No-cut SNES digital audio mod:

[FBX]

Pardon my ignorance, so you're putting an additional ADC and DAC (external of course) stage?

Tomorrow I'll be doing some research on how SNES audio works so I'll understand better what's going on.

Just an ADC that digitizes the S-Mix output, which will then be sent as 48Khz data to the CS8406 and output as digital coaxial. Another CS8406 will take the raw digital feed from the S-APU/DSP chip. A toggle switch will route which CS8406's output is active in the coaxial output.

[tjstogy]

If you're at that level of an audiophile that you'd solder in a replacement DAC for your SNES, what kind of audio setup do you have that doesn't include some kind of receiver or preamp? Am I missing something?

For anyone using powered speakers. Playing games on a pvm with a pair of powered speakers is easy- no need for switching inputs on a receiver every time you change what console you’re you’re playing. The scart switch goes right to the powered speakers. Turn the system on, and everything works. When you have a console that outputs coaxial audio only, not only is having a receiver necessary, but so is having to manually change the input on your receiver every time you are/aren’t playing snes (or any system that isn’t going through the scart switch). Not a huge deal, but an extra step. I don’t personally have a receiver for my retro console setup because it’s just extra stuff, and I prefer simplicity.

These are the speakers I use: Cerwin Vega XD4 Active Desktop Monitor Speakers https://www.amazon.com/dp/B00IJKMW4U/re ... yAbXX53ZTY

Having a “dac upgrade” available for older systems should also be beneficial for anyone using a good consumer grade tv, if the dac in the snes sucks as much as people have mentioned. People certainly don’t focus as much energy on audio fidelity as they do with video when it comes to the old consoles, and maybe dac upgrades for audio could be equated to RGB bypasses for video.

[Einzelherz]

If you're at that level of an audiophile that you'd solder in a replacement DAC for your SNES, what kind of audio setup do you have that doesn't include some kind of receiver or preamp? Am I missing something?

For anyone using powered speakers. Playing games on a pvm with a pair of powered speakers is easy- no need for switching inputs on a receiver every time you change what console you’re you’re playing. The scart switch goes right to the powered speakers. Turn the system on, and everything works. When you have a console that outputs coaxial audio only, not only is having a receiver necessary, but so is having to manually change the input on your receiver every time you are/aren’t playing snes (or any system that isn’t going through the scart switch). Not a huge deal, but an extra step. I don’t personally have a receiver for my retro console setup because it’s just extra stuff, and I prefer simplicity.

These are the speakers I use: Cerwin Vega XD4 Active Desktop Monitor Speakers https://www.amazon.com/dp/B00IJKMW4U/re ... yAbXX53ZTY

Would also be beneficial for anyone using a good consumer grade tv, if the dac in the snes sucks as much as people have mentioned.

I think what Bob means is that you're going to the effort to put an (arguably) better DAC in one console, either necessitating your other consoles getting a better DAC as well, or letting them stay noisy with analog. As opposed to pulling out the digital directly from each and just getting one proper DAC for them all.

And to answer Bob's quesiton - audiophilia can't be reasoned with, only spent money on.

[tjstogy]

I think what Bob means is that you're going to the effort to put an (arguably) better DAC in one console, either necessitating your other consoles getting a better DAC as well, or letting them stay noisy with analog. As opposed to pulling out the digital directly from each and just getting one proper DAC for them all.

And to answer Bob's quesiton - audiophilia can't be reasoned with, only spent money on.

That’s fine- except there are hardly any old consoles that you can mod for “digital audio”. I wouldn’t mind upgrading the DACs in all of my old consoles just as I (and lots of us) have rgb modded our consoles. If Borti says it’s possible to upgrade the old DACs, then I’m on board.

And videophilia is similar to audiophilia

Again- this is my opinion. Others have their own.

[darcagn]

I think what Bob means is that you're going to the effort to put an (arguably) better DAC in one console, either necessitating your other consoles getting a better DAC as well, or letting them stay noisy with analog. As opposed to pulling out the digital directly from each and just getting one proper DAC for them all.

