audio-mixer software package provides virtual package provided by aumix-gtk, alsa-utils-udeb, aumix, alsa-utils, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install audio-mixer
audio-mixer is installed in your system.
Make ensure the audio-mixer package were installed using the commands given below,
$ sudo dpkg-query -l | grep audio-mixer*
You will get with audio-mixer package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | audio-mixer |
| Version | |
| Description | virtual package provided by aumix-gtk, alsa-utils-udeb, aumix, alsa-utils |
| Sub Section | Virtual |