Yamaha YM2612

From Justapedia, unleashing the power of collective wisdom
(Redirected from Yamaha YM3438)
Jump to navigation Jump to search
Yamaha YM2612

The YM2612, a.k.a. OPN2, is a sound chip developed by Yamaha. It is a member of Yamaha's OPN family of FM synthesis chips, and is derived from the YM2203.[1]

The YM2612 is a six-channel FM synthesizer. It was used in several game and computer systems, most notably in Sega's Mega Drive/Genesis video game console[2] as well as Fujitsu's FM Towns computer series.[3]

As with the YM3438, it was used by Sega in various arcade game systems, including the Mega-Play and Sega System 32.

Features

The YM2612 has the following features:[1]

  • Six concurrent FM synthesis channels (voices)
  • Four operators per channel[4]
  • Two interval timers
  • A sine-wave low frequency oscillator
  • Integrated stereo output digital-to-analog converter (most other contemporary Yamaha FM chips require a separate external D/A converter chip)
  • Per-channel programmable stereo sound (left, right, or both left and right resulting in centre)
  • For channel three, operator frequencies can be set independently, making dissonant harmonics possible. (Normally, they would have a simple relation like e.g. 2× or 3× relative to a common base frequency)

Technical details

The YM2612's FM synthesis block is an extended version of the FM block featured in the YM2203, adding three FM channels and integrating a stereo output DAC.[1] The YM2612 removes the SSG component and I/O ports found in the YM2203, YM2608 and YM2610.[1] It was also available in CMOS form as the YM3438, a.k.a. OPN2C.[1]

Whereas the high-end OPN chips such as the YM2608 have dedicated ADPCM channels for playing sampled audio, the YM2612 does not. However, its sixth channel can act as a basic PCM channel by means of the 'DAC Enable' register, disabling FM output for that channel but allowing it to play 8-bit pulse-code modulation sound samples.[1] Unlike the other OPNs with ADPCM, the YM2612 does not provide any timing or buffering of samples, so all frequency control and buffering must be done in software by the host processor.[2]

Output DAC peculiarities

File:Evil Territory YM2612 DAC Distortion.ogg
An example (from the Mega Drive game Beyond Oasis) of the crossover distortion created by the peculiar qualities of the YM2612's built-in DAC.
File:YM2612 TDM Distortion Example.ogg
In some cases, the crossover distortion can affect the loudness, and to some degree the timbres, of certain sounds. This sample is from the Mega Drive game Streets of Rage 2.

Unlike most Yamaha FM chips which require an external floating-point DAC, the YM2612 features a built-in 9-bit DAC, which uses time-division multiplexing to play one sample of each channel in sequence, similar to the YM2413.[citation needed] Due to an error with the amplitude voltage in the original chip design, a peculiar form of crossover distortion is introduced in the output. Additionally, because of the reduced dynamic range of the built-in DAC, additional distortion may be generated when playing sounds with a very high volume.[1]

Variants

Yamaha YM3438

The YM3438,[1] a.k.a. OPN2C, is a modified CMOS version of the YM2612. This version has an improved built-in DAC that reduced the peculiar crossover distortions caused by the amplitude voltage errors present in the YM2612. It is not a direct, drop-in replacement for the YM2612 however, as the sound outputs have higher impedance.

Yamaha YMF276

The YMF276,[5] a.k.a. OPN2L, is a low-power version of the YM3438, used in the Fujitsu FM Towns II. It came in a smaller 24-pin SOP package. Unlike the YM2612 and YM3438, the YMF276 requires an external DAC chip. For this reason, the YM3433 was designed specifically for this version.

Sega Mega Drive/Genesis ASICs made by Yamaha (FC1004, FF1004, FJ3002 and FQ8007)

The YM3438 core was integrated in custom ASICs[6] used in most revisions of the Model 2 version of the Sega Mega Drive/Genesis.

Game audio

Used in conjunction with the Texas Instruments SN76489 PSG as the main sound generators of the Sega Mega Drive/Genesis console, the YM2612 was prominently utilized by numerous prolific video game music composers, such as Yuzo Koshiro.[4][7]

Other uses

In 2020, the company Twisted Electrons released the MEGAfm, a desktop synthesizer module that uses two YM2612 chips.[8]

A VST, AU and AAX and Reason Studios Rack Extension plugin called RYM2612 was made by Inphonik. This includes cycle accurate envelopes and quirks of the original chip.[9] They also offer a free sample and bitrate reduction plugin, the PCM2612, that emulates the timbre of the original chip playing a sample through the DAC channel.[10]

See also

References

  1. ^ a b c d e f g h YM3438 Application Manual (Japanese)
  2. ^ a b Sega Genesis Technical Manual - YM2612 section (updated with errors corrected)
  3. ^ Purcaru, Bogdan Ion (13 March 2014). Games vs. Hardware. The History of PC video games: The 80's. p. 527. Retrieved 14 December 2017.
  4. ^ a b "Super Sonic: Creating the new sound of Sega's hedgehog hit". TheGuardian.com. 13 February 2020.
  5. ^ Undocumented Sound Chips - Yamaha YMF276
  6. ^ Sega Genesis 2 / Sega Mega Drive II Service Manual
  7. ^ "Sega Mega Drive Mini review – a legacy truly honoured". TheGuardian.com. 19 September 2019.
  8. ^ "MEGAfm".
  9. ^ "RYM2612 Iconic FM Synthesizer | Inphonik".
  10. ^ "PCM2612 Retro Decimator Unit | Inphonik".

External links

Retrieved from "https://justapedia.org/index.php?title=Yamaha_YM2612&oldid=1118581578#Yamaha_YM3438"