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This chip was used in many home computers (ZX Spectrum, MSX, Amstrad CPC, Atari ST, etc.), video game consoles (Intellivision and Vectrex), arcade boards and even slot machines! It is a 3-channel square/noise/envelope sound generator. The chip’s powerful sound comes from the envelope… The AY-3-8914 variant was used in Intellivision, which is pretty much an AY with 4 level envelope volume per channel and different register format. Furnace is capable of doing software sample playback on AY-3-8910, where all 3 channels can play 4-bit PCM samples (at the cost of a very high CPU usage) and utilize CPU timer effects, providing all kinds of modulation (PWM and envelope distortion) effects, again at the cost of a higher CPU usage. Songs utilizing timer effects may not sound as intended after VGM export.

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Effects

  • 20xx: Set channel mode.
    • 0: square
    • 1: noise
    • 2: square and noise
    • 3: envelope
    • 4: envelope and square
    • 5: envelope and noise
    • 6: envelope and square and noise
    • 7: nothing
  • 21xx: Set noise frequency. Range is 0 to 1F.
  • 22xy: Set envelope mode.
    • x sets the envelope shape:
      • 0: \___ decay
      • 4: /___ attack once
      • 8: \\\\ saw
      • 9: \___ decay
      • A: \/\/ inverse obelisco
      • B: \¯¯¯ decay once
      • C: //// inverse saw
      • D: /¯¯¯ attack
      • E: /\/\ obelisco
      • F: /___ attack once
    • If y is 1 then the envelope will affect this channel.
  • 23xx: Set envelope period low byte.
  • 24xx: Set envelope period high byte.
  • 25xx: Slide envelope period up.
  • 26xx: Slide envelope period down.
  • 29xy: Enable auto-envelope mode.
    • In this mode the envelope period is set to the channel’s notes, multiplied by a fraction.
    • x is the numerator.
    • y is the denominator.
    • If x or y are 0 this will disable auto-envelope mode.
  • 2Cxx: Set timer period offset.
    • Bit 7 is the sign.
  • 2Exx: Write to I/O port A.
    • This changes the port’s mode to “write”. Make sure you have connected something to it.
  • 2Fxx: Write to I/O port B.
    • This changes the port’s mode to “write”. Make sure you have connected something to it.

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What is Obelisco?

It’s a name used for a spiky waveform that starts low. Its origin is a wavetable that comes in DefleMask that happens to be called Obelisco.

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AY Derivative Modes

AY-3-810 was an absurdly popular chip that was blessed with many third-party clones, licensed or not.
  • The AY-3-8914 variant was used in Intellivision, which is pretty much an 8910 with 4 level envelope volume per channel and different register format.
  • Yamaha YM2149 is an AY-3-8910 clone released in 1983. It’s almost identical to AY with minor differences being: higher hardware envelope step resolution (16 vs 32), half-clock mode when voltage level is low, much stronger DC offset and cleaner, but softer output.
  • Sunsoft 5B is a YM2149 clone with half-clock mode forced on.

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Chip Configuration

The following options are available in the Chip Manager window:
  • Clock rate: Sets the rate at which the chip will run.
  • Chip type: Changes the chip model.
    • AY-3-8910: The original model.
    • YM2149(F): Yamaha clone with higher envelope resolution and a different volume curve.
    • Sunsoft 5B: A special model found in one of Sunsoft’s Famicom cartridges.
    • AY-3-8914: Scrambled registers. Has envelope volume control.
  • Stereo: Enable stereo output. Channel 1 is output left, channel 2 is output center and channel 3 is output right.
    • Separation: Allows you to set left/right separation.
  • Half Clock divider: Pulls the half clock pin, running the chip at half the speed.
    • Only available in YM2149.

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