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Fascination with 80s arcade software synthesis

synth robotron defender jarvis sound

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#1 louisg OFFLINE  

louisg

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Posted Fri Jan 11, 2019 4:00 PM

I've recently become fascinated, again, with early software synthesis. For example, take Eugene Jarvis' sound engine in Robotron and Defender: I love that it ran on such a limited processor. But the thing that really gets me as a synth geek is the parameter space-- the fact that you can do so much with what I think he said was 8 parameters (in the Robotron GDC post-mortem). I see that he goes into a little more detail here: http://www.firepower...s_Interview.pdf-- it's funny too because we always think of general-purpose-CPU softsynths as a late 90s phenomenon! 

 

Now, I see someone has done a commented Robotron disassembly, but I don't think they got to the sound system. I'd love to find more info about it, short of disassembling it myself.

 

I also noticed that Konami's Time Pilot '84 produces a lot of similar tones. It supposedly uses one of those simple squarewave+noise PSGs, but it's driven by a reasonably fast CPU, which makes me wonder what's really going on there. Maybe it's manipulating the sound chip's registers really fast, or there's a bit-bang channel in addition to the sound chip. I think some of those dedicated PSGs had simple amplitude envelopes you could leverage, too..?

 

Any other arcade games that use or are suspected of using a softsynth to generate their sounds besides these and the Namco games? Any tones that strike you as particularly neat? 

 

I might play with some primitive softsynth concepts tonight. I want to see if I can make one that barely branches, and also see what FM does with such low resolution grainy tables (for example, do you really need a LFSR if you've got FM feedback?).


Edited by louisg, Fri Jan 11, 2019 4:01 PM.


#2 louisg OFFLINE  

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Posted Sat Jan 12, 2019 2:21 PM

So far, I'm finding that an 8-bit counter for frequency isn't enough at 22khz when indexing into a 64-byte waveform (so, 8-bit counter waveform position >> 3). I'm guessing these systems used 16-bit counters. FM feedback wasn't so hot with such simple waves-- some kind of rng is definitely needed for noise fx.


Edited by louisg, Sat Jan 12, 2019 2:21 PM.


#3 louisg OFFLINE  

louisg

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Posted Sat Jan 12, 2019 4:27 PM

I just found this! It looks like a pretty promising recreation of the sound routine: http://www.lomont.or.../Misc/Robotron/







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