MIDI files holds instructions to sound cards in keyboard or computers. The MIDI data is so to speak the "recipe for the music", just like a music sheet is.
Audio files are samplings of music. Audio data is so to speak "the music".
The sound card is the "black box" which reads the recipe for the music; and then creates the audible music.
It has often been discussed if it was possible to reverse the process: Create MIDI data from Audio data.
To some degree it is possible. But the limits are quite constricting: Only single instrument MIDI data can be created from audio data.
Complex audio data (and audio data mostly is quite complex) can NOT be turned in usable MIDI data. For details read Convert from music WAV-MP3 to MIDI
To demonstrate this let us look at some analogies: "A rather simple sandwich" and "A rather complex dish".
Both cases starts with a recipe to the chef: Which ingredients to use.
Next comes the "black box": How to prepare and mix the ingredients; and how to bake or heat the meal.
Consider this recipe from here:
Mary's Plain Old Simple Ham and Cheese Sandwich
- 2 slices whole wheat bread
- 4 oz thinly sliced ham
- 2 oz sharp cheddar cheese
- 1/2 fresh tomato, sliced
- 1 tbs mayonnaise
- 1 tbs pesto
This rather simple recipe can be transformed into:
I think it is possible to tear the sandwich apart into ingredients. Most can be separated.
The cooking process can be reversed; at least mostly. But the toasting of the bread can not be reversed.
If the sandwich was not toasted, it could be transformed "backwards", i.e. into its ingredients.
Consider this recipe from here:
Beef Stew with Carrots & Potatoes
- 3 pounds boneless beef chuck (well-marbled), cut into 1½-inch pieces
- 2 teaspoons salt
- 1 teaspoon freshly ground black pepper
- 3 tablespoons olive oil
- 2 medium yellow onions, cut into 1-inch chunks
- 7 cloves garlic, peeled and smashed
- 2 tablespoons balsamic vinegar
- 1½ tablespoons tomato paste
- ¼ cup all-purpose flour
- 2 cups dry red wine
- 2 cups beef broth
- 2 cups water
- 1 bay leaf
- ½ teaspoon dried thyme
- 1½ teaspoons sugar
- 4 large carrots, peeled and cut into one-inch chunks on a diagonal
- 1 pound small white boiling potatoes (baby yukons), cut in half
- Fresh chopped parsley
This rather complex recipe can be transformed into:
I think it is NOT possible to tear the dish apart into ingredients.
The cooking process can NOT be reversed; not at all.
There is no way to get the 2 cups dry red wine back. Sorry, folks...
Rather simple audio files can be turned into MIDI data, while complex (read: multi instrument) audio files cannot.
Just like the sandwich can be transformed into its ingredient; while the dish cannot.