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Help improve the TIA sound emulation in Stella


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So, just like we (the Stella team) posted a thread about improving TIA graphics emulation, we now also want to start on TIA sound emulation. This work is documented at https://github.com/stella-emu/stella/issues/80.


Last year, some code was donated to Stella from crispy (Chris Brenner) from his FPGA work. At the time the TIA emulation core wasn't properly structured to make use of it, but now it is. As a result, Christian Speckner (DirtyHairy) has ported the code to Stellerator. The initial results are very good; many test ROMs that didn't sound quite correct are now properly emulated.


So now work begins on refining this code, and porting to Stella. What we need are test cases. That is, ROMs that illustrate where the current sound emulation is inaccurate/incorrect. We'd like you to test in Stellerator and in Stella 5, and (potentially) with new test builds of Stella as they become available. Please try to be as specific as possible when describing the issues (keeping in mind that it's hard to 'describe' sound). I'll start with some ROMs we already know about, in no particular order:

  • phaser06: correct in Stellerator, in Stella 5 the sound is 'idealized' and sounds much nicer than it should
  • tremolo: correct in Stellerator, left and right channels are properly 'mixed' and interfere with each other
  • E.T.: sounds much better in Stellerator
  • Ms. Pac-man: correct in Stellerator, there is now distortion from the analog mixing of left/right channels. In Stella 5 the sounds is 'better', but it is idealized and not like a real console.

Remember, just like when we were improving the TIA graphics emulation, the more test ROMs and cases we get, the better the results. So get testing :)

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I should add that it's been mentioned that some people may object to our improvements resulting in 'worse' sound. But remember that the goal is accurate emulation. If it sounds like crap on a real console, it should in Stella too :) To me, the actual sound is irrelevant; its accuracy compared to the real thing is all that matters.

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The post of a couple nights ago was based on my last use of my 2600 a couple years ago. Sadly, my current 'TV' (if you can call it that) doesn't have a coax input nor a composite jack, so no way to hook up my 6-switch Atari; nor do I have a Harmony cart, so no way to test the hundreds, maybe thousands, of software titles for audio abnormalities.


But for those reading this that have either the former or both the things I mentioned, this is a call for those betatesters to be: PLEASE. Send feedback on ANY findings of audio quirks to get the TIA emulation beefed up to make Turing blush!


Yes, I wrote those walls of text to say the little that needed to be said. I hope it helped. ;)

Edited by JFD62780
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Bumping this, since there hasn't been much response so far. I expected at least as much interest as when we were doing the TIA graphical improvements. Come on guys, please test and report any issues you find.


Interest is definitely there. Off the bat, ET was the big one for me. Honestly, I didn't realize the difference with Ms. Pac-Man until I performed a recent comparison.


It's just a matter of resource allocation right now. Graphic issues, I believe, are much quicker and easier to catch.


Sound related issues require more concentration and the ability to playback at reasonably loud enough levels to spot differences; sick fam (self included), and the upcoming holidays are not helping either. ;)


Phenomenal work being performed with Stella (and Stellerator), as always, and it is greatly appreciated. :)

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Yes, I understand that graphics are easier to spot issues. I'm also not a 'sound person', so I respond much better to visual rather than audio stimuli.


And it may be that there are simply less sound issues than there were video issues. Or more to the point, only a few ROMs illustrate the issue. ET and Ms. Pac-man are the worst offenders, and Thomas suggested a reason why that's the case. But we still need more test cases.


Sorry if the last response seemed pushy. I'm just irritated ATM since my main development system is down, and has been unstable for the past 3 months. So some of my irritation may have come across in the message :(

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Masters of the Universe: The Power of He-Man

(Title screen after the transformation sequence, theme melody)


Real HW (4-Switch Woody) = Distortion heard throughout parts of the melody (Similar to Ms. Pac-Man).

Stellerator = Extremely similar, if not exact match, to Real HW results.

Stella 5.0.2 = Sounds 'clean' throughout (Again, similar to Ms. Pac-Man).

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Frogger II - Threedeep!

(Short theme when pressing 'Reset')


Real HW (4-Switch Woody) = Slight dissonant ring at the end of each stanza/3 bars.
Stellerator = Matches Real HW.
Stella 5.0.2 = Each stanza ends clean, almost 'clipped' compared to the above.
Note: This is much more difficult to pick up on; however, it is definitely present. I thought it may have been a volume setting issue as Stellerator plays considerably louder at default than Stella maxed. However, cutting the PC volume in half and then a quarter for Stellerator playback, as well as experiencing similar with Real HW, there is the aforementioned dissonant ring heard that is missing with Stella's (5.0.2) playback.
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