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Stupid laptop prematurely published before I was done - Undid revision 1229995088 by 76.14.159.1 (talk)
→Yamaha YM3438: Oh, no it doesn't improve the dynamic range. In fact, the YM3438 datasheet specifically mentions that loud sounds can cause distortion. Also, the YM3438 still has the low volume distortion issue, it's just much quieter relative to the YM2612. Effectively, the YM3438 has improved signal-to-noise ratio, not dynamic range.
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==== Yamaha YM3438 ====
==== Yamaha YM3438 ====
The '''YM3438''',{{r|YM3438}} a.k.a. '''OPN2C''', is a modified [[CMOS]] version of the YM2612, commonly used in Sega's [[List of Sega arcade system boards|arcade system boards]]. This version has an improved built-in DAC that fixed the low volume distortion bug that was present in the YM2612 while also improving the dynamic range of the DAC to prevent [[Clipping (audio)|clipping]] at very high volumes. It is not a direct, drop-in replacement for the YM2612 however, as the sound outputs have higher impedance.
The '''YM3438''',{{r|YM3438}} a.k.a. '''OPN2C''', is a modified [[CMOS]] version of the YM2612, commonly used in Sega's [[List of Sega arcade system boards|arcade system boards]]. This version has an improved built-in DAC that reduces, but doesn't completely eliminate the low volume distortion. It is not a direct, drop-in replacement for the YM2612 however, as the sound outputs have higher impedance.


==== Yamaha YMF276 ====
==== Yamaha YMF276 ====

Revision as of 23:06, 19 June 2024

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 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] It was also available in CMOS form as the YM3438, a.k.a. OPN2C.[1]

As with the YM3438, it was used by Sega in various arcade game systems, including the Mega-Play, Sega System C and Sega System 32, with the YM3438 being integrated into an ASIC in later models of the Mega Drive/Genesis.

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 additional FM channels and integrating a stereo output DAC.[1] The YM2612 removes the SSG component (although retaining its envelope generators) and GPIO ports found in the YM2203, YM2608 and YM2610.[1] While the YM2612 was mostly based on the YM2203, it was often referred to as being based on the YM2608 due to a number of similarities between the two sound chips, only lacking the latter's ADPCM channels among other aforementioned changes.

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]

Low volume distortion of the built-in DAC

An example of the low volume distortion created by the peculiar qualities of the YM2612's built-in DAC. This sample is from the Mega Drive game Beyond Oasis.
In some cases, this low volume 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.

Due to an error with the amplitude voltage in the original chip design, a peculiar form of crossover distortion known as low volume distortion (and historically known as the "ladder effect" or "TDM distortion") is introduced in the output. Any output that is sufficiently low in volume undergoes an exaggerated quantization, including any usage of fades in video game music. Some early Mega Drive/Genesis games such as After Burner II had their music written around this distortion, and as a result, the music sounds too quiet on later Mega Drive/Genesis consoles that uses the integrated YM3438 chip on the ASIC. Also, 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]

In recent years, the low volume distortion bug in the YM2612 has been successfully emulated in software and has been implemented as a feature in many Mega Drive/Genesis emulators since. Other variants of the YM2612 that have fixed the low volume distortion bug such as the YM3438 are also emulated and have been implemented in many Mega Drive/Genesis emulators as well.

Variants

Yamaha YM3438

The YM3438,[1] a.k.a. OPN2C, is a modified CMOS version of the YM2612, commonly used in Sega's arcade system boards. This version has an improved built-in DAC that reduces, but doesn't completely eliminate the low volume distortion. 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-powered 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 like most other Yamaha FM chips. The YM3433 external DAC chip was made specifically for the YMF276.

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

The YM3438 core was integrated in custom ASICs[6] used in the final revision of the Model 1 version and most revisions of the Model 2 version of the Sega Mega Drive/Genesis, as well as the Genesis 3 released by Majesco.

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, most notably Yuzo Koshiro.[4][7]

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.
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