Ricoh · 1983 · 1980s · 5 voices
The Ricoh 2A03 integrated the NES audio processing unit with a modified 6502 CPU on a single die, providing five sound channels whose characteristic square waves, triangle bass, and hissing noise defined the sonic identity of the 8-bit era.
The 2A03 (NTSC) and 2A07 (PAL) combined a modified MOS 6502 CPU with the audio processing unit on a single chip to reduce component count and cost. The APU provided two square-wave pulse channels with programmable duty cycle (12.5%, 25%, 50%, 75%) and volume envelope; one triangle channel for bass lines; one noise channel using a linear feedback shift register for percussion; and one delta PCM channel capable of 7-bit samples at up to 33 kHz from ROM data. Despite these five channels, NES composers achieved extraordinary variety by exploiting timing, envelope shapes, and the interaction between channels. The Famicom expansion port allowed cartridges to include additional audio hardware — Konami's VRC6 chip (Akumajo Densetsu, 1989) added three superior synthesis channels, producing audio quality the stock APU could not approach. Koji Kondo, Hirokazu Tanaka, and Nobuo Uematsu built their earliest landmark soundtracks on this hardware.