CMS/GameBlaster emulation thread

Emulation of old PCs, PC hardware, or PC peripherals.

CMS/GameBlaster emulation thread

Postby Jepael » 2017-1-08 @ 21:21

Thanks to NewRisingSun's DosBox patch to log CMS/GameBlaster audio into VGM files, there is now a way to get some source material for experimenting.

So I wrote a simple program that can read the DosBox-dumped VGM file and understand barely enough of it to render some GameBlaster audio output to a file.

At first try it was just outputting garbage, but after fixing one stupid bug, try to guess the look on my face when I first heard this!

The flac file is post-processed in Audacity, it is resampled from 3.58MHz to 44.1kHz and then high-pass filtered to remove DC offset.
So the renderer does not (yet) output audio file that could be played normally.

Let me know what you think.
I was kind of hoping it would sound somewhat better though, but what can you expect from square waves, no matter how great they are resampled/processed.

Also, this made me realize that VGM file can't properly handle external triggering of envelope generators, but fortunately this music does not use envelope generators at all.
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Re: CMS/GameBlaster emulation thread

Postby PhilsComputerLab » 2017-1-08 @ 22:53

I just listened to it and compared it with a recording of mine, it sounds great!

A bit quiet, maybe normalise / amplify before exporting. This is really easy with Audacity.

But yea, if DOSBox can sounds like this, that would be very awesome indeed :)

Thank you for helping.
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Re: CMS/GameBlaster emulation thread

Postby OPLx » 2017-1-09 @ 01:48

@Jepael: Here's the tool I wrote to play around with the SAA1099's registers (channels 0 through 2 only). You can use mouse and keyboard (space bar sets the values). DOSBox 0.74 has a bug with the mouse position in the 40x25 text mode so I would recommend using a different build. Hope this helps out with the emulation work. :happy:
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Re: CMS/GameBlaster emulation thread

Postby ripa » 2017-1-09 @ 20:39

I'd just like to say I listened to it and nice job.
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Re: CMS/GameBlaster emulation thread

Postby Jepael » 2017-1-21 @ 16:52

Any specific questions about how the real Philips SAA1099P chip works?
I've got a CT-1320 and some measuring equipment borrowed.

Here's how the PWM amplitude is applied to output tone for instance:
Reverse engineering
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