Digital signal processor (DSP)
A processor tuned to multiply and accumulate streams of samples in real time.
Nearly all signal processing — filters, FFTs, reverb — boils down to one operation: multiply a sample by a coefficient and add it to a running sum. A DSP does that, the MAC, in a single clock cycle, with separate memory buses for data and coefficients so both arrive at once. Add hardware circular buffers and zero-overhead loops, things a general-purpose CPU has to emulate with extra instructions.
Texas Instruments' TMS320 from 1983 made the category commercial, followed by Motorola's 56000 and Analog Devices' SHARC. Pro Tools built its studio dominance on cards packed with Motorola chips. Today ordinary CPUs with SIMD have taken over most of the music work, but DSPs still sit in every phone, earbud and audio interface with an onboard mixer.