41c9-8730-4d43bd929799.png) 35 | 36 | - 还有些人使用的是2.1声道系统，多了一个低音扬声器。这个扬声器的摆位也需要注意，有些人就摆在脚下，有些人摆在其中一个音箱旁边。要知道声音的传播也是需要时间的，最好听者到音箱的距离都是一样的，如果低音喇叭太近或者太远，就会造成低音太快或者太慢，听起来肯定不舒服的（相当于一个相位失真）。 37 | - 摆放低音扬声器的要点是，低音扬声器的具体位置不重要，因为低音指向性不明显（但最好还是不要放在身后），也就是听不出来声音从哪里传过来。但是低音扬声器到听者的距离一定要和左右音箱到听者的距离一样，用皮尺测量一次，这很容易的。尽量测人耳到振膜的距离。 38 | - 最后提醒一点，这里说的摆放技巧之类的，起码应该是6-8寸的书架音箱，或者说有一定hifi属性的音箱才能听到效果。几百元的娱乐音箱，蓝牙无线音箱可能听不出太大效果。比如苹果的HomePod这类蓝牙音箱，设计的时候就是向四面八方发射声音，就算两个组合起来，不管怎么摆位，声音也是有点奇怪的。这个详细的留到5.1那一节再说。 39 | 40 | ### 最适合家庭的音箱尺寸是6-8寸 41 | - 为什么是6-8寸的喇叭最适合？因为太小的话没办法发出比较低的低音。太大的话会发出太低的低音，往往在家很难处理得当。大音箱和小音箱，或者说便宜音箱和贵音箱的最大区别不是高音，高音相对容易，而是低音音质。而低音又是整个音乐的根基和骨架，是音乐中最重要的部分。音乐的节奏，能量，律动，和声的感觉基本上都是低音决定的。贵的音箱就是低音的音质较好。 42 | - 那么具体来说6寸-8寸的喇叭能发出多低的声音呢？这个要看具体的设计和材料还有售价。但是我可以给你大概的范围.6寸的音箱一般能达到120-150Hz的下潜深度。8寸可以达到80-120Hz的下潜深度。 43 | - 这时恐怕又会有人问了，人耳能听到的频率范围不是20-20000Hz吗。原来音箱都达不到吗。是的，只有很贵的大音箱才能发出20Hz的声音。可能是12寸以上的喇叭，或者低音喇叭。 44 | - 这时候又会有人问了，那音乐或者电影里面的声音最低有多少呢？以我的经验来看，其实很多音乐里面的大鼓（kick drum）和低音吉他（bass）都能发出30-40Hz的声音。电影也是类似。所以我们的信号确实是有很多低音在里面但是我们听不到的。因为我们的扬声器不够贵。但是听不见这些频率并不会对欣赏声音造成很大的困扰，听不到30Hz的声音不等于听不到大鼓和bass，这些乐器能发出这个频率但不是只能发出这个频率，所以还是能听到他们存在的。在钱财有限的时候就可以取舍啦。 45 | - 这时候又会有人问了，我买的音箱、耳机包装上写的清清楚楚，频率响应范围（Frequency Respond Range）是20-20000Hz，有些还不止，比上面的范围还要大，高频可以响应25000，30000，40000Hz的都有。对于他这个设备高音能不能响应超过20000Hz我不知道，因为我真的不知道。人的听力范围是20-20000Hz，这个科学实验在我看来还是很严谨和完整的。而且这是一个相当宽松的范围，因为大部分人的耳朵听到的频率范围都达不到20-20000Hz这么大。医学上诊断人有没有听力缺陷，测试用的最高频率都是10000Hz 或者 16000Hz。能听到这样子已经在医学上属于正常了。所以才把超过20000Hz的频率称为超声波。 46 | - 我个人是不能听见超声波的，别人在哪里听见的，我不知道。有些喇叭和耳机宣称能回放超声波，我也没有办法验证。但是很多小喇叭和耳机上写的频率响应20-20000Hz，这个20Hz就属于混淆概念了。既然叫做频率响应，就是说，有一个20Hz的信号过来，只要有响应就行。但是有可能500Hz的信号喇叭会发出100%的音量，100Hz的信号就只有10%的音量。但也不能说人家没有响应啊是不是。至于一个音量那么低的低音放在音乐里听起来是什么样，那可能就是听不到啦哈哈，都不用10%，可能70%都会听不到了。每个频率发出的音量画出来的曲线就叫频率响应曲线，也叫频谱图。（spectrum diagram）。 47 | - 偷偷告诉你，5寸的喇叭可能才能发出180-200Hz的声音，小小的耳机也很惨，大概最低能发出100Hz-200Hz的声音而已。原来听到低音这么难啊，对，大部分人可能从来没听过音乐里的低音部分呢。 48 | - 总结，我个人推荐的家用hifi喇叭尺寸是6-8寸（5寸也勉强吧），他们能发出80-160Hz的低音，不需要过于夸张的装修，不需要过大的房间，这个尺寸也是主流产品会去覆盖的。 49 | ### 最适合家庭的hifi是有源音箱 50 | - 本节为历史故事。 51 | - Hifi这个词的来源其实是90年代初，那时候的音箱失真普遍比较大。如果想要做失真小的音箱，就要用甲（也叫A类）类放大器，功率极其有限发热还巨大。好的线性直流电源也是体积大，发热大，功率小。如今常见的开关电源和低失真D类功放都不存在。民用的音频产品失真很大的背景下，高端器材厂商提出了hifi，高保真的概念。 