YM2151

YM2151
Designer: Yamaha

The Yamaha YM2151, also known as the OPM (FM Operator Type-M), is an audio chip by Yamaha for performing frequency modulation (FM) synthesis. It was Yamaha's first single-chip FM synthesis implementation, being created originally for certain members of Yamaha's popular DX series of keyboards.

Usage

The YM2151 was used in many arcade boards, starting with Atari's Marble Madness board in 1984, and later being licensed for use by many other companies including Sega, Konami, Capcom, Data East Pinball, Irem, and Namco, as well as Williams Pinball, with its heaviest use in the mid-to-late 1980s. Some arcade developers, such as Eighting, continued to use the chip through the late 1990s, however. It was also used in the X1 and X68000 home computers.

This chip was also used in some Yamaha budget electric pianos, such as the YPR-7/8/9. It can also be found in the Yamaha SFG-01 and SFG-05 FM Sound Synthesizer Units. These are expansion units for MSX computers and were already built in some Yamaha MSX machines such as the Yamaha CX5M. It provides the FM synthesizer with stereo output jacks, MIDI ports and a connector for an external keyboard.

Some later SFG-05 modules also contained the YM2164 (a.k.a. OPP), which is identical to the YM2151 apart from some minor differences in control registers such as test registers and/or interrupt handling, which may break compatibility with some devices. The YM2164 was also used in Yamaha's FB-01 module (essentially a standalone SFG-05) and their DX21, DX27, and DX100 keyboards, as well as in IBM's Music Feature Card (MFC).

Design

The YM2151 implements FM synthesis, which consists of a number of operators connected in a variety of ways, with each operator consisting of a modified ADSR envelope, rate scaling, frequency multiplication, and detuning. It supplies up to eight voices, each having 4 operators (each with a sine-wave oscillator plus an envelope generator). 8 FM algorithms are available for sound generation, each of them using different arrangements of the 4 operators. The last operator of the last channel can be substituted for a variable-frequency noise channel.

FM Operator Type-M is a subtype of Yamaha's 4-operator FM synthesis used in most of Yamaha's 4-operator FM sound chips, and is nearly identical to that of OPN-based FM synthesis used in chips such as the YM2612 (OPN2). The main differences between it and the OPN series is that the OPM has, among others, a much more configurable LFO, a four-bit secondary detune, and a variable-frequency noise channel for the fourth operator on the eighth channel. It also does not have SSG-EG, a feature that is exclusive to the OPN series. The OPN series also has a "special FM3" mode that is not available on the OPM.

As such, the YM2151 is capable of reproducing sounds from the YM2612 (as well as other OPN-based chips) due to the close similarities between the two chips. The popular virtual instrument VOPM is, as the name suggests, a simulator of the YM2151, however it is also popular for simulating sounds from the YM2612 due to their aforementioned similarities. Likewise, the YM2612 can also simulate sounds from the YM2151 as well as other Yamaha 4-operator FM sound chips also (with some minor differences in the way the sound is produced), again due to their similarities.

Sound produced from the YM2151 is usually fed into a digital-to-analog (DAC) converter chip such as the YM3012 or YM3014, which converts the digital signals produced by the YM2151 into analog audio signals, producing the final output that can be heard by speakers.

Documentaton

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  Data sheet

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  Application manual