gsequencer software package provides Advanced Gtk+ Sequencer audio processing engine, 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 gsequencer
gsequencer is installed in your system.
Make ensure the gsequencer package were installed using the commands given below,
$ sudo dpkg-query -l | grep gsequencer *
You will get with gsequencer package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Sound |
| Package | gsequencer |
| Version | 0.7.90-1 |
| Description | Advanced Gtk+ Sequencer audio processing engine |
| Sub Section | Sound |