68 lines
3.3 KiB
Plaintext
68 lines
3.3 KiB
Plaintext
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FCE Ultra General User's FAQ
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preliminary version
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Last updated on: Friday 13th, 2003
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Q: Why do some games make a popping sound(Rad Racer 2, Final Fantasy 3)?
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A: These games do a very crude drum imitation by causing a large jump in
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the output level for a short period of time via the register at $4011.
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The analog filters on a real NES and Famicom make it sound rather decent.
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I have not completely emulated these filters. Enabling high-quality
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sound emulation will also make these pseudo-drums sound better. See
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the next question for more information.
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Q: Why do some games' digitized sounds sound too loud?
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Why do the drums in Crystalis and other games sound fuzzy?
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A: The NES' digital to analog converter is faulty, in that it does not output
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sound linearly. This effect is most noteable when a games messes with
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register $4011, which is added with the triangle wave channel and the noise
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channel outputs. When $4011 is set to a large value, the volume
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of the triangle wave channel and the noise channel drop significantly. More
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Importantly, when digitized sounds are being played and the digitized sample
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stream is at a high value, less changes will be noticeable. In other words,
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the byte sequence "00 01 00" would be much more audible than the sequence
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"7e 7f 7e". This non-linearity is only emulated when high-quality sound
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emulation is enabled.
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Q: Why doesn't the NSF <insert name here> work(correctly) on FCE Ultra?
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A: Some NSF rips are bad. Some read from addresses that are not specified
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in the NSF specifications, expecting certain values to be returned.
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Others execute undocumented instructions that have no affect on
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less-accurate software NSF players, but will cause problems on NSF players
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that emulate these instructions. Also, the playback rate specified
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in the NSF header is currently ignored, though I haven't encountered
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any problems in doing this.
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Q: Why doesn't the game <insert name here> work(correctly) on FCE Ultra?
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A: Many factors can make a game not work on FCE Ultra:
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- If the ROM image is in the iNES format(typically files that have
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the extension "nes"), its header may be incorrect. This
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incorrectness may also be because of garbage in the
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header. Certain utilities used to put text in the reserved
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bytes of the iNES header, then those reserved bytes were
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later assigned functions. FCE Ultra recognizes and
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automatically removes(from the ROM image in RAM, not on the
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storage medium) SOME header junk.
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If the game has graphical errors while scrolling, chances are
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the mirroring is set incorrectly in the header.
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You can try to edit the header with a utility(in the NES
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utilities section at http://zophar.net ) or a hex editor.
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- The on-cart hardware the game uses may not be emulated
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correctly.
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- Limitations of the ROM image format may prevent a game from
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being emulated correctly without special code to recognize that
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game. This occurs quite often with many Koei MMC5(iNES mapper 5)
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and MMC1(iNES mapper 1) games in the iNES format. FCE Ultra identifies
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and emulates some of these games based on the ROM CRC32 value.
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- The ROM image may be encrypted. The author of SMYNES seems to
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have done this intentionally to block other emulators from
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playing "SMYNES only" games.
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