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PostPosted: Sat Jan 06, 2018 10:58 am 
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I have finished my first "hot-plugging" program. It displays a white screen and beeps, expecting the user to exchange the RAM/Flash cartridge with an original Namco 163 Audio-equipped cartridge, then press A. It will play three 440 Hz tones: NES APU (gray screen), Namco 163 one channel (dark blue screen), Namco 163 eight channels (bright blue screen). I intend to acquire all ten of the games that use N163 Expansion Audio and record each one's output using the same hardware (Sharp Twin Famicom AN-505BK with clean audio mod; has nice APU vs. Expansion balance). That will provide a more precise measurement, using the exact same test tone rather than each game playing different music, of the relative volumes of the several games that use this expansion sound chip. This information then may help to update the Submapper proposal to reflect the relative expansion audio level of each game. Emulators can then let the user choose between original Famicom and GPM/AV Famicom APU vs. expansion sound levels.

The ROM has been successfully tested on real hardware, first by using an Everdrive N8 to upload the program to RAM, then exchanging the Everdrive with a Megami Tensei II cartridge and pressing A.
It sort-of works in most emulators, although most fail to honor the Sound Disable bit ($E000 bit 6), so they produce hanging notes when the screen goes black. Also, given the volume register value that I use, the one-channel and eight-channel test tone are just as loud; on emulators, the eight-channel tone is louder. Also on real hardware, the single-channel test tone sounds clean, while the eight-channel tone sounds "dirty", as expected.


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PostPosted: Sat Jan 06, 2018 4:37 pm 
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Thanks for doing this. I'll give it a try later, though I only have 2 N163 carts. I think ideally we want to try a lot of N163 carts on the same hardware, since the relative mix across games is the most important information here.

I've been thinking NSFe could accomodate an optional chunk for N163 volume, and 2A03 square vs. equivalent is an easy enough thing to standardize the mix values on. Plus we could have Famitracker export an NSFe with a value that represents "FT standard mix" for it and people might stop complaining to me that NSFPlay doesn't match their Famitracker expectations. ;)

(The other expansions don't seem to need it. 5B / VRC7 only had one game. FDS mixing wasn't part of the game. VRC6 had 3 games but I think they had a standardized mix, even though there's a lot of variance in the part tolerance.)


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PostPosted: Sat Jan 06, 2018 6:02 pm 
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I think I should expand the program to play both APU and Namco 163 at all fifteen volume levels. Right now, the APU plays at maximum amplitude while the Namco 163 plays at minimum amplitude, which might not provide sufficient information when taking into account the NES APU's nonlinear mixer.


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PostPosted: Sat Jan 06, 2018 6:26 pm 
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And here it is, all 15 volume levels for APU, N163 single channel, and N163 eight simultaneous channels. As before, the N163 waveform is one 32 sample/16 byte waveform consisting of 8 bytes $FF and 8 bytes $00.

When recording the output, it must be kept in mind that at the maximum volume, the N163 becomes much louder than the NES, up to eight times, depending on the particular mixing resistor on the game's circuit board.


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PostPosted: Sat Jan 06, 2018 6:38 pm 
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When you catalog the cart volumes, would you be willing to open and read, or measure the resistance across, the AUDIO FROM 2A03 and AUDIO TO MODULATOR pins ?

It really ought to be the case that the resistor there should be the only thing that determines the loudness of the mix, but what data we have is inconsistent.


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PostPosted: Sat Jan 06, 2018 6:42 pm 
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Is a simple $20 Ohmmeter sufficient for that task, or is something fancier required to do it correctly?


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PostPosted: Sat Jan 06, 2018 6:44 pm 
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A $20 ohmmeter is more than sufficient.


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