52 | - 在当时电脑并不普及，手机也不普及，家庭娱乐很缺乏，hifi就相当于今天的PS5或者iPad之类的东西，属于有点钱的白领阶层才能享受的爱好。价格来看也是很高的。价格高带来了高利润，刺激了一大批厂商投入这个行业，现在大部分都已经消失。没有消失的也转型做别的了。 53 | - 当时hifi的主流搞法是，一个信号源，可以是cd机，磁带机，LD，MD机，甚至唱片机。然后会有个信号处理器，一般是个图形EQ。有些家里爱好卡拉OK的还会有混响器和磁带录像播放机，当然信号处理器也会整合混响功能。然后处理好的信号送入功放，功放连接音箱。这种音箱本身是没有电的，音箱的线既是信号线也是电源线可以驱动喇叭发声。所有的信号处理都在音箱外面完成。这就是无源音箱。 54 | - 但是后来hifi这个词渐渐变成了贬义，因为很多hifi爱好者追寻的已经不是音质，而是美好的声音，哪怕信号原本没那么好听，也要在器材上补偿。偏离了高保真原来的含义。 55 | - 说句题外话，电子管功放据说很好听，那么他到底是不是高保真呢？其实不是，电子管会带来一个偶次谐波失真，还会非线性的压缩信号，是很好听没错，但好听的失真还是失真。 56 | - hifi行业家道中落已经很久了，现在除了少部分恋旧的人，很少有人热爱追求极致的音质了。没有消费者，厂商自然不会投入精力去研发高性能的产品。如今的音频产品基本上都在信号处理，无线连接，外观和便携之类的地方想办法，音质也朝着数字化调节、算法加料的方向去走。无源音箱和功放几乎没有什么大厂商去涉足，仅剩一些小厂只能以纯手工的方式维持，产量太小，没有办法开流水线。而且功放和无源音箱之间的搭配也是一个无止尽的话题，每一个功放和喇叭的声音都不一样，要想找到好声音难度很高。 57 | - 目前的hifi界基本上都转向有源音箱了。有源音箱就是我们常见的样子，插上电源和信号线就可以用，功放在音箱的内部。这样功放在设计的时候就可以考虑匹配喇叭的问题，音质损耗小一些。而目前的有源音箱，很多其实都是为了录音室的监听设计的，就算是美化声音的音箱，很多也是由监听音箱修改而来的。主流的音箱牌子例如Focal，Adam，EVE，Genelec，Dynaudio，Yamaha，Monkey Banana，KRK，KEF，Neumann本身都生产过监听音箱，但是监听音箱毕竟销量小利润低。所以也会推出针对发烧友的型号，还有些发烧友喜欢追求录音棚的音箱效果，也会直接购买监听音箱来听音乐。 58 | - 总结，我个人不推荐购买无源音箱，成本高，音质难以琢磨。有源音箱使用方便体积小，主流的品牌都推出有源音箱了。 59 | ### 5.1声道有必要么 60 | - 5.1声道需要关注两个问题 61 | #### 我们期望5.1能放出什么声音？ 62 | - 对于音乐类，一般听众脑海里想象出来的画面应该是乐队在面前表演，也就是说所有声音都来自面前。这样的想象也符合现实中的场景。而使用5.1声道来回放音乐，感觉就是自己站在中间，四周围了一圈乐手在给你演奏，也不是说不行，一般人可能不太习惯这样的一个声场，我就不太习惯。 63 | - 对于电影类的内容，基本上也是类似的画面出现在想象中，视频的内容都发生在眼前，声音也来源于眼前才比较符合想象，画面在展示眼前的事物，这时突然描写一个来自身后的声音，在电影里面虽然不是没有，但也是很少见的。为了这样的内容而去设立一整套代价高昂的系统是否值得，我个人认为身后的两个音箱是得不偿失的。 64 | - 最后一个5.1声道确实有用的场景就是游戏了，主要是3D游戏，会有听到身后声音的需求。那么我们接下去看这个系统的成本。（大部分人都是不会用5.1系统玩游戏的吧） 65 | #### 我们要付出什么代价来得到5.1 66 | ##### 房间的代价 67 | - 这里假设我们已经有了一个房间，那么如何摆放5.1的系统呢，在杜比的官网他们会推荐这样摆放： 68 | - 69 | - ![火狐截图_2023-02-08T08-17-19 997Z](https://user-images.githubusercontent.com/42371034/218703624-7845c525-b0d8-4689-aa2c-3bdf327c9f68.png) 70 | - 这个摆放也是大多数商家推荐的方式，也是对于大多数家庭可行的方式。很可惜，这是一个极大妥协了效果的方式。他在声学上有很多硬伤。首先是音箱靠墙太近，会造成我前面文章说的低频增强，对于一般没有声学处理的家庭来说低音清晰度很差。然后是每个音箱到观众的距离差异很大，声音有的快有的慢，这样会造成声场混乱。最后一个硬伤就是后置音箱根本没有后置，放在了侧面，失去了意义。但是这些问题又是没有办法的，为了让更多人接受5.1系统，只能妥协成这样，我相信大部分家庭的音箱都只能靠墙放置的。我倒是见过有自己影音室的土豪，后置音箱确实是放在后面的，前面的三个音箱也是没有靠墙的，但那样的条件对于绝大多数人我相信是不太现实的。而这个土豪有那么多钱依然没能正确的做好声学处理，被人忽悠在家里贴了不少海绵却没有低频陷阱。那么全部都能做到的除了电影后期的混音棚，其他的地方存在的可能性很小了。 