qtractor doesn't have any built-in sound generator, synth or instrumehnt whatsoever for you to get the MIDI tracks rendered to audio. you should provide one in the form of a MIDI instrument plugin, connect to an external soft-synth or even on outboard MIDI hardware.
i guess the same occurs with Muse, and Rosegarden, etc.
qtractor doesn't have any built-in sound generator, synth or instrumehnt whatsoever for you to get the MIDI tracks rendered to audio. you should provide one in the form of a MIDI instrument plugin, connect to an external soft-synth or even on outboard MIDI hardware.
i guess the same occurs with Muse, and Rosegarden, etc.
you have this qtractor MIDI howto if you still feel lost.
hth.
cheers