Assuming the notes are in the synth's playable range. it is very likely data related. There is a problem with some 3rd party MIDI files and Cakewalk sfz engine synths like the Studio Instrument series. Once the synth encounters unexpected data, the sfz engine shuts down and will not make any sound until the project is restarted. There are two ways to deal with this: Clean up the data. Open the Event List View and remove the data before the first note (CCs are OK too). Usuall