• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Dealing with EM noise

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
I made the purchase by the Surge energy rate as the primary purpose I expected is to protect the connected devices, and values above 2000Joules were recommended to me by an electrical engineer.

That it will do. When there is a line filter in there (common mode rejection of 60dB says there is) means it will filter common mode currents above a certain frequency. It will probably reach -60dB between 100kHz and 10MHz or so.
It will filter absolutely nothing within the audible range... well maybe a few dB tops (common mode not differential mode) at 20kHz or so.

What you suspect is a surge is what is called 'inrush current' and is cause by the smoothing caps in the SMPS on the mains side being charged in the first few cycles of the main frequency.
They are current surges of course but the surge filter inside will only limit (clip) voltage surges on the mains.
The impedance of the common mode choke being used will somewhat limit the mains currents through the power strip.
 

zermak

Senior Member
Joined
Jun 2, 2019
Messages
372
Likes
251
Location
Italy
There is a difference between USB frequency and mouse polling rate.

In short, mouse sends data up to set polling rate. Since it high-priority ISR call, its better not to send data all the time, but only when there is an update.
That's what I wrote, if you move the cursor/mouse.

I trashed/put in a drawer my Khadas Tone Board because it picks up the 1000Hz polling rate and even if it is inaudible it bothers me. I am back on my on board audio: less cables and boxes around.
 
OP
O

Offler

Senior Member
Joined
May 27, 2021
Messages
414
Likes
399
That's what I wrote, if you move the cursor/mouse.

I trashed/put in a drawer my Khadas Tone Board because it picks up the 1000Hz polling rate and even if it is inaudible it bothers me. I am back on my on board audio: less cables and boxes around.
Sorry I missed that.

I recommend to adjust polling rate according refresh rate of your display. Like 60Hz display will be fine with 125Hz polling rate, 120Hz with 250Hz and so on.


Just went through datasheet for my PSU. Its designed for 100-240v@13-6,5A (1300-1560 watts), which are absolute maximum values and are probably achieved only when PC is powered on. Original cable might limit that a bit to 6A, which is a rating of a 0,75mm wire.
 
Last edited:

zermak

Senior Member
Joined
Jun 2, 2019
Messages
372
Likes
251
Location
Italy
Sorry I missed that.

I recommend to adjust polling rate according refresh rate of your display. Like 60Hz display will be fine with 125Hz polling rate, 120Hz with 250Hz and so on.
Why? It doesn't make sense. The higher polling rate is for receiving/sending higher number of packets and it is useful for mouse movements' data (do you know the blurbuster.com site and its articles/analysis?). Plus the PSU in the PC and the monitor are not related.
And well for example with Freesynch/G-Sync monitor and the feature enable the monitor's frequency is costantly changing based on your in game framerate if your graphic card can't mantain a constant framerate equal to your monitor set frequency :)
By the way I am using a 144Hz monitor now, with Freesync capabilities but I don't use it becasue of input lag and other reasons.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
Just went through datasheet for my PSU. Its designed for 100-240v@13-6,5A (1300-1560 watts), which are absolute maximum values and are probably achieved only when PC is powered on. Original cable might limit that a bit to 6A, which is a rating of a 0,75mm wire.

PC power supplies are wide range and the current is voltage dependent so a little sag during inrush currents is no problem.
When the mains cord gets warm during usage this might show a problem.
Peak currents can easily exceed 50A yet stay well below 6A on average.
 
OP
O

Offler

Senior Member
Joined
May 27, 2021
Messages
414
Likes
399
Why? It doesn't make sense. The higher polling rate is for receiving/sending higher number of packets and it is useful for mouse movements' data (do you know the blurbuster.com site and its articles/analysis?). Plus the PSU in the PC and the monitor are not related.
And well for example with Freesynch/G-Sync monitor and the feature enable the monitor's frequency is costantly changing based on your in game framerate if your graphic card can't mantain a constant framerate equal to your monitor set frequency :)
By the way I am using a 144Hz monitor now, with Freesync capabilities but I don't use it becasue of input lag and other reasons.

Blurbusters sell some of snakeoil in the PC gaming segment.

For example they mix together Display Refresh Rate with Pixel GTG time claiming that Refresh rate is responsible for "ghosting" effects. If you get good 60Hz display with real 1ms GTG, you will have nice and sharp image. Their UFO test is obviously fake, because it relies on human perception, and if you take that test apart, you will see its fake.

What BBs did right was to raise awareness between GtG and MPRT. Thats actually helpful.

When it comes to mouse polling rate, there is always a limiting factor - your display is the last one in the chain.

For example if you play old 3d game which runs on 300FPS, yes it makes sense to use 500 or 1000Hz polling rate, regardless your display has 60 or 120Hz refresh rate. Effectively you will see only as much frames as is refresh rate of the display.

But if you run 3d game at 60FPS, 125Hz polling rate is adequate. Lowering polling rate from 1000Hz might be beneficial to Core0 and actually getting few more FPS.

If there is significantly higher polling rate than FPS or refresh rate, buffers will overflow, CPU will have to process more data which will not be used in the end frame and input lag will actually get worse.
 
OP
O

Offler

Senior Member
Joined
May 27, 2021
Messages
414
Likes
399
PC power supplies are wide range and the current is voltage dependent so a little sag during inrush currents is no problem.
When the mains cord gets warm during usage this might show a problem.
Peak currents can easily exceed 50A yet stay well below 6A on average.
So I did combined hearing + measuring test.

First i calibrated the amplifier volume and measuring levels at -65dB.
test111.jpg


Then I decreased volume of the generated sinewave to -95db where i could safely say I could not hear anything.
test112.jpg


As you can see, noise level is below 95dB and taking 1KHz sinewave is absolutely inaudible to me, i can safely say that noise is inaudible as well.

