Support K054539? about mml2vgm

[SaxxonPike]

You make a good point. So, I have contributed my changes to mame. They are now merged. I hope you can find this useful.

mamedev/mame#9778

Gonna throw in a quick warning that the current emulation of the 054539 chip has it's flaws tho.
Namely, the 4-bit DPCM decoding appears to be incorrect, resulting in artifacts in DPCM samples. (8-bit and 16-bit PCM samples appear to be fine)
Additionally, the Echo/Reverb isn't emulated either.

May be probably best to disallow using the Reverb and 4-bit DPCM samples until the emulation in those two aspects has improved.

[musicalman]

Thanks for the heads-up!
I've heard some truly horrible dpcm emulation with this chip, but vgmplay doesn't give me anything nearly that awful. Whether it's accurate or not I don't know.
In vgmplay some tracks have echo/reverb applied but the echo appears pitch shifted down an octave. MDPlayer does the same, so I wouldn't doubt it's weird atm.
In any case, mml2vgm doesn't support dpcm or reverb on similar chips yet, so omitting these features wouldn't be a big issue for me.

[kuma4649]

OPXが残念な状態なので、あまり気が進まないですね。。。

[musicalman]

混乱しています。K054539のエミュレーションはOPXのように未熟だとおっしゃるのですか？

[kuma4649]

そういうことです。
気が向いたらサポートしますｗ

[musicalman]

ああ、私はエミュレーションが悪かったことを知りませんでした。
私はそれを使うことに興奮しました。 しかし、私はあなたが快適に感じていないかどうかを理解しています。

[SaxxonPike]

Hello! I just happened to find your project while searching for K054539 filter info while I improve the DPCM support in MAME.

You may use this table of deltas for your own K054539 emulation, which I have found to be more correct and do not result in a DC offset in samples I have tried:
{ 0, 1, 2, 4, 8, 16, 32, 64, 0, -64, -32, -16, -8, -4, -2, -1 }

As for reverb, it's probably a FIR filter (like the SPC700) but we do not know the taps for it yet.

[kuma4649]

こんばんは。申し訳ありません。
音源chipの対応は基本的にvgmplayか、mameの対応を待ってそれに合わせてこちらも移植しています。
ですので、ご提案はありがたいのですが、mameの開発チームに向けていただいたほうが良いです。