Sony · 1994 · 1990s · 24 voices
The PlayStation's Sound Processing Unit mixed 24 channels of compressed samples at CD quality, with hardware reverb — and sat beside a CD drive that could simply stream a recorded soundtrack instead.
The Sound Processing Unit in Sony's PlayStation marks the point at which console audio stopped being synthesis and became playback. It is a 16-bit sample player supporting up to 24 channels of ADPCM-compressed audio, with 512 KB of dedicated sound RAM and a sampling rate of up to 44.1 kHz — the same rate as an audio CD. In hardware it provides pitch modulation, envelopes, looping and, most audibly, digital reverb, which is why so many PlayStation soundtracks have the spacious, washed quality that separates them from the dry sound of 16-bit consoles. Composers typically drove it with MIDI-style sequences triggering their own sampled instruments, an approach that kept music small enough to live in memory alongside the rest of the game. But the SPU had a partner that changed what game music could be: the CD-ROM drive, which could play CD-DA audio directly. A developer could bypass the synthesis model entirely and stream fully produced, studio-recorded tracks — licensed electronic music, live instruments, vocals — with the drive doing the work. The PlayStation's audio identity is the product of that choice between the two paths, and many of its best soundtracks used both.