71 | - 在这样一个妥协的5.1系统中，我们能听到精准的空间定位几乎不可能了，后置音箱离人最近，声音最先被听到，然后是前面的音箱，这样怎么能听出是后面的呢。再加上靠墙摆放以后比较混乱的低音，也会破坏定位的清晰度。造成的结果就是声音都是模模糊糊的一团。 72 | - 如果有人去购买5.1系统，商家推荐的，甚至请人来上门安装，都会是上面图片的结果。 73 | - 那么正确的音箱摆位是怎么样的，请看： 74 | - 75 | - ![火狐截图_2023-02-08T08-18-29 565Z](https://user-images.githubusercontent.com/42371034/218708522-55a4a343-7757-4bee-8845-7fa0fd2b29c4.png) 76 | - 我想对比这两个图片就知道为什么5.1需要妥协了，因为这样放实在太占空间了，客厅这样放走路都不方便。书房这样放，不仅走路不方便，而且别的啥也做不了了。因为每个音箱还要有支架和线材，有线材就可能要电源（插座、插板），房间里拉这么多线已经快成一团乱麻了。 77 | - 可能这样说还是不够直观，我们把两张图片叠加起来看就知道为什么大部分人的家里没办法这样摆了： 78 | - 首先是后置音箱的距离优先摆放： 79 | - 80 | - ![1](https://user-images.githubusercontent.com/42371034/221075297-fc8c52fa-08c9-4a64-ad02-a138304b5757.jpg) 81 | - 看到了吧，音箱把客厅弄得没法走了。然后再看如果优先考虑沙发和电视的距离： 82 | - 83 | - ![2](https://user-images.githubusercontent.com/42371034/221075522-5de9e18f-2f71-4a3d-8dae-73b9d31e2e31.jpg) 84 | - 这样就会发现后置音箱需要巨大的空间，也就是沙发要摆在房间的正中间，我相信就算有人的客厅是正方形，应该也不舍得这样摆。 85 | - 如果能完全做到这个布置确实可以得到精准的声音在空间上的定位，但还有一个前提，那就是有5.1的音源。很多的电影的5.1恐怕也不是真正的5.1制作，而是杜比的虚拟5.1技术自动生成的。更不用说有时还被盗版压片的省略了。所以5.1的文件获取成本也不低。 86 | - 其实就连电影院自己的5.1都做不到精确定位，因为电影院的音箱都挂在两边的墙上，并不是一个圆形围绕在身边的。去过电影院的人不在少数，有人听出了声场内精确的空间定位吗，没有吧。什么是精确空间定位？可以搜索一下人头录音，听一听用人头话筒录制的声音，就知道什么是精确定位，记得用耳机听啊。 87 | - 例如：https://www.bilibili.com/video/BV1zs411y7Eo/ 88 | - 以及：[https://www.bilibili.com/video/BV18541187Yc/ 89 | 90 | - 在电影院里从来不能给我这样精确的空间声音定位，而人头话筒是几声道呢，2声道而已。 91 | ##### 设备的代价 92 | - 设备上需要注意的问题是什么呢？大家买5.1的系统，肯定是成套购买的对吧，一次6个音箱，说明书会告诉你哪个是主音箱，那个是前置，哪个是后置，就算不告诉，很多时候从他们的尺寸也能看出来。如果这样搭配也是有很大问题的呢？先给大家看看专业的5.1配置图片： 93 | - 94 | - ![图片](https://user-images.githubusercontent.com/42371034/218715039-299adfe3-1fab-4742-ac87-92ae11446d8f.png) 95 | - 重点在哪里？他们的音箱全部是一样的！图上只有3个，但其实除了低音炮，剩下5个都是一模一样的。这也是为什么监听音箱大部分都是一只一只卖的。只有这样才能保证5个声道的音质是一致的。 96 | - 假设后置音箱和前置音箱尺寸音质都不一样，那听到的前面和后面的音质差很远，搭配起来肯定不会好听的吧。应该没有人喜欢声音一部分音质好，一部分音质不好的吧。大部分民用厂商所谓的一套5.1系统在音箱的配置上又一次的“妥协”（阉割）了。为了降低成本。 97 | - 总结，我当然不会反对有兴趣的人享受5.1的乐趣，只不过这个系统的成本不是一般的高。要准备大房子用于牺牲，要声学装修，还要购置昂贵的音箱系统，用很浪费空间的方式摆放，然后要有5.1 的文件，才能享受。 98 | ### 加更一节环绕声 99 | - 以前环绕声就是指5.1，7.1这一类技术的，但是现在sony，bose这类牌子说的多扬声器环绕声意思已经发生了改变。原因是受到apple的HomePod一类的产品影响，也开始推出覆盖整个房子的音响解决方案。用几个音箱之间互相连接，可以在房间任意位置都能听到音乐。 100 | - 常见的听音乐的系统是两声道的，俗称立体声。但是HomePod只有一个，那当然就是单声道了。