And to answer Bob's quesiton - audiophilia can't be reasoned with, only spent money on.

That’s fine- except there are hardly any old consoles that you can mod for “digital audio”. I wouldn’t mind upgrading the DACs in all of my old consoles just as I (and lots of us) have rgb modded our consoles. If Borti says it’s possible to upgrade the old DACs, then I’m on board.

And videophilia is similar to audiophilia

Again- this is my opinion. Others have their own.

Pretty much any console in which you can replace the DAC (i.e. there's a standard digital signal on the mainboard that is compatible with a DAC chip you readily buy) you can convert the original digital signal to consumer S/PDIF digital audio. The only exception would be those with bizarre non-standard clock rates, which may be able to be safely resampled.

[FBX]

The only exception would be those with bizarre non-standard clock rates, which may be able to be safely resampled.

Speaking of which, the Super NES sample rate versus playback rate often gets confused in threads I read, in addition to the 'carved in stone' arbitrary sample rate somebody declared was 32,040Hz and that seemed to snowball as gospel. With the three SNES consoles I have, only the playback rate varied, while the sample rate stayed at a fixed 32Khz flat. I realized this when I recorded music tracks on two different consoles. The variance caused the music to be sped up or slowed down, not actually 'sampled' at that rate. Now what's really cool is the USB device I used to record the tracks didn't attempt to resample the incoming feed, and instead simply sped up the playback rate to 48Khz. When I set the playback rate to 32Khz, the music was now perfectly aligned in pitch with emulators. However, this was very slightly slower than the original speed in which it fed from the SNES. By comparing the length of an analog recording of the same music track on the same console, I was able to determine the playback rate native to each of my SNES consoles. One was playing at a rate of 32,055Hz, and another was playing back at 32,109Hz. Huge variance swing!


So the 32,040Hz 'gospel' is actually horseshit. Not only was it being confused with sample rate (which remains a constant 32Khz), it's also not going to be that value of playback rate for any given SNES console, unless purely by luck.

[xadox]

Great to see there will be some new solutions for the Audio Mod.
Because of the old "gluing technic" I only made the mod on one of my 1 Chippers.

[borti4938]

The only exception would be those with bizarre non-standard clock rates, which may be able to be safely resampled.

Resampling is not an easy task an requires some conversion steps. Other than with video material, where you try to retain the pixel sharpness and thus where you can simply copy samples, in audio material you can have to apply filtering in each step to avoid either spectrum copies in the spectrum (upsampling, filter after rate conversion) or aliasing (downsampling, fliter before rate conversion). Otherwise you will have will high frequency content and distortions.

Another problem takes place if you upsample the rate with a dedicated crystal like L-trains mod does. One might think 96kHz is 3x 32kHz but that's not true here as we don't have exact 32kHz and not exact 96kHz, here. This leads to a constant phase shift. I don't know how good is that handled by the rate conversion chip by TI there.
If you have equipment with plays the initial 32kHz by the SNES, you should prefere 32kHz instread of 96kHz!

Back to including MSU / SGB audio into the digital audio mod.

My personal idea would need to have a FPGA for signal processing as you need a) a PLL for rate conversion using the SNES SPU's clock and b) DSP / multiplier blocks for filtering.
If one samples the MSU data also with 32kHz, which may introduces a small loss here, a CPLD should be fair enough for combining SNES and sampled MSU streams.
Such an implementation can be safetely put as an addition to already installed audio mods. Unfortuanetely I don't have the time at the moment to realize that.

It's completely different here with FBX's approach. He comes from the analog world and applies ADC. This is the easiest way to combine the 32kHz and the 44.1kHz content. As he samples at 48kHz he does not break Nyquist sampling theorem related to the content. Nevertheless, I guess he will have a RC low pass designed for 48kHz (noise reduction by the DACs, Cartridge connector, etc.)

And here comes tjstogy's concerns about the quality of the SNES DAC. If you have a bad DAC before your second ADC in your processing chain - let's say the DAC is lossy - you will never be able to retain the lost information. The same applies if the S-MIX is faulty. And I've seen a lot of broken S-MIX ICs in the past.

