gxtuner software package provides Tuner for Jack, 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 gxtuner
gxtuner is installed in your system.
Make ensure the gxtuner package were installed using the commands given below,
$ sudo dpkg-query -l | grep gxtuner *
You will get with gxtuner package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Sound |
| Package | gxtuner |
| Version | 2.3~repack1-1 |
| Description | Tuner for Jack |
| Sub Section | Sound |