Depends on your soundcard and software.
Cheaper soundcards use a very primitive kind of Midi, which is
basically some artificial tones mixed together to sound like
"instruments".
Better soundcards use "wavetable", which uses actual samples of
real instruments to playback. It sounds more real, but is still far
from perfect. Some software uses wavefonts, something similar
wavetable, and more customisable.
But, no electronic instrument will ever sound like the real thing.
For example Woodwinds, there are basically three ranges, lower, mid
and upper (altosimmo and all that), all have different
characteristics.
This, and many other factors seperate electronic music from the
real thing.