How to install it in Ubuntu 18.04

[HongyuanChen]

I have some trouble in installing the packages in Ubuntu 18.04.
I have used the 'sudo add-apt-repository ppa:berndporr/dsp' in the terminal and nothing shows wrong or error.
But I can't find the folder '/usr/share/doc/iir1-dev/'

Here is what the terminal display when I use the 'sudo add-apt-repository ppa:berndporr/dsp'

' C++ classes for filtering signals
更多信息： https://launchpad.net/~berndporr/+archive/ubuntu/dsp
按 [ENTER] 继续或 Ctrl-c 取消安装。
命中:2 http://mirrors.aliyun.com/ubuntu bionic InRelease
命中:1 https://mirrors.sjtug.sjtu.edu.cn/ros/ubuntu bionic InRelease
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命中:8 https://dl.google.com/linux/chrome/deb stable InRelease
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获取:10 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed InRelease [242 kB]
命中:11 http://mirrors.aliyun.com/ubuntu bionic-backports InRelease
命中:12 http://ppa.launchpad.net/berndporr/dsp/ubuntu bionic InRelease
命中:13 http://mirrors.aliyun.com/ubuntu bionic-proposed InRelease
命中:14 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease
获取:15 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-security/main amd64 DEP-11 Metadata [55.2 kB]
获取:16 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-security/universe amd64 DEP-11 Metadata [61.0 kB]
获取:17 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-security/multiverse amd64 DEP-11 Metadata [2,464 B]
获取:18 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates/main i386 Packages [1,528 kB]
命中:19 http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu bionic InRelease
获取:20 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates/main amd64 Packages [2,724 kB]
获取:21 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates/main amd64 DEP-11 Metadata [297 kB]
获取:22 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates/universe amd64 DEP-11 Metadata [302 kB]
获取:23 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates/multiverse amd64 DEP-11 Metadata [2,468 B]
获取:24 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-backports/universe amd64 DEP-11 Metadata [9,268 B]
获取:25 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed/universe Sources [9,620 B]
获取:26 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed/main amd64 DEP-11 Metadata [3,172 B]
命中:27 https://apt.v2raya.org v2raya InRelease
获取:28 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed/universe i386 Packages [12.6 kB]
获取:29 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed/universe amd64 Packages [20.5 kB]
获取:30 http://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed/universe Translation-en [11.7 kB]
已下载 5,533 kB，耗时 2秒 (3,201 kB/s)
正在读取软件包列表... 完成'

[berndporr]

Thanks for reporting.
After you've added the repository you need to install the actual library and the development files with:

• Library files: sudo apt install iir1
• Development files: sudo apt install iir1-dev