Then i maxed out the amplifier.
test110.jpg

Sinewave got back to -65dB, and the sine sound is audible again so I can assume the amplifier increased signals by roughly 30dB.
Noise floor flattened and raised to about -120dB.
New spikes showed at 2.2Khz, and some at 15KHz and 16KHz where are my hearing capabilities quite poor.

But most importantly, the noise spikes below 1KHz did not raised at all, not by 30dB as the 1KHz signal. Harmonic spikes are now below noise level, or did not raised by 30dB. 2KHz is still at -120dB, 3KHz at -117.5dB, 5Khz at -115dB.

That simply means that this noise is NOT being amplified and its not present in the speakers.

As a side effect I measured and calculated that my amplifier has THD (without N) of -89dB and SNR of 90 at max, and THD -95dB and SNR 99dB at volume sweetspot.
 

AnalogSteph

Major Contributor
Joined
Nov 6, 2018
Messages
3,338
Likes
3,278
Location
.de
OP, I think your measurement setup inadvertantly includes a ground loop... more like two, in both directions (the D3020 v2 seems to be a Class I device). There is no way to get clean results with the equipment you have right now (though I guess the obvious difference in PE resistance between mains leads is good to know). At the very least, a balanced input would be very much recommended... typically this means a $150-ish audio interface. (*) A matching balanced attenuator for speaker to either input line or mic level (depending on which one performs better and what levels it'll handle... check Julian Krause's reviews) is recommended as well.

You are not the first to attempt such measurements either, check e.g. this thread.

*) I mean, if you are really, really cheap, a stereo unbalanced input can serve as a mono balanced input in a pinch. The only problem is that you have to invert one channel and add it to the other one, which is simple enough in an audio editor but may prove infeasible live... I don't think REW can analyze an offline recording like RMAA will do.
 
OP
O

Offler

Senior Member
Joined
May 27, 2021
Messages
414
Likes
399
OP, I think your measurement setup inadvertantly includes a ground loop... more like two, in both directions (the D3020 v2 seems to be a Class I device). There is no way to get clean results with the equipment you have right now (though I guess the obvious difference in PE resistance between mains leads is good to know). At the very least, a balanced input would be very much recommended... typically this means a $150-ish audio interface. (*) A matching balanced attenuator for speaker to either input line or mic level (depending on which one performs better and what levels it'll handle... check Julian Krause's reviews) is recommended as well.

You are not the first to attempt such measurements either, check e.g. this thread.

*) I mean, if you are really, really cheap, a stereo unbalanced input can serve as a mono balanced input in a pinch. The only problem is that you have to invert one channel and add it to the other one, which is simple enough in an audio editor but may prove infeasible live... I don't think REW can analyze an offline recording like RMAA will do.

NAD d3020 v2 is Class D amplifier, NAD modified Hypex UcD102, with integrated DAC Cirrus Logic CS42528 (24bit ,192Hz is plenty for me), and PSU is modified Hypex SMPS400A100. I wanted something with low power consumption.

1. Really reallly reaally cheap.
I have some technical background in IT and software, but i am not that good with electronics. I just wanted to make sure that i am not being sold snake-oil.

2. I planned to borrow USB DAC/ADC, isolated from the PC.
That way I could get much better measurements, lower noise floor, less spikes.

3. NAD d3020 v2 has Optical SPDIF input
That means I can feed the data to it over electrically isolated line, isolating any noise coming from PC.

That is however not true for the Line-In I used for measuring.


This is the software I use:
https://www.audiotester.de

Which means:
a) As an input for measurement is used LineIn in computer soundcard, and its clearly very noisy input.
b) As an output for measurement i used headphones jack on NAD d3020v2, not speaker output.
At this point i was accounting for really big margin of error, but the results are much better I expected.

c) I confirmed SNR and THD values provided by amp manufacturer to be true and I could compare the measurements with reviews on this forum.
d) I found volume sweetspot were THD goes much lower (-80dB as manufacturer says, i measured as low as -95dB THD)
e) I confirmed that audible coilwhine from GPU under stress is audible through speakers if used Analog AUX input, but its isolated if using Optical SPDIF.
f) I confirmed that Windows distorts sound if its above certain volume level (CAudioLimiter issue).


4. The software measures noise in audible spectrum, and some of it was picked by the wire for the loop
While I was trying to figure out the source i found busted power cord, which was causing issues in PC itself, but earlier today I confirmed that measured noise is not audible, which basically makes it a different kind of issue, not for this forum. I took it as a hint to replaced older power strip with newer power surge and I plan to replace some of the inadequate power cords.

So I managed to perform certain tweaks without much investment on testing equipment...
 
OP
O

Offler

Senior Member
Joined
May 27, 2021
Messages
414
Likes
399
So the issue has been partially explained on a different tech forum. I wasnt looking for audio quality, but rare SW issue.

Seasonic Prime Ultra Titanium 850W model has a flaw which allows noise generated in the Graphic Card of a computer to pass through the unit to the 24pin connector, +12v sensing on the mainboard.

If the GPU was specifically Nvidia 3090, the noise would kill the system and cause power cycle issue (system would reboot indefinitely).

I dont have this graphic card, but i definitely measured noise generated by the GPU coils out of audio and USB connectors - so called "coil whine" as it can be in audible band. What concerns me more is noise above audible band.

Seasonic recommended to use ferrite core on the cable, or they delivered new cable which is not using the affected power line. I will take a look for some ferrite chokes and try them out.
 
Top Bottom