Rarely will you need more than one instance of FluidSynth, because QSynth/FluidSynth together offer up to 256 independent input channels, and the ability to control the reverb and chorus effects independently by channel. The most common use of multiple FluidSynth instances is if you want to use multiple MIDI instruments. In other words, if you want to use multiple SoundFonts at the same time, you will need to use one instance of FluidSynth for each SoundFont.

Thankfully, Qsynth allows us to do this almost effortlessly! Each "instance" of FluidSynth is created and controlled by, in effect, running the FluidSynth synthesis application multiple times. The reality is that, since Qsynth controls the FluidSynth engine directly, it simply starts the synthesis engine directly, creating multiple instance of that engine. This is much more efficient than actually running Qsynth multiple time, or even than running FluidSynth directly from a terminal. Each such instance is represented in Qsynth by a "tab," displayed at the bottom of the Qsynth window.

To create an additional instance of FluidSynth:

Each instance of the FluidSynth engine has its own settings in the "Setup" window. Qsynth supports a theoretically unlimited number of FluidSynth instances, but your computer's memory will probably not allow many more than ten, depending on the SoundFonts used.