就是将立体声的信号加在一起变成单声道。这样一来音乐里面的声场之类的东西都消失了，只有一个点声源发出所有的声音，没有了左右区别。在混音制作中，对单声道的兼容性也是考虑因素之一，毕竟不是所有人都听立体声的，手机，收音机，ipad都很有可能是单声道的。就算有两个音箱，如果人离得太远，两个音箱之间的距离可以忽略不计，那也是单声道，比如很多号称立体声但是喇叭都挤在一起的蓝牙音箱。 101 | - 如果在每个房间都放上HomePod这类音箱，并且让他们同时响，那就得到了一个很均匀的，在哪里听起来都差不多，对音箱摆位不太敏感的，单声道的播放效果。其他牌子的所谓环绕声也是这个意思。注意要跟以前的环绕声区分，新时代的环绕声不再注重声场的听声辨位，只是在房间里处处有音乐而已。 102 | ### 耳机hifi要注意健康问题 103 | - 耳机其实是一个音量很大的播放设备，因为它极端靠近耳膜。如果在嘈杂的地方比如家里客厅使用耳机，一般起始音量就不小了，要不然不能盖过噪音。还有耳机会压迫耳朵上的神经和血管，很容易引起疼痛。所以我个人的建议是，入耳式的小耳机，大概半个小时就要休息了。耳罩式的大耳机也不应该超过两小时。 104 | - 由于离耳膜近，耳机的高频自然衰减很少，和音箱很不一样，听起来声音会炸很多，这个事情也是容易损伤听力的，所以我更偏爱动圈耳机，不喜欢动铁之类金属振动发声的耳机。这些耳机虽然解析力清晰度很好，但是是用很多高频换来的，而耳朵对高频的敏感性是随着使用耳朵逐渐下降且不可逆的，能保护还是尽量保护。 105 | -------------------------------------------------------------------------------- /家庭隔音指南.md: -------------------------------------------------------------------------------- 1 | - 录音棚的声学装修一般有两个部分，室内的声音优化，和录音间内外的物理噪音隔离。还是从基础物理开始，要隔音就要研究噪音是怎么传播的。最常见的传声介质有空气和建筑物本身。那么隔绝噪音也就是在这两个介质上想办法。 2 | - 这里我讲一些稍微枯燥的理论：不同的介质适合传播不同的声音频率。越是坚硬的物体就越是难以传播高频，即他们会倾向于传播低频。例如水泥墙和玻璃，大部分频率的声音都会被反射回来。柔软一些的木头就能传播一些中频。而最柔软的空气会传播所有的频率。（人耳可听见的频率在20-20kHz） 3 | - 这就是为什么我们如果隔着墙壁听音乐，总是能听清鼓和bass的声音，听歌词的话就比较模糊。而且声音在介质中传播的距离取决于声波本身的能量大小，也就是振幅，或者说音量。音量越大，传播距离就越远。介质越重传播就越难。那是不是说听室外音乐会在前排和后排听到的一样呢，因为是空气介质，并不是。 4 | - 因为能量和音量不是完全相等的。室外音乐会在远处听起来就像是隔了墙壁一样，低音很清楚，人和高音乐器就不太清楚。原因是高频震动的能量要远远小于低频震动。低音乐器、低音喇叭的尺寸都要大得多，因为发出低音会耗费巨大的能量，他们也能传播的更远。 5 | - 然后来看实际问题。如果要在家录音，家里的人要看电视、说话、做饭等发出声音怎么办。这些声音其实音量不会太大，主要是一些中频，传输介质也是空气。一般的解决办法就是关门然后在门窗贴上尽量密封胶条塞住门缝，只要不让空气交换，那么就可以隔绝声音。有些门是空心的，就换用实木或者玻璃门 6 | - 如果住在街边，车水马龙，这时候其实除了中频，一定会有低频（是的马路上有低频），除了隔绝空气，沉重硬质的门窗，水泥造的房屋都比木质的房屋隔音有优势。但是低频的影响不会太大的，除非要录乐器，否则要录的频率和噪声频率并不会重叠，可以在电脑上用EQ轻易处理掉。（应该知道怎么用EQ吧,如果实在不知道以后再说） 7 | - 还有一种解决方法，就是尽量晚上录音。很多地方这样做不是因为白天要睡懒觉，而是晚上整个城市的噪音都会比白天小得多，用毛巾毯子之类的把门窗塞紧，在里面大声唱歌也没问题。还有些人会把自己包在一个被子搭出来的空间里，网友戏称被子棚，也可以起到一定的隔音作用，但是注意，这样录的声音很闷糊，具体上一篇已经说了。包在被子里和包在海绵里是非常类似的。 8 | - 以上可能只适用于水泥材质的房子，木质的房子隔音有先天的劣势，木头材质比水泥轻太多，对声音的阻断很差，尤其是中频和低频。解决办法就是把房子拆掉重新盖成水泥的。不行吗？那就在木头房间里用水泥砌墙，保证隔音性能大增。 9 | - 好吧不开玩笑，木头房子确实没有特别方便的办法。如果想省钱那就想办法加厚墙壁和地板。比如刷墙，再贴墙纸，挂被子毛毯，如果是两层楼就给地板也这样弄。换能密封的实心门和窗户。房子周围多种树。再躲在被子棚里。这样隔音会好一点，不能完全安静，但在不用施工的前提下这就是极限了。 10 | - 别忘了市场上卖的那些海绵声学毯之类的，你把他们挂在房间所有的墙面上也是可以的。