Understanding the difference between MIDI and Digital Audio

It’s always hard at first, for those not familiar with the concepts and technology involved, to explain why it is not possible to take your favourite music CD, pop it into the computer, and extract out the music notes. It’s one thing to tell folks that MIDI files, from which scores may be printed out, contains control data while digital audio files are bit representations of sound and thus not quite the same thing. Most often, if one attempts to explain this sort of thing, one is faced with blank stares. However, if one draws analogies from everyday life, there is a greater possibility of being understood. More specifically, try explaining our initial problem like this: you know how you need eggs, flour, milk and sugar to bake a cake. Well, supposing I give you that delicious cake and ask you to extract the eggs, flour, milk and sugar from it…. Impossible? But if I give you a recipe book, you’ll be able to bake me another cake just like the first one, using fresh ingredients. Think of your CD recording as that cake. It sounds right and all the ingredients are there, but they’re quite impossible to extract from the end product. MIDI information on the other hand is like your recipe book. It contains the information you need to make the cake, but it isn’t the cake itself. In the same way that you can’t pop your cake into some magical device and get back all the original ingredients or even the recipe, there’s no way you can pop in your music CD and get back the music notation from it.