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PostPosted: Wed Jul 17, 2019 11:06 am 
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Perkka wrote:
I were also planning to not use the RCA outputs on the NES for sound but to have 2 of the on the expansion module, mainly because then i could reroute sound trough famicom cartridges the correct way which i guess would help with having sound levels the way it was intended. i guess it will make a difference at least.
That would require significant rework of the console. The two signals on the expansion port are "input to NES: mix audio in" and "output from NES: final mix" - there's no place for the Famicom's "amplified audio from 2A03" or "audio input to RF modulator" for a cartridge to stick its audio hardware in the middle.

If you compare the Famicom and NES schematic, "output from NES: final mix" is almost the same as "amplified audio from 2A03", but that's not useful without a place to re-inject audio afterwards.


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PostPosted: Wed Jul 17, 2019 12:48 pm 
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lidnariq wrote:
Perkka wrote:
I were also planning to not use the RCA outputs on the NES for sound but to have 2 of the on the expansion module, mainly because then i could reroute sound trough famicom cartridges the correct way which i guess would help with having sound levels the way it was intended. i guess it will make a difference at least.
That would require significant rework of the console. The two signals on the expansion port are "input to NES: mix audio in" and "output from NES: final mix" - there's no place for the Famicom's "amplified audio from 2A03" or "audio input to RF modulator" for a cartridge to stick its audio hardware in the middle.

If you compare the Famicom and NES schematic, "output from NES: final mix" is almost the same as "amplified audio from 2A03", but that's not useful without a place to re-inject audio afterwards.


Wouldnt that mean:
"output from nes: final mix" ->exp port reroute -> famicom cartridge -> exp port rca connector (possible with amp circuit) -> TV/Aplifier
be more or less like on a famicom?


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PostPosted: Wed Jul 17, 2019 1:07 pm 
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Er. Yes.

How are you handling carts that haven't been modified for this, though?


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PostPosted: Wed Jul 17, 2019 1:20 pm 
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lidnariq wrote:
Er. Yes.

How are you handling carts that haven't been modified for this, though?


Possibly a switch that i can use when playing famicom games and when im not.

so ill be able to switch between
"output from nes: final mix" -> exp port reroute -> famicom cartridge -> exp port rca connector (possible with amp circuit) -> TV/Aplifier
and
"output from nes: final mix" -> exp port rca connector (possible with amp circuit) -> TV/Aplifier

Dunno if i could make something sense if the famicom adapter is connected and then have a relay switch between the two routes.


Because wouldn't this way of outputting famicom sound be more correct then the 47ohm resistor mod most people do?


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PostPosted: Wed Jul 17, 2019 1:54 pm 
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Perkka wrote:
Wouldn't this way of outputting famicom sound be more correct then the 47ohm resistor mod most people do?
47 kiloohm.

But meh? It doesn't really matter how the audio is mixed as long as the balance is close enough to correct: you're unlikely to hear a difference between a properly set mixing resistor and recapitulating the Famicom's audio pathway. There's only one exception I can think of – it seems that one game that uses Namco's 163 puts a lowpass filter in the cartridge. This filter would also affect the 2A03's audio in a Famicom, but would only affect the 163's sound in a modified NES. But this pedantic increase in accuracy would sound muddier: subjectively worse.

Speaking of recapitulating the Famicom's audio pathway, the original Famicom is RF-only, and RF-modulated TV audio has so-called "75µs preemphasis", which requires deemphasis hardware (a lowpass filter at 2kHz) inside the TV. I believe I don't see anything to add this preemphasis inside reverse-engineered schematics of the RF modulator, so audio via an RF stage will be muddier than audio via the front-loader's RCA output.


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PostPosted: Wed Jul 17, 2019 1:59 pm 
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lidnariq wrote:
Perkka wrote:
Wouldn't this way of outputting famicom sound be more correct then the 47ohm resistor mod most people do?
47 kiloohm.