网上还有数不清的文章和视频教你怎么做，把房子的每一个可能漏气的缝隙都给密封好，没法密封的想办法加一层隔音棉之类的。例如：https://www.everest.co.uk/windows/noise-reduction-window/how-to-soundproof-room/ 11 | - 如果有人愿意投钱下去改善房屋声学的话，那我也简单说说专业的做法，只能简单说说，毕竟我不是做声学装修的，这些都是在录音棚接触多了听回来看回来的。要做还是找专业的设计师。 12 | - 隔音效果最好的：钢筋水泥，然后是各种声学设计。我知道一种常见的是墙的表面留10cm厚的空腔（用龙骨架起来），用薄木板封住，外面填充20-30cm厚的玻璃纤维，四面墙都要做，然后用布封上（也有用带有很多孔洞的木头的，只要声音能穿透即可）。这个结构让声音在玻璃纤维层会被吸收大半，然后进入密封空腔又不能出来，外面的噪音进来也是一样被吸收，虽然顺序反过来了。 13 | - 房子的顶上如果想省钱就用毛毡配合玻璃纤维填充满，要效果好就按照墙面做空腔和玻璃纤维层。底面可以铺设厚重的橡胶层（成本极高），或者架空填沙子。然后房屋内部漏气的缝隙全部找到并且密封住。门的话隔音门一般都极其厚重，图上是我家的隔音门（可以看到厚度超过我手掌，600KG），录音棚一般会做两道相距 1-2 米的隔音门构成声闸，会隔绝的更彻底。 14 | - 15 | ![216117234-4877c6eb-c850-4b86-9613-9eaf89c60830](https://user-images.githubusercontent.com/42371034/216117930-9184f4ba-62c5-4a6d-b3ec-9f766b81502f.jpg) 16 | - 最后需要提一下的就是隔音用玻璃纤维的寿命。如果经常需要振动吸收能量，玻璃纤维的寿命在3-5年。所以并不是装修一次就一劳永逸，在铺设的时候考虑以后更换方便，提前预留维修余量，不要把整个结构全部拆掉才能更换。震动失效的玻璃纤维会变成粉末状，在施工更换时会污染空气也要小心。 17 | - 总结，房屋隔音基本思路就是能增重的增重（固体传声），能密封的密封（空气传声），要么就是毯子被子到处裹，包的严实就能隔音。还有马路上的噪音晚上九点以后会小很多。 18 | - 有人可能会问不是上次才说海绵被子毛毯没有用吗？上次说的是他们放在室内对录音的音质没有好处，但是可以隔音。如果需要隔音，可以把毛毯被子用来隔音，房间里面照样要做扩散处理。这样就更像一个专业录音棚，隔音和声音的美化处理都具备。但是网上有很多的视频可以看到用这样的房间录音，那个房间并没有处在噪音的环境之中，之所以在墙上贴满海绵，只不过以为这样声音会更好，因为看到网上大部分人也是这么做的，到底为什么要贴其实不清楚。 19 | - 如果以上所有的都嫌麻烦，没动手能力也没有钱没时间，但是我就是想要我的录音没有噪音怎么办？什么？你说后期软件降噪？那怎么行啊，软件降噪完声音不能要了。只有电影行业某些情况下实在没办法才会后期降噪的，一般音乐行业都是杜绝后期降噪的。还有最后一招：没钱就用力气来弥补。 20 | - 把话筒的录音音量尽量开小，说话唱歌尽量大声吼。如果用的是电容话筒开最小了音量还是过大就用动圈话筒。这样声源的音量是远远超过噪音的音量的，听起来声音就会很干净，像是没有噪音一样。我曾经用这个方法在闹市区的马路边录音，录出来和录音棚一样安静的声音，当然我录的乐器本身容易做到音量大。但是一般人家里的噪音也不会像闹市那么大的，所以也没有那么困难。这时就会有人担心自己大声吼录出来的声音不自然，好像用力过度一样。其实不会，专业的播音员和歌唱家音量都非常大的，他们专业训练有一部分就是要让音量很洪亮然后吐字又要清晰好听，这样才容易让人听得清楚不是吗。 21 | - 有些网友可能会担心动圈话筒音质不如电容话筒的好，这也是另一个很流行的错误说法，可以成为我以后的一篇文章。简单来说就是那么多大牌明星演唱会都在用的东西怎么可能音质不好呢？不用担心。 22 | -------------------------------------------------------------------------------- /小型录音工作室声学改善指南.md: -------------------------------------------------------------------------------- 1 | 网上这方面信息很少，需求也很少，作为一个当过录音师的人，想把自己的知识传播开，记录一下： 2 | - 最常见的上当的一点就是录音室一般都是小房间，很多人都会购买海绵贴满墙壁，或者买大海绵罩子围在住话筒周围的一圈。但这样做只会让声音闷糊失去清晰度。网上这样做的人还不少。类似的产品也不少。这些东西通通和专业不沾边，更多是一个心理安慰。 3 | - 海绵或者类似的棉被毯子之类的物体只能吸收高频，对于造成声音在房间里面浑浊的中频和低频毫无作用。而在房间里面反射的高频能够增加声音的亮度和自然的感觉，在声学设计中是需要保留和扩散的。如果不需要录乐器，只要录语音，那么主要的工作就是声音的扩散，然后配合适量的低频陷阱来吸收中低频即可。 