Where Is All The Audio?
We have come to place music into two broad categories; those of New Music and that of Traditional Music. Music prior to turn of the century comes to be thought of as the original. This Traditional Music gets lumped together with what most people refer to as Classical. This classification can be so well fixed in people's minds that even traditional rock music is referred to as Classic Rock.
The so called Classical Music is really about three different periods that were all different in their practice. Having said that, there are some differences in the songs after the turn with the century that are distinctive enough to warrant the label of recent Music.
Prior to the turn in the century, all music was 'goal oriented' or 'tonal,' and therefore there was one chord within the particular composition which was the goal or resting point of the music's chord progression. Once this chord was reached, the music sounded finished and the music would not sound finished until this chord was reached. Hence this chord would show-up in the very end of the music but in addition at the ends coming from all phrases or melodies, virtually. It would not be the same chord for each and every piece of music but would depend on the 'key' of the music. That's the meaning of 'key.' If the piece of music is in the 'key of C,' then this chord it must end on is C. A piece in the 'key of G' would end on G and so on.
Well. after a millennium or so, composers got the itch to test something new and so look for the first examples of the newest Music. Claude Debussy has often been referred to as 'Father of Modern Music,' and his awesome works began to make tonality ambiguous by employing other types of scales such as the Whole Tone Scale.
Some composers went beyond this and tossed out tonality completely. The most notable example of this is the Serial Music composed by Arnold Schoenberg. Serial Music used a scale of twelve tones (instead of the traditional eight) and studiously avoided any note/chord relationship. A few other composers like John Cage created that which was called 'Chance Music,' the location where the notes in the piece were dependant on the throw of dice.
Meanwhile, as of this same time, jazz was being made. Jazz and Blues returned to tonality which has a vengeance. However there have been many other elements added that qualified this as Songs. The difference in instrumentation, using the electric guitar and the greatly expanded role from the drums were certainly stuff that had not gone on before and so the birth of jazz as well as development into the pop today certainly fits into the category of New Music.