Manufactured by Ricoh and based on the MOS Technology 6502. NTSC versions of the NES use the 2A03, which is run at 1.79 MHz. PAL versions used the 2A07 processor, which is identical to the 2A03 except that it runs at 1.66 MHz. Timing differences between NTSC & PAL versions are to ensure that the sound output is the same on either. There is no seperate soundchip. The APU, a PSG (programmable sound generator) integrated in the 2A03 is used to produce audio.
- Nesdev wiki:NES APU
- Wikipedia, Nintendo Entertainment System technical specifications, Audio
- 2A03 Synthesizer
- MIDIbox NES?
- Turn NES into synth
- greybox, a MIDI-controlled synthesizer that uses the 2A03s on-chip sound generator.
- FPGA Implementation of the NES Audio Processing Unit
- NESizer by Johan Fjeldtvedt, YouTube