Polyphone is an multiplatform and open-source soundfont editor for creating musical instruments.

• editing of sf2, sf3, sfz and sfArk file formats
• compatible with Jack and ASIO audio servers
• built-in synthesizer, controlled by a virtual keyboard or MIDI signals
• automatic recognition of root keys
• automatic loop of samples
• simultaneous editing of parameters
• specific tools for musical instrument creation
• recorder to keep a trace of what is played in a .wav file
• soundfont browser connected to the online repository

Check this page to find installers for your system.

See the documentation and forum.