It WORKS!

The lowpass filter DOES exist and it is enabled by default but the SMD cap is so small (250pF) that it has no effect on sound.
I soldered a 100nF cap for the quick test and it was too much and the sound was completely muffled from the right channel, but it proved my theory.
The SBPro mixer can disable it just like on a normal SBPro card, this works too.

Now the fun part begins, what Cap value will sound exactly the same as the SBPro?
Anyone familiar with the SBPro design especially the components of the lowpass filter part?
Can anyone tech/electronics savvy help me solve this mystery and make the YMF71x card the best card around for dos gaming.

I'll start by soldering some aligators or sockets so I can quickly switch the caps.

Friends I need a small recording of Doom with a CT1600 card.
Doom setup -> No Music.
Doom, idkfa, weapon 4, shoot straight ahead, just hold CTRL for a few seconds.

EDIT:
2.2nF, 4.7nF and 10nF sound pretty good.
Live recording of me connecting a 4.7nF cap on the fly to the sound card.
I can do accurate analysis of the frequency response to choose the perfect Cap value, but I need a CT1600 recording.

From what i can hear 4.7nF sounds too filtered. I guess that maybe its because i've been using YMF cards for the past 4 years and i've come to appreciate how they sound compared to a CT1600.

So if i do this to my cards i'll probably go with a 1nF value. That should be enough. But i'm interested in which value will give a closer result to a CT1600.

Great job on this!!

This sounds promising.

Here's the recording from my SB Pro. Switching DNFI on and off I got no difference that I can detect..

YMF71x Lowpass Filter FIX

Replace C11 and C19 (left and right) with 6.8nF capacitors, preferably 0805 (2012) 6.8nF SMD Capacitors.
This will make the YMF71x sound similar to the real SBPro which has a functional Lowpass filter, and now the YMF71x has too.
After many capacitors and frequency analysis I found that 6.8nF is the most accurate value and sounded closest to the CT1600 example firage provided, even closer than DOSBox.

So now along with the SB = 1 mixer fix and the modification it makes my Yamaha YMF719 the best DOS card I own.

Sound samples of various filters: HERE

Note: the PCB image shows yellow 4.7nF caps which later were changed to 6.8nF.

James-F wrote:

It WORKS!

Amazing! The lack of filtering has always been one of the things that bothered me about these cards so colour me interested in a mod to fix that 😎

Does the filter point shift when piping 44.1khz PCM via the WSS interface?

badmojo wrote:

Amazing! The lack of filtering has always been one of the things that bothered me about these cards so colour me interested in a mod to fix that 😎

The SB=1 fix and the filter cap mod makes the YMF a though card to beat.
No Single-Cycle DMA bugs (clicking and ringing), no MPU-401 bugs, no mixer bugs (now), no noise, and now a proper lowpass filter.
The only disadvantage is no ADPCM 2/3bit to 8bit support.

gdjacobs wrote:

Does the filter point shift when piping 44.1khz PCM via the WSS interface?

No, it affects only the SBPro emulation on the YMF71x.
The caps go to the SBFLTR pins on the chip, and have nothing to do with WSS.

Great job!

But you replaced 2 caps instead of just one?

I have to check my YMF-718 cards, i think i only own 1 YMF-719, but i guess it should be easy to find the caps on the 718's too. I will probably use SMD caps, just need to make sure i get the right size.

Once again, fab job!

carlostex wrote:

Great job!
But you replaced 2 caps instead of just one?

Thanks!
One for Left, one for Right.
The Audician 32 is IDENTICAL in every way, even the component names are the same.

Very nice! I think SMD caps are the way to go and would look very neat also.

James-F wrote:

gdjacobs wrote:

Does the filter point shift when piping 44.1khz PCM via the WSS interface?

No, it affects only the SBPro emulation on the YMF71x.
The caps go to the SBFLTR pins on the chip, and have nothing to do with WSS.

Interesting. What about SB Pro with 11khz samples? Does it filter at 5.5khz?

gdjacobs wrote:

Interesting. What about SB Pro with 11khz samples? Does it filter at 5.5khz?

No, it does not behave like the SB16 with a brickwall filter.
It behaves like the SBPro with a more mellow filter, you have a screenshot of a frequency analyzer above with 11khz samples form doom.

carlostex wrote:

I will probably use SMD caps,

PhilsComputerLab wrote:

Very nice! I think SMD caps are the way to go and would look very neat also.

Beware of SMD caps from ebay, they can be empty or the wrong value.
Make sure you have something to measure them.

Are we talking about those two mica ceramic capacitors (yellow)? I thought those were considered through hole caps, not SMD caps. You've soldered them to the surface since there are no vias there, so yes, they are mounted to the surface. But they are intended to be through hole caps, right?

clueless1 wrote:

they are mounted to the surface. But they are intended to be through hole caps, right?

Yes.
I used flux and made sure I don't cold solder them, should hold fine.

James-F wrote:

clueless1 wrote:

they are mounted to the surface. But they are intended to be through hole caps, right?

Yes.
I used flux and made sure I don't cold solder them, should hold fine.

I trust your soldering, I was just concerned about the terminology. 😀

That GODS piece is brutal. 🤣 First time hearing it. Good job.

firage wrote:

That GODS piece is brutal. 🤣 First time hearing it. Good job.

Yeah, James is a rock star with this thread. And the GODS theme sounds amazing in-game. Not that crazy about the game (or platformers in general) but I fire it up just to listen to the song.

Yea sounds great!

GODS is a slick game, but very hard. I think I only ever got to level 3 😀

Questions:

Does the SB 1.5 and 2 have a similar output filter?

Can someone link SMD resistors that are suitable for buying? I think I'm going to mod at least one of my cards.

EDIT: OT, but when I first heard the music, and I'm not a native speaker, I thought he was singing "The Two, The Waterfall". 😊