Despite its small size, StudioFactory (also known as SynFactory II) is a worthy and very complete audio studio where you can work with all kinds of audios, being very manageable and intuitive to work on its interface.
StudioFactory allows you to work with MIDI files, treat them, edit them and make modifications, coming equipped with your own keyboard to generate your own MIDI files, as well as being able to add sound effects and be able to mix two different MP3 files with each other in a single resulting file.
In addition, StudioFactory is free and hardly consumes system resources, making it ideal for not very powerful computers.
You can free download StudioFactory 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.