But meh? It doesn't really matter how the audio is mixed as long as the balance is close enough to correct: you're unlikely to hear a difference between a properly set mixing resistor and recapitulating the Famicom's audio pathway. There's only one exception I can think of – it seems that one game that uses Namco's 163 puts a lowpass filter in the cartridge. This filter would also affect the 2A03's audio in a Famicom, but would only affect the 163's sound in a modified NES. But this pedantic increase in accuracy would sound muddier: subjectively worse.

Speaking of recapitulating the Famicom's audio pathway, the original Famicom is RF-only, and RF-modulated TV audio has so-called "75µs preemphasis", which requires deemphasis hardware (a lowpass filter at 2kHz) inside the TV. I believe I don't see anything to add this preemphasis inside reverse-engineered schematics of the RF modulator, so audio via an RF stage will be muddier than audio via the front-loader's RCA output.



Ok, i thought there was more issues with the mixing and different volumes, but maybe that was only faulted by the everdrive being bad at reproducing it and not an issue with real carts?
Just know there is some people adding a potentiometer instead so they can tune the volume per game basis because of different volumes, and i thought that was because of the way it was mixed was not as its intended.


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PostPosted: Wed Jul 17, 2019 2:26 pm 
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Well, expansion audio via modded NES needs a configurable volume. Period. Otherwise there will be mismatched mix levels. (Edit: Mismatched when using different cartridges, I mean.)

The 47k fixed resistor was an idea from years ago, at a time when we had a lot less information than we do now about expansion audio. (A maybe naive assumption that the problem could be dealt with at the mapper implementation level... which did not work out, in the end.)

Everdrive and HD-NES both have software level adjustments at this point. PowerPak doesn't have one, but it hasn't been revised/updated in about a decade. In the absence of a software control, you can install a pot instead of a fixed resistor. Solves the same problem, just at a different point in the chain.


If you're building new hardware to support your new mapper idea, for the most widely compatible results I guess you want to build a device that will have the proper mix when a 47k resistor is applied.


Last edited by rainwarrior on Wed Jul 17, 2019 11:03 pm, edited 1 time in total.

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PostPosted: Wed Jul 17, 2019 8:06 pm 
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rainwarrior wrote:
Well, expansion audio via modded NES needs a configurable volume. Period. Otherwise there will be mismatched mix levels.
But that's the entire point of his idea. Recapitulate the mix circuit at the point where they differ (namely: in the original Famicom, cartridge pin 45 is almost identical to the original NES's expansion port pin 22), and export it out the bottom instead of trying to re-inject it.

Or if the NES's use of a 74HCU04 produces too much of a volume difference relative to the 40H368 in the Famicom, maybe instead tap NES expansion port pin 3 instead and rebuild the 40H368-based amplifier instead.

Then again, we already have the problem that the first- and second- party Famicom models from the original runs have different mix levels anyway, so maybe this is still doomed. But I don't have enough domain knowledge to say.


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PostPosted: Thu Jul 18, 2019 9:46 am 
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lidnariq wrote:
rainwarrior wrote:
Well, expansion audio via modded NES needs a configurable volume. Period. Otherwise there will be mismatched mix levels.
But that's the entire point of his idea. Recapitulate the mix circuit at the point where they differ (namely: in the original Famicom, cartridge pin 45 is almost identical to the original NES's expansion port pin 22), and export it out the bottom instead of trying to re-inject it.

Or if the NES's use of a 74HCU04 produces too much of a volume difference relative to the 40H368 in the Famicom, maybe instead tap NES expansion port pin 3 instead and rebuild the 40H368-based amplifier instead.

Then again, we already have the problem that the first- and second- party Famicom models from the original runs have different mix levels anyway, so maybe this is still doomed. But I don't have enough domain knowledge to say.


Exactly :)
because i believe the first Famicom at least should have correct volume matching, would be quite sad if it didn't.
I have another issue and that is creating a working expo port connector, but that's a whole different story :P

I believe this project with all parts involved will take quite a long time :) (not to talk about my other NES projects)


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