Software-defined audio moves processing from fixed-function hardware chips to software running on general-purpose processors. This allows: continuous improvement through firmware updates, new features without hardware replacement, and user customization that was impossible with hardware-defined systems.
Examples: modern audio interfaces (Scarlett 4th Gen auto-gain and clip-safe features are software-controlled), active speakers with DSP (Genelec SAM, Neumann KH DSP), and wireless headphones (Sony/Bose ANC algorithms updated through firmware). The trend is toward more software control and less fixed hardware function.