Which inventor (or invention) has affected music the most? Interesting question. (Perhaps I should point out that my perspective is that of the traditional acoustic musician, not of the electronic musician.)
Even Tempered Tuning
This was my first idea for the most important innovation. It is a system which allows music to modulate between unrelated keys (tonal centres), and without it, much modern music simply wouldn't exist. It is thought to have been invented by Vincenzo Galilei (father of Galileo), and the first great exponent of its use was J.S. Bach.
There is no doubt that the equal temperament scale had great impact on western music : much of the harmonic fundamentals of popular music arise directly from the classical tradition, so we are not only talking about classical music here. However, much folk and other music is largely untouched by it. Also, it only affects the harmonic side of things, and not rhythmic or other aspects of musical development.
Revolutionary as even tempered tuning idea has been, I think that there is another, more recent, innovation which changed music more deeply.
Ways of passing music on
Perhaps the most important process in music-making is not directly related to playing - it is the way that music is communicated across time and space. Even the greatest musician must "stand on the shoulders of giants". Therefore, whose shoulders they get to stand on and how, is crucial.
Until the early 20th century, there were really only two ways by which compositions could be passed on.
The Aural Tradition
This means "learning by listening". Tunes, playing techniques and styles are passed down from teacher to student by demonstration, often over many generations. The master plays, the student listens, copies, remembers.
It is most common in various folk traditions. Sometimes, stories or spiritual beliefs are involved; for instance, in the Indian 'dhrupad' tradition, different strikes on some percussion instruments are linked to chanted syllables. The syllables combine into 'sentences' which reflect complex rhythmic structures. The sentences are also considered to be prayers to various deities. (Music, song, and speech are linked in a very natural relationship.)
The aural tradition tends to result in local styles developing within a genre (for instance, in Irish traditional music, fiddlers from Clare play very differently to those from Sligo). Sometimes, a certain family might develop their own style. The length of pieces that are be taught tends to be short. In genres which rely on the aural tradition, when longer pieces may be performed, they tend to be constructed from a somewhat improvisational approach, with the whole being made up from shorter fragments learned individually. As a result, musical form tends to be fairly simple.
Written Notation
The second available method of "passing it on" was the writing down of music. The western system of using a stave with notes as dots is still the dominant method (though others exist). The European classical tradition has been built around this, and it has resulted in compositions of great length and complexity. The development, for instance, of sonata form would have been difficult or impossible without notation.
Some aspects of music, however, are almost impossible to represent visually. Small variations of rhythm, pitch, volume and tone are inevitable between performers, but cannot be written.
In "classical" music, the use of expressive notation (special symbols and descriptive words) has evolved to try to address this. In the romantic and later periods, composers often included many instructions about dynamics and expression. Even so, different performances of the same piece can vary hugely in character.
(Much of Bach's work was written with almost no expressive markings, and often the only clue about tempo and mood would be the title, like 'Gavotte', a type of dance popular at the time. Of course, this has not stopped later editors from adding many expression marks, although with what authority is debatable.)
Several things seem to be an indirect consequence of the use of written notation. One is that the separation between the performer and the composer increases, as each job becomes more specialist and demanding. Also, there seems to be a tendency for the musical ideas to become more mathematical and abstracted, as the composition is done more with the visual parts of the brain, rather than being heard and then written. It encourages an idea of music in which each note is reduced to a mathematical entity, the extreme of which is seen in the work of some 20th century composers. (Whether or not this is a good thing is of course dependent on taste. Luckily, music is a broad church.)
In the twentieth century, however, another way to learn music became available.
Sound Recording
In 1888, the American Inventor
Thomas Edison patented a method to record and reproduce sound. By the 1920s, commercial musical recordings were becoming popular in the United States and elsewhere, and a path for powerful musical cross fertilisation between peoples and cultures was created.
The use of recordings as a way of learning has many advantages:
- there is no problem about recording tiny details of expression and style.
- there is no real limit to the length and complexity of the piece.
- the process of learning directly from a recording tends to develop the ear and encourage virtuosity.
It is no coincidence that in America, when commercial sound recordings became commonplace, musical improvisation developed into a sophisticated art. Jazz musician Louis Armstrong was one of the first superstars, obtaining Hendrix-like status in 1920s Harlem, and later generations built on his considerable achievements. They also influenced other musical traditions. For instance, saxophonist Charlie Parker, founder of the bebop school of playing owned many Lester Young records, many of which he had learned note for note. He also influenced and was influenced by the great Igor Stravinsky. (The two men met and clearly admired one and another.)
Later, as the blues and jump music of New Orleans developed into rhythm and blues, with artists like Fats Domino making hugely popular recordings. These travelled far and wide, for instance to Jamaica where the sound morphed into bluebeat and ska, and later to reggae. At the same time, young British artists like Peter Green and The Beatles heard the electric blues that was coming out of Chicago, and took it in their own direction.
How could this have happened without those ubiquitous discs of vinyl?
Even in non-american music, the effects are tangible. There are 1920s and 1930s recordings of Irish traditional musicians playing (mostly in the US, notably Chicago, because that's where the equipment to do it was). Comparison of these with modern Irish musicians shows a clear influence of swing and a brighter, more modern rhythmic conception, even on musicians who consider themselves quite pure within that genre.
In many ways, sound recording is the perfect fusion of the oral tradition and notation, as a method of carrying the message of music. It allows anyone with a recording of a given musician or composer to study his or her work at their leisure, regardless of when and where they lived, and in complete detail. I have no doubt that its invention by Mr Edison has influenced the development of the artform more than anything else.
Afternote: Later, the availability of recorded music had another marked effect. As it became more and more common in bars, and then was also used for dancing, life became tougher for the ordinary working musician. Live music in public went from being the norm to something of a special event, and these days, the musician who makes a full living from public performance is something of a rarity.
References:
1. wikipedia article on equal temperament
2. ditto for Sound Recording
3. "Really The Blues" - Mezz Mezzrow's autobiography, and a fascinating account of life in New York during 'the jazz age'.
4. Bird plays for Stravinsky
5. Many musical recordings.
6. Personal experience, particularly of working with other musicians.