4 | - 低频吸收的原理是吸音材料将空气的震动转化为热能，从而吸收了震动的能量。但是需要进行低频共振的话，物体的尺寸需要和声波的波长的1/2相同才行，低频的波长往往要2-4米，那么要吸收低频也就要长度1-2米的物体。而低频往往是在房间的角落反射的，所以低频陷阱一般都是占据房间角落的样子。（网图） 5 | - 6 | ![Fns4V1CaQAE1upm](https://user-images.githubusercontent.com/42371034/215976394-8fbda5d3-3835-403f-b263-3a776ae888f3.png) 7 | - 高频扩散的意思是，声音其实会像光一样在物体表面反射，如果墙面平整声音就会集中反射，和声源叠加在一起的话会给声源一个不好听的染色。我们希望得到的是一个类似漫反射的效果，让高频在房间里面四处反射，这样更接近我们在生活中的效果，所以听起来自然。全部吸收掉又会听起来干巴巴的。 8 | 9 | - 扩散体实例： 10 | - 11 | ![Fns5l5uaUAAe2K9](https://user-images.githubusercontent.com/42371034/215976601-b80bf208-e596-4488-a60a-726f71b71085.png) 12 | - 如果不想费事，可以在淘宝购买成品安装到房间里，扩散器面积越大效果越好，低频陷阱越长效果越好。天花板上可能需要请工人安装。还有个反射面是大部分人的录音要用桌子和屏幕，如果不用就会少两个最直接的反射面，（专业的都不用）如果一定要用尽量调节角度让他们不要直对话筒，或者用心形指向的话筒。心形指向的话筒对来自后面的声音有个很大的衰减。 13 | - 以上就是最简略版的声学改善方法，简单，有效果，但是有点花钱。然后如果不想花太多钱的人可以考虑自己加工低频陷阱和扩散器。主要是木工活，填充材料需要无纺布和玻璃纤维，玻璃纤维纯度越高的越好（越白越好，也会越重），网上也有教程。在YouTube搜索basstrap，就是低频陷阱。扩散器的英文是acoustic diffuser。 14 | - 简单处理后的效果可以参考这里的视频，比较部分从11分开始，（比较了空房间、海绵、吸音板）最好用耳机听。(https://www.youtube.com/watch?v=VHCbO6psdIw) 15 | - 对于大部分主播一类的人，不需要录乐器，只需要语音清晰，还有一个可能不花钱的办法就可以极大改善录音室的声学。语音的低频成分并不多，主要还是中频，这时我们放弃低频陷阱，只做扩散也会有很不错的效果。成品扩散器很贵那么就自己用生活用品堆砌一个类似的东西出来。虽然效果不是完美，但是已经比空房间或者海绵好太多了。 16 | - 自制扩散器的思路是让物体表面不规则，不要有完整的平面。同时最好有一定的深度（20-30cm），这会让一些声音进去不容易出来，相当于吸收了。同时面积要够大，最好房间六个面有五个都是这样的。地板要走路没办法。具体用什么，就看身边有什么，常见的书架，纸箱子，各种杂物都可以。一定要把房间堆满。 17 | - 堆满以后录音清晰度会有巨大的提升，房间里面的东西是可以调整的，效果不好可能是堆得不够满或者太满了，需要自行调整。地板可以用地毯弥补，越厚越好。具体的例子参考这个视频的3分50秒 和 9分钟位置。此人曾是好莱坞的从业人员，专业水准极高。https://www.youtube.com/watch?v=zLF6Bru6vI4 18 | - 另外有个有趣的知识是常常有影视作品渲染浴室的声音效果好，唱歌听起来很好。这是因为浴室四面都是光滑的墙壁会产生巨大的混响，自我陶醉的时候清晰度低反而感觉好听，但录音是这个效果的话，没有几个人接受的，不信去录一下试试。 19 | - 小工作室还有个常见的问题是电脑和空调的噪音。专业录音间不会把电脑和空调放在里面，空调都是用风管送过来，一般人不可能这样奢侈。简易的办法是在墙上钻孔把主机放出去，但是很多线材长度也是有限的。还有个办法就是用录音笔（高品质的录音笔音质比很多便宜的声卡加话筒还要好），或者房间里只放一个话筒，主机放外面，话筒线一般是可以比较长的。这样的缺点是一个人录音要来回跑。 20 | - 现在也有很多电脑能做到很低的噪音，那么就要对硬件比较了解才行。比如不要用高性能的cpu，不要显卡，要用大规模的散热器和猫头鹰的静音风扇。电源要用1000W左右的，这样在使用的时候电源的风扇就不会转，仅靠被动散热就可以应付工作。空调是最不好解决的，我知道的方法只能是先把房间温度降低，然后关空调赶紧录音20分钟，休息一会再重复 21 | - 这就是简易的录音室声学改善指南啦， 如果有问题可以讨论。下次有空我可以讲讲简易家庭HIFI声学指南。 22 | -------------------------------------------------------------------------------- /采样率之谜.md: -------------------------------------------------------------------------------- 1 | - 采样率（sample rate）的意思就是采样的频率。