FBX's approach relies on both: a good DAC and a good S-MIX.

Just a question to FBX:
You have written that you plan to multiplex the output of two outputs of two CS8406, right? Any plans for a second version to multiplex the PCM audio interfaces? This could be installed as an addition to already installed mods.

[FBX]

FBX's approach relies on both: a good DAC and a good S-MIX.

Yes, but it's for nostalgia purists, because all I'm doing is digitizing the analog feed of the SNES at 48Khz. So it doesn't matter what the quality of the DAC and S-Mix are. If they work and you like them, you'll be getting a relatively noise-free version of the analog feed in a single digital line, because it comes straight off the caps before it reaches the multi AV port. Apparently some people actually prefer the SNES DAC over straight digital (shocking to me, but they are out there), so this is right up their alley.

Just a question to FBX:
You have written that you plan to multiplex the output of two outputs of two CS8406, right? Any plans for a second version to multiplex the PCM audio interfaces? This could be installed as an addition to already installed mods.

PCM audio? Not quite understanding what source that is. My plans are to have a toggle switch, where one position feeds 48Khz 'S-Mix' digitized audio, and the other position feeds the 32Khz audio direct from the S-APU/DSP chip. It gives people the option of nostalgia and MSU-1 support versus pure 32Khz internal SNES feed. Where I am torn though is about what output type to use. Optical is more widely supported, but coaxial is easier to install with no cutting required. It's a tough call.

[borti4938]

I mean multiplexing two PCM streams (master clock, bit clock, left/right sync and data) from your two sources (your ADC and SNES SPU) to a single S/PDIF transmitter like the CS8406 on existing installs.

By the way: here is an blown S-MIX. Seems to become a common issue to what I feel.

[FBX]

I've seen those blown S-Mix chips before yeah, but if that's the case, you'd already know it because your multi-AV audio output would be screwed up too since it comes from that same chip.

As far as multiplexing the two PCM outputs, I just planned on using two CS8406 chips both in hardware mode. One handles S-Mix, the other handles S-APU/DSP, and a toggle switch handles switching the TXP output from them into the transmitting jack. That's the plan anyway.

[borti4938]

I've seen those blown S-Mix chips before yeah, but if that's the case, you'd already know it because your multi-AV audio output would be screwed up too since it comes from that same chip.

This can happen from one day to another And you will hear nothing anymore if this happens to your console. But I don't want to spread any fears; it's still very very unlikely that this happens.

If Borti says it’s possible to upgrade the old DACs, then I’m on board.

Possible:



Still, the S-MIX is between DAC and MultiOut, here.

[nmalinoski]

To capture digital audio from S-MIX games, it sounds like the game carts would need to be modified. Is there a clean way of implementing that--any unused pins on the 62-pin connector that you could hijack for S/PDIF?--or would you need to have an ugly coax dongle hanging off the cart that would connect to a socket on the console?

[FBX]

To capture digital audio from S-MIX games, it sounds like the game carts would need to be modified. Is there a clean way of implementing that--any unused pins on the 62-pin connector that you could hijack for S/PDIF?--or would you need to have an ugly coax dongle hanging off the cart that would connect to a socket on the console?

S-Mix is used by the SNES for every game. It's also where the cart analog left and right lines get mixed in with the internal audio, and that in turn gets sent to some caps and eventually the multi-out port on your SNES. So if you want digital cart audio from the MSU-1, you'd have to modify the SD2SNES by intercepting the feed to the DAC on the SD2SNES itself. Highjacking existing lines would be a risky idea because of all the things those lines potentially go through inside the SNES. Maybe you could convert the SD2SNES MSU-1 audio to transmission digital and then use the cart audio lines as digital feed, but you'd have to permanently modify the SNES console to never process those cart lines directly (i.e. trace cutting and intercepting before they run into any components on the board). Another downside is you'd lose Super Game Boy audio doing this mod.