Genesis:Audio Chip Notes
At the heart of the Genesis/Mega Drive's sound hardware is the Yamaha YM2612 FM synthesizer chip, which is descended from the YM2203 chip which Sega had used in numerous arcade games (i.e. Hang-On, Space Harrier, others). The YM2612 has six 4-operator FM synthesis channels, with the sixth channel capable of 8-bit PCM sample playback. Unlike the YM2203 and the YM2151 which Sega had also used in arcade hardware, the YM2612 also has a built-in stereo DAC (digital to analog converter), saving both motherboard space and production costs. Accompanying the YM2612 are four PSG audio channels (three square wave and one noise) which originate from the VDP. The PSG core used in the VDP is based on the Texas Instruments SN76489, and was also used in the Master System and SG-1000. In many Genesis games, the PSG is typically used for sound effects, but was also used to great effect in some games for lead and background melodies.
Quantization Noise aka "Ladder Effect"
The YM2612 has a peculiar flaw with its 9-bit DAC, which causes low volume sounds to be quantized in an unusual way and is especially apparent during fades. Some composers were highly aware of this design flaw and used it in their compositions, with Yuzo Koshiro in particular being a fan of the technique.[1]
YM3438
The YM3438 was an FM synthesizer chip introduced by Yamaha in 1990, and was marketed as an improved version of the YM2612. Unlike the YM2612, it uses CMOS logic which reduces power consumption and heat, and it also eliminated the