alsa-source software package provides ALSA driver sources, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install alsa-source
alsa-source is installed in your system.
Make ensure the alsa-source package were installed using the commands given below,
$ sudo dpkg-query -l | grep alsa-source *
You will get with alsa-source package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | Sound |
| Package | alsa-source |
| Version | 1.0.25+dfsg-0ubuntu5 |
| Description | ALSA driver sources |
| Sub Section | Sound |