Every period and every style has its own sound; it arises automatically, according to the manner of writing in fashion. Conversely, the composer may consciously seek those instrumental or vocal resources best suited to the realisation of his tonal ideal. In a continuous interaction between these two quantities, the classical orchestra expanded to become its romantic equivalent. A first notable change was a gradual increase in the number of instruments. Each individual group became larger, with three to four players to a part, and new colours were introduced: the piccolo, cor anglais, bass clarinet, double bassoon, saxophone, Wagner tuba, celesta and a certain amount of percussion all made their entry. The clarity of the classical orchestra was replaced by a more flaccid sound, nonetheless accompanied by an unprecedented increase in the range of timbre. The art of orchestration became a study in its own right, and manuals on the theory of instrumentation appeared, the best of which offered refined thought on the handling of this enormous orchestral machine. Precisely because the romantics wished to attach a subjective-emotional value to timbre, great craftsmanship was required to master these new resources, even though the superficial observer may sometimes be inclined to assume the opposite.

And so we approach the years around 1900. The mastery of orchestral colour was passed on to modern composers, but the style changed, and insights into orchestration changed with it. On the one hand a reaction to romantic excess arose, manifest in a renewed preference for lucid, chamber music-like scoring, while on the other hand the expressionists – the direct offspring of German-romantic subjectivism – developed a completely different style of composition. Both groups sought to liberate timbre as a colouristic means and relate it to structure, an aim which can be attained with both large and small orchestras. The result in both groups was that the sound that had previously blended now became divided. For romantic orchestration was entirely based on a tonal concept that automatically produced a high degree of blend. The disintegration of tonality likewise resulted in the division of the sound. Characteristic differences included the following: with or without polyphonic tendencies the romantic-tonal style remained embedded in a homogeneous triadic structure; it was this verticality which brought about the typical system of instrumental doubling that formed the basis of romantic orchestration.