模拟（analog）信号要被电脑记录，就要数字化，方法就是对信号的电平（level）进行采样记录，记录的频率就是采样率。单位是Hz，意思是每秒采样的次数。 2 | 3 | ### 这张图错在哪里 4 | - ![图片](https://user-images.githubusercontent.com/42371034/218047432-ef12d590-9ba1-474b-b27b-838169ee8729.png) 5 | - 这张图错误的展示了采样的过程。 6 | - 他让读者认为，采样就像是在一个平面上记录了很多个点，在还原信号用于播放的时候，我们就用一条平滑的曲线把这些点连起来。也许一个中学数学课上的采样是这样的，但是这样的过程应该不会发生在由一堆工程师设计的数字音频产品里面。 7 | - 在讲述正确的采样过程之前，我还要描述一下别人是怎么误会这个采样过程的。注意，以下为错误言论： 8 | - 一般CD的采样率为44.1Khz. 也就是它每秒会记录44100次信号。对于一个44100Hz的正弦波信号来说，他的一个周期只对应了一次采样。（信号的周期是1/44100 秒,采样的时间间隔也是1/44100 秒）。示意图如下： 9 | - ![图片](https://user-images.githubusercontent.com/42371034/218050853-52769634-8e71-4bef-af31-f0b12fca5bef.png) 10 | - 如果一个周期内，信号只被采样了一次，也就是只确定了图上的任意一个点，请问能把这个信号正确采集然后正确回放出来吗。不行，对吧。 11 | - 设想以下极端情况，现在有一个20KHz的正弦信号需要被采样，采样率还是44100Hz，请问一个周期内被采样了几次呢？不用算了，告诉你答案，两次。 12 | - 关键的问题来了，如果已知一个正弦上任意两点的位置，我们能复原这个正弦信号吗？答案是不行。比如下图就演示了，两个不同的信号都经过了同样的点： 13 | - ![图片](https://user-images.githubusercontent.com/42371034/218053185-486efb32-ac93-4b49-a0b1-42e732100e67.png) 14 | - 只要一个反例就说明两个采样点不足以采样一个正弦信号。 15 | - 结论：20KHz的正弦信号不能被44100Hz的采样率正确采集。 16 | - 错误言论结束。 17 | - 如果你不知道上面的话错在那里，就请接着往下看。 18 | ### 数字音频的理论基础 1.傅里叶变换 19 | - 刚才讲理论已经很枯燥了，我在这里就不想讲了，反正我也不会。还是直接讲结论。 20 | - 不管信号是什么样子的，哪怕是这样子的： 21 | - 这不是乱画的，这是一个真实乐器的信号 22 | - ![图片](https://user-images.githubusercontent.com/42371034/218054584-0463aa69-dd3e-4558-b925-061e28c7bc83.png) 23 | - 这样的信号可以被分解为一系列正弦波的和。当然，不是某一种信号，而是任何信号都可以被分解为一系列正弦波。这也不是假设，而是在数学上证明了的。这样的分解就是傅里叶变换。 24 | - 这个理论告诉我们，采集信号，其实就是在采集正弦波，合成后的波形看起来不是正弦波没关系，测试采样的时候，只要能采集正弦信号（sine wave），那么就能采集任意信号。 25 | 26 | ### 数字音频的理论基础 2.采样定理 27 | - 采样定理说的是，对于任意已知正弦信号，只需要他频率一倍的采样率就可以完整采集。那么对于一个20KHz的正弦信号，需要40KHz的采样率就能完整采集。 28 | - 这不对啊。刚刚不是画图了吗，20KHz的信号，44100Hz的采样率（比40KHz还高了那么一点），一个周期两个采样点，采到的结果不能确定唯一一个信号啊。 29 | - 这里不是教科书，我还是直接放答案。那两个采样点能确定的正弦信号不唯一，但是在20KHz以内是唯一的。别的信号已经超过20KHz人类能听到的范围了，我们直接摒弃就行了。 30 | - 之所以现实中采样率不是40KHz而是高了一点就说明工程师们没有完全依赖理论，还多留了一点点余地，采到了高一点点的频率。 31 | ### 然后呢？ 32 | - 有人可能就要问了，两个采样点确定一个正弦曲线（当然带有频率上限）我明白了，但是这只是一个理论上的计算结果，我不认为喇叭只需要任意两个点就能播放一个正弦波出来。没错。 33 | - 所以采样到的数字信号还要经过计算的，把这两个采样点经过计算，还原成正弦信号，然后再播放。这才是现代数字音频完整的流程。这个计算的过程就是模拟数字转换的核心竞争力了，因为计算总归有误差的。