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 Post subject: VRC6 Accuracy Comparison
PostPosted: Tue Dec 19, 2017 9:26 pm 
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So I recently picked up a Sharp Twin Famicom while I was in glorious Nippon as well as a bunch of games, one of which being the J version of Castlevania 3. I've been comparing with Nestopia for accuracy to determine the difference (if one exists) between emulation of VRC6 and hardware use of it and have done the following:

- Tested on the same TV with the same volume levels
- Emulation is being done on a PC with HDMI
- Famicom is outputting composite with a legit cart, no flash cart business
- Using the regular version of Nestopia, no Retroarch or whatnot involved

Now my findings are as follows:

- Nestopia seems to play VRC6 loudly compared to hardware

- In Nestopia, the "umph" or more bassy noises seem to be much more subtle to the point that they almost seem missing. It's like someone turned the dial all the way to treble

Now here is the question.. What difference if any does this really make for one? For all intents and purposes, both sound great, but I'm honestly just curious at this point for science, so whatever. The main question is whether or not my testing is truly valid? I do have a CRT and a PC with a video card in which I can do composite and such to replicate the cable if I should do that, but is composite really that bad if that is the source of the difference? At that point it's almost up to debate what the "intended" experience is regarding the chip. Obviously they expected audiences to have composite at *best* at the time, but perhaps the machines they developed on sounded far better? This is really all up to speculation, just a topic I find interesting.

Anyways, if you actually read up to here, cool and thanks.


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PostPosted: Tue Dec 19, 2017 9:51 pm 
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If the Twin Famicom's RF output stage is anything like that of my NES, it noticeably boosts the bass and cuts the treble compared to composite. Do you have an EverDrive or other means of running cart homebrew on the Twin? If so, I've made an equalization test ROM that can generate a sine sweep and pink noise test signals.


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PostPosted: Tue Dec 19, 2017 9:58 pm 
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tepples wrote:
If the Twin Famicom's RF output stage is anything like that of my NES, it noticeably boosts the bass and cuts the treble compared to composite. Do you have an EverDrive or other means of running cart homebrew on the Twin? If so, I've made an equalization test ROM that can generate a sine sweep and pink noise test signals.


I do have an everdrive N8, but it uses a US board and thus needs an adapter to work which I do not have. On top of that, I was not using RF, which I feel like is at least of note here.


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PostPosted: Tue Dec 19, 2017 11:42 pm 
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A friend of mine owns two copies of Akumajou Densetsu, and unfortunately they had very different mix levels when we tested them, and myself I have an Esper Dream 2 cart and it was at yet another level.

So... I wouldn't say your tests are entirely invalid, exactly, but looking at one cart even with differing hardware isn't very conclusive. Maybe a survey of multiple carts each with multiple hardware could start to work on a better average, but all the variation I have seen in tests is unfortunately a big problem.

Though I would say that "emulator so-and-so seems louder than my cart" is not yet a useful data point. If you could take a recording and actually measure the volume of the VRC6 relative to the 2A03 channels we can put quantifiable numbers on it. Even without being able to test the same cart on multiple hardwares or vice versa, having one more data point is better than not having it.

I had written some hotswap test ROMs for this a while ago and collected some data from recordings for NSFPlay's default mixer settings, but I have misplaced this stuff. I would like to do another survey of this in the future and remember to document it better and make it public. (I think for testing purposes, the differences between CRT/RF/etc. don't really matter much, if you can play the same waveform at the same frequency on both halves of the 2A03 and your expansion cart, it should be valid to compare their relative volume in most cases).


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