Sound emulation in Panasonic FS-A1WX MSX2+ machine with turbo

By santiontanon

Paladin (787)

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11-04-2017, 00:58


As reported by wyrdwad in this thread ( ), it seems that when the turbo is activated in Panasonic FS-A1WX MSX2+ machines, the frequency of the sounds made by the PSG seems to also be increased. I was trying to program a fix for that issue in Tales of Popolon, but in OpenMSX such frequency increase does not happen. I was just wondering if this is an unemulated feature, or if that might just be happening in some machines and not in others?

Thanks in advance! :)

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By Meits

Scribe (5398)

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11-04-2017, 02:31

This happens to all Panasonic MSX2+ machines. And since the frequency is not exactly multiplied by two, the pitch is out of tune if you play music that supports both FM/SCC and PSG. Microcabin and Konami games suffer this issue quite a lot.
But at least the tone is clean, just higher.
This can not be said of the turbo 7MHz kits (at least the ones around here in Holland) as they switch back to 3.5MHz a lot which makes the PSG go totally bananas.
For the Panasonic MSX2+ machines there might be a fix since you can read in which mode the machine is and multiply the pitch roughly by 5,37/3,57 (these figures probably have more decimals).
Actually this "feature" should've been emulated indeed.

By santiontanon

Paladin (787)

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11-04-2017, 02:59

hmm, if the frequency is multiplied by 1.5, that's going to be problematic, since dividing by 1.5 will be problematic (I was hoping it was just double, and I could solve it by just shifting the PSG values 1 bit to the right if Turbo was activated). But in any case, yeah, it'd be nice to have it emulated, to play around with a few ideas to see what works best Smile

By Manuel

Ascended (15441)

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05-05-2017, 21:56

In openMSX, all sound devices currently have their own individual clock, so the CPU clock is not affecting them.

By santiontanon

Paladin (787)

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06-05-2017, 01:34

Thanks Manuel! I saw your response in a separate thread about this as well Smile

By sd_snatcher

Prophet (3014)

sd_snatcher's picture

06-05-2017, 20:12

I said it there, and I'll say it here, so if someone googles for this topic in the future they can see the answer.

The PSG pitch change on some turbo machines is a hardware issue and must have a hardware fix. A software fix will always have the risk of undesired collateral effects (incorrect pitch, in this case) on unexpected cases. Here are some of them, but there might be others:

- The Sanyo MSX2+ machines feature the same switched I/O ports to command the turbo as the Panasonic MSX2+ machines. Even the bit that reports the turbo state is functional. The only difference is that the Sanyos don't have the turbo clock generator and consequently won't change the Z80 speed and PSG pitch.

- The Panasonic MSX2+ owner might be using a Padial SAN3 cartridge to fix the PSG pitch. Or any similar cartridge with its own PSG and its own fixed clock to feed it.

- The Panasonic MSX2+ might have a FB-Labs 10.74MHz biturbo kit installed. This kit also fixes the PSG pitch problem.