贵的产品的误差要小很多。 34 | - 这时候再来看开头的那句话是不是就能理解了：这张图错误的展示了采样的过程。他让读者认为，采样就像是在一个平面上记录了很多个点，在还原信号用于播放的时候，我们就用一条平滑的曲线把这些点连起来。 35 | - 两个点，不管怎么连也不可能再现一个正弦曲线。而经过了计算，就可以100%精确还原正弦曲线。是绝对精确的完整信号，有数学表达式的那种，不是开头图片上看起来一格一格的不连续的信号。 36 | ### 实际上需要的音频采样率是多少 37 | - 按上面说的，40KHz就可以采集到最高20KHz的信号，我们应该就用40KHz的采样率吗？理论上是这样，但是实际上还是有一些问题，在这个采样最高频率附近会有一些失真之类的问题，所以一般把这个采样率设置在比40KHz高一些的地方，这就是CD标准的44.1KHz采样率的原因，后来DVD出现以后又把这个采样率提高了一点点，变成了48KHz。 38 | - 但是后来采样率就越来越失控了，在厂商的错误宣传和发烧友的追捧下，文章开头的图片广为流传，让人觉得采样率越高就会越接近原始信号，曲线就会越平滑。现在有了96KHz，甚至192KHz的采样率，我实在不知道这样做的意义何在。当然有很多人宣称他们能听到192KHz采样率音质多么的好，只能说我听不出来。 39 | - 不光我听不出来，很多业界的大佬也出来说高采样率不会带来更好的音质，其中就有数字音频ADC（模数转换器）三大厂牌之一的Larvy（其他两家是dCS和Prism sound），我看过他们老总亲自写的技术文章中提到了一个最基础的常识：人听不到超声波，不管高采样率的音乐听起来多么好听，他好听的地方一定不是20KHZ以上的频率带来的。（ 其他两家现在都因为盈利困难转做hifi发烧友的生意，自然不太敢说这些得罪发烧友的话，要是说了高采样率不好，自家的高采样率产品就没法卖了） 40 | ### 便宜的设备支持96KHz、192KHz，并不代表音质好 41 | - 现在应该不用我说，大家也知道，设备如果以支持高采样率为卖点，声称这代表高音质，自然是无稽之谈。 42 | - 真的有不少人以为设备支持高采样率就是高音质。哪怕很多声卡之类的其实很便宜也支持的，比很多贵得多的音质要差很多，但是就会有人拿来意淫这个高采样率能带来什么好处之类。 43 | ### 高采样率的坏处 44 | - 高采样率看起来似乎没有什么好处，但是也没有坏处啊。其实高采样率的坏处很大的。 45 | - 首先就是占用存储空间，当然现在存储空间对很多听音乐的人来说并不贵。但是对于录音的人就很贵了，毕竟3分钟的歌，录音文件可能要几个小时的。 46 | - 最大的问题就是，在采样和播放的时候，前面说了，结果是算出来的，这里面有巨大的运算量。这些运算对于一台电脑来说是不在话下的，但是对于一个CD机，一个声卡，一个小型播放机来说，他们就不会搭载电脑这么强的运算单元了吧，毕竟他们整台机子也只有电脑几分之一的价格，只有最高档的那些数字模拟转换器才会搭载强大的运算芯片。 47 | - 对于这些便宜的设备，运算48KHz的信号还算是可以勉强用，但是96KHz和192KHz一下就让运算量大了2倍，4倍。你猜会怎么解决呢？厂家会不会搭载一个具有4倍运算力的芯片给你呢？我只能说不会。 48 | - 那怎么解决呢？降低运算精度。这可比采样率的损失大多了。 49 | - 这也不是我瞎猜的，同样来自Larvy的技术文档，连业界最贵最顶级的厂商都承认了他们在高采样率下面会降低运算精度（虽然不是放在网站大大方方承认的，而是遮遮掩掩自己翻找才能看到的，总归是承认了），那些卖便宜货的厂商难道不会么。高运算精度不光是算力需求太大，而且电路发热也会很大。音频产品不同于电脑类的产品，音频信号在运算和处理时对电路的温度有比较高的要求，温度越高越容易在信号中产生噪音。 50 | - 仅仅是模拟信号到数字记录这一步就有这么大的负担，那么在录音软件里面对高采样率声音进行混音同样也是压力很大的，压力大了难保软件不会给你降低处理精度，就算没有降低处理精度，处理的速度和能做的处理也会大幅受限。就算软件不降低精度，速度慢了操纵软件的人总是会不耐烦的，（例如我以前）不耐烦了就少做一点，一般人可能也听不出来。这就是无形中的损失。 51 | - 最后放上Larvy的网址，供大家参考，也可以查询一下他们的东西属于什么级别的产品：https://lavryengineering.com/ 52 | -------------------------------------------------------------------------------- /频谱图怎么读.md: -------------------------------------------------------------------------------- 1 | ### 频谱图怎么读 2 | --------------------------------------------------------------------------------