The default software synthesizer in One Man Band is JmSynth, a low latency version of the Microsoft synthesizer (Quicktime synth on the Mac). There are many other software synthesizers available on the market.
Most commercial synthesizers can be used stand-alone, to connect such a synthesizer to OMB you must use a virtual MIDI cable like e.g. LoopBe1 for Windows or IAC that is part of OSX (Application>Utilities>Audio MIDI Setup>MIDI Devices). Once installed the virtual MIDI cable can be selected in the Preferences window.
To use Soundfonts, VST, DXi and AudioUnits, you need a stand alone synth that is able to play these and connect that synth to OMB.
An example of how to install a free VST host in Windows and connect it to OMB with a virtual MIDI cable:
Download and install LoopBe1 and VSTHOST. Select LoopBe1 as MIDI Out in OMB.
Run vsthost.exe, select menu Devices>Midi>MidiInputDevices>LoopBe, select menu File>NewPlugin>(name of VSTi dll file), select menu Devices>Wave>buffer=441.
To reach the editor window of the VSTi in VSTHOST, click on the small window with the name of the VSTi and select menu PlugIn>Window>Edit.
The settings will be saved and the next time you start OMB you just need to start VSTHOST too.
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