$4011 vs MMC5 $5011 for PCM streaming?

Discuss NSF files, FamiTracker, MML tools, or anything else related to NES music.

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frantik
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Re: $4011 vs MMC5 $5011 for PCM streaming?

Post by frantik » Fri Dec 11, 2020 3:30 pm

rainwarrior wrote:
Fri Dec 11, 2020 2:51 pm
If you want to make it 50% louder, you can send the same value to both (inverted on one).
For hardware output this might be worth exploring, anything to help raise volume away from the noise floor.
I think someone proposed a method of playing DPCM samples while playing PCM to do fine manipulations like that, which is a method that might play nicely with an IRQ approach. I can't find the thread for that one at the moment though.

Edit: I think this was the DPCM + PCM method I was thinking of:
http://forums.nesdev.com/viewtopic.php?f=2&t=20014
wow that is an even crazier idea than the one I had!

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za909
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Re: $4011 vs MMC5 $5011 for PCM streaming?

Post by za909 » Fri Dec 11, 2020 4:42 pm

rainwarrior wrote:
Fri Dec 11, 2020 2:51 pm
If you want to make it 50% louder, you can send the same value to both (inverted on one).

If you want to increase bit depth, if you could rely on MMC5 chips having a very consistent output volume (which you can't, but hypothetically if you could) I guess theoretically you could figure out a big table of all possible output levels and it'd have a few more bits of depth. "16-bit" is probably a massive stretch, I'd guess more like 9 or 10 at best. However, it's only hypothetical because this is actually impossible due to the inconsistency of both the 2A03 and MMC5 mixing.


However, if you want to produce extra bit fidelity, you could also jitter the values up and down in some sort of PWM/dither scheme, at the cost of a more dense output loop. (This is not an MMC5 specific idea, $4011 can do the same.)

I think someone proposed a method of playing DPCM samples while playing PCM to do fine manipulations like that, which is a method that might play nicely with an IRQ approach. I can't find the thread for that one at the moment though.

Edit: I think this was the DPCM + PCM method I was thinking of:
http://forums.nesdev.com/viewtopic.php?f=2&t=20014
Word of advice, I have since abandoned this idea, but it requires very precise timing in order to avoid producing the high-pitched artifacts in your sound that I was confronted with.

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Ben Boldt
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Re: $4011 vs MMC5 $5011 for PCM streaming?

Post by Ben Boldt » Sun Dec 13, 2020 2:07 pm

The MMC5's DAC, though it is 8-bit vs. the NES's 7-bit, is generally considered almost completely useless in practice. It would be a dream to find some sort of buffer functionality, at least big enough to get you from 1 Vblank to the next, but I looked and looked for that on the MMC5A and never came up with anything. Maybe some day it will be decapped and reveal something. There are still even a few unknown input pins. The mysteries are far from solved with the MMC5. Even the MMC6 is pretty mysterious in my opinion. There are at least 5 weird input pins on that one that I couldn't make any sense of.

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