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Crackling sound from PC to speakers via mixer

Started by GodAtum, Tue, 15 Sep 2020 19:19

GodAtum

I'm hoping some of our audio experts might be able to help.

I have an Intel NUC PC with a 3.5mm TRRS out. It doesn't have a have grounded mains plug (I am in the UK). This is connected to a Motu Stage B16 mixer via a TRRS to left/right split XLR cable. I then have a pair of active speakers connected via XLR to the mixer. The NUC is connected to a separate power strip to the mixer and speakers.

I have getting a very annoying clicking/static buzzing sound. But when I move my connection from the NUC to a proper desktop PC with a sound card it disappears.

Would a USB sound card or DI box (USB or jack one) solve my issue?

Hardy Heinlin

Is the NUC output too loud? Can you reduce the output volume of the NUC?

And is your 3.5 plug mono or stereo? If it's mono, the plug metal will make a short circuit on one of the two stereo outputs within the 3.5 jack. If this output is for headphones or speakers, the short circuit may hurt the electronics.

Jeroen Hoppenbrouwers

I found that the NUC series is supplied by the regular brick style small electronics adapter. This means it indeed isn't grounded at all. But you can still ground it! At the very least make sure that there is a firm connection between the audio cable shield and the truly grounded other end. It won't hurt extending the other grounded end through the shield to the NUC. Easily tried and likely to help