It's a more artistic and abstract way of referring to the physical material of sound, rather than simply "sound" itself. Here's how it's often used:
* In music: It can refer to the raw, unprocessed elements that a composer uses to create a piece: the instruments, the voices, the ambient noises, etc. It emphasizes the "stuff" of sound, rather than the melody, harmony, or rhythm.
* In sound design: It could describe the specific textures and timbres of sounds, the way they feel in space, or the way they interact with each other.
* In philosophy: "La matière sonore" can be used to explore the essence of sound itself, its physical properties, and how it exists in the world.
The phrase suggests a deeper, more analytical approach to sound, focusing on its physical properties and its potential for artistic manipulation.