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About SD Card access noise

08 Oct 2019, 22:11

Hi folks !

I think many people have to deal with the problem of buzzing sound during SDcard access on SSDS3. I purchased my SSDS3 revB early this year for my Coregrafx 1, using a micro SDXC Sandisk Extreme 64Go. And I was confronted with this issue like many over people. Well, honestly, the problem is not so noticeable when music is playing and I still enjoying my new SSDS3.

This week, I decided to upgrade my 64Go microSD card with a 128Go model. I choose a SDXC Transcend 300S, essencially because of a deal on Amazon. Well it was the REAL DEAL because SD card access noice has almost disappeared with this card ! At normal sound level, it's even inexistant. I make a short video to show this. My installation is not audiophile and I put the sound to max on my little stereo system, so there is a lot of analogic noise, but the difference about SDcard access noise is flagrant.

I hope this could help people this this problem :)

Last edited by Zenkuro on 10 Oct 2019, 20:11, edited 2 times in total.

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Joined: 26 Jun 2019, 15:15

Re: About SD Card access noise

09 Oct 2019, 01:23

Cool - so you reckon to stay away from sandisk cards?

I'd be lying if I said I wasnt concerned about this when I buy an SSDS3

I thought FBX had tested different SD card types and it hadnt made a difference?

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Re: About SD Card access noise

09 Oct 2019, 01:41

Hmmm that’s interesting.
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Re: About SD Card access noise

09 Oct 2019, 13:27

Well I tested with 2 more microSDXC card :
- SanDisk Ultra 128Go : bought on 2017 for my Switch, same problem of buzzing than SanDisk Extreme 64Go previously used.
- Lexar 633x 256 Go : bought this week for change the SanDisk Ultra on my Switch. And as the Transcend 300S, no more buzzing !

So I don't know exactly why , but yeah, the microSD model make the difference ! It will be interesting than everyone give is microSD model to check if there is an access noise or not with it.

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Re: About SD Card access noise

09 Oct 2019, 15:02

Awesome news!

I know which SD card I'll be buying!

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Re: About SD Card access noise

09 Oct 2019, 16:27

Did some tests with SSDS3 revision 2.

Tried with Sandisk, Toshiba, Kingston and Samsung cards. There is additional noise when accessing the SD card. Clearly notable if the sound volume is very high and no background music is playing. It disappears as soon as the green LED stops blinking. Like in the video above.

Last test was with a low end 2GB Transcend card. And indeed, no additional noise when the green LED is blinking!

Great finding. Thanks. 8-)

Wondering if there's a technical explanation from neodev.

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Re: About SD Card access noise

13 Oct 2019, 05:10

If I had to hazard a (absolutely blind) guess, the SD cards are putting noise on the 3.3V rail, which is then being picked up on something in the audio path. I would want to spend some time probing the audio path with a decent oscilloscope to see where the problem originates from, now that you have a way to reliably show the problem.

It may end up being that certain SD cards are fantastic at conducting EMI out of the power rail, so an additional C-L-C pi filter to the SDcard power rail should fix that (if it was the case). This is, of course, assuming that the audio path IC's have proper decoupling.

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Re: About SD Card access noise

13 Oct 2019, 09:51

gwdoiron wrote:
13 Oct 2019, 05:10
This is, of course, assuming that the audio path IC's have proper decoupling.
The SD access noise doesn't come from the audio path, but rather permeates the console and then affects the audio. This is why larger consoles like the Super Grafx and TG-16 have considerably reduced SD access noise, because they have much bigger ground planes to sink that noise into. I recall on the MegaSD work I did, I was able to prove this concept by completely removing the entire audio circuit such that the audio pins were completely isolated, and the SD access noise was still just as loud, even though no audio was being sent into the Genesis (and not even connected).

At any rate, that is very interesting about Sandisk cards being really bad about this. I'll snag one of those other cards and have a listen myself. But it sounds like a special recommendation should be made on what cards to use after we confirm this.

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Re: About SD Card access noise

13 Oct 2019, 10:51

Yes, I think the problem is related to the power usage of the card, and not a radiated noise. When the card starts reading, there is probably a higher power usage spike, the ssds3 regulators will try to draw more power from the internal console regulator, and if it's not fast reacting, there will be a small dip in the voltage level in the internal console power lines till it reacts. That will probably affect the amplifiers in the audio circuit, or anything that is referenced to that voltage line, causing some alteration of the amplitude, and being heard as a buzzing noise, and it's generally happening at a constant 75Hz frequency (the 1x CD read speed is 75 sectors per second) and it's audible.

The SD card interface in SSDS3 has capacitors to try to avoid these spikes, by providing the neccesary peak current, but they can only react to peaks, if it's sustained, they will eventually let that increased draw pass to the regulators and to the internal console power circuit (yes, we tried with larger, smaller, different combined values, and it didn't affect noise at all).

Probably some SD cards are more power efficient, or have less peak current usage, or maybe the increased power draw has a slower ramp that allows the internal console regulator to compensate that increased current requirement, and doesn't cause the power noise.

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Re: About SD Card access noise

13 Oct 2019, 16:24

It could be that Sandisk is more aggressive on power savings when in standby (making the transition to "in use" so much more of a transition).

It's not easy to reduce this without applying a bunch of math to it to reduce specific frequencies; you can add capacitors adjacent to the power-consuming unit (as they have), you can add them in a "decade" pattern (10uF, 1uF, 0.1uF, etc.), you can do the same at several points along the power transmission pathway, particularly at the input and output of the regulators (as I'm sure they have), and some people also use inductors (which I wish I knew more about).

For something like this, it might be strong enough that a specific design is required in order to eliminate it. I'm sure that it wasn't anticipated during development, especially as some cards act differently than others.

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