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Author Topic: (GB) Noise channel is inaccurate  (Read 4843 times)

Offline DevEd

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(GB) Noise channel is inaccurate
« on: October 17, 2014, 05:17:15 pm »
This is an issue that's been bugging me for a VERY long time, but I only bothered mentioning it now. When it comes to sound, I need to have 100% accurate emulation at all times, period. Unfortunately, Deflemask does not have such accuracy when it comes to the noise channel. The other three channels are OK (not counting the fact that the wave channel is too quiet), but the noise channel is completely wrong. Here are some of the issues I was able to find with the noise channel:
• The RNG is wrong. See here for a detailed explanation of how it's SUPPOSED to work.
• Setting the volume does not work properly. If the volume is F and you keep decrementing it, then A) the volume does not actually change until it reaches 7, and B) the RNG changes depending on the current volume. On hardware, the RNG never changes, and if the volume is decremented or incremented by 1, then it changes as you would expect it to.
• The note range is too low when compared to hardware. There are a few games that use high-pitched noise for cymbals and sometimes even sound effects, and attempting to play such a note will cause the noise channel to play with the highest available frequency instead, which sounds really bad. See this video for an example of what I'm talking about.

Attached is a test I made which plays every possible note on the noise channel at every possible volume with both noise modes. There are two versions of it, one version is a direct-from-Deflemask WAV recording, the other is a .GB export.

And for the love of God, PLEASE DO NOT USE VISUALBOYADVANCE TO PLAY THE EXPORTED VERSION. Instead use bgb, Gambatte, or, y'know, an actual Game Boy with a flash cartridge. The reason I don't want you using VisualBoyAdvance  to play the exported version is because VisualBoyAdvance has the exact same problems Deflemask does. bgb and Gambatte both have 100% accurate noise channel emulation.

Offline Delek

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(GB) Noise channel is inaccurate
« Reply #1 on: October 17, 2014, 06:40:05 pm »
Hmmm, let's see how much of this points are DefleMask related issues or Emulation related issues.

Offline DevEd

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(GB) Noise channel is inaccurate
« Reply #2 on: October 17, 2014, 08:09:44 pm »
I'm assuming that this particular issue is emulation-related.

Now, I'm not saying I know anything about the GB/GBC hardware, I'm just saying I know how it SHOULD sound like.
« Last Edit: October 17, 2014, 08:13:07 pm by DevEd »