Yamaha YM2610B OPNB2: Advanced FM and ADPCM Sound Chip

Introduction

The Yamaha YM2610B, also known as OPNB2, is an advanced sound chip developed by Yamaha. It’s an enhanced version of the YM2610 (OPNB) and is part of Yamaha’s OPN family of FM synthesis chips.

Key Specifications

• Manufacturer: Yamaha Corporation
• Family: OPN (FM Operator Type-N)
• Primary Use: Neo Geo arcade and home video game systems
• FM Channels: 6 (increased from 4 in the original YM2610)
• Operators: 4 per FM channel

Features

• FM Synthesis: 6 concurrent FM channels with 4 operators each
• SSG: 3 square wave tone/noise channels (YM2149 compatible)
• ADPCM-A: 6 channels, fixed pitch, 18.5 kHz sampling rate at 12-bit from 4-bit data
• ADPCM-B: 1 channel, variable pitch, 2–55.5 kHz sampling rate at 16-bit from 4-bit data
• Timers: Two interval timers
• LFO: Low Frequency Oscillator for modulation effects

Improvements over YM2610

• Increased FM channels from 4 to 6, matching the capabilities of chips like the YM2612
• Retained all other features of the original YM2610, including ADPCM capabilities

Applications

The YM2610B was primarily used in:

• Later models of SNK’s Neo Geo arcade and home video game systems
• Potentially in other arcade game systems, though specific examples are not provided in the search results

Technical Details

• DAC: Used in conjunction with a YM3016 stereo DAC
• ADPCM Capabilities: Allows for high-quality sample playback alongside FM synthesis
• Compatibility: Likely backward compatible with YM2610 sound data

Legacy and Impact

• Enhanced the audio capabilities of later Neo Geo games
• Provided a balance between FM synthesis and sample playback
• Contributed to the distinctive sound of many arcade and Neo Geo home console games
• Represents an evolution in Yamaha’s sound chip technology

Conclusion

The Yamaha YM2610B OPNB2 stands as a significant advancement in sound chip technology, particularly for gaming applications. By increasing the number of FM channels while retaining the ADPCM capabilities of its predecessor, it offered game developers more flexibility in creating rich, complex soundtracks. Its use in the Neo Geo system helped define the audio aesthetic of many classic arcade and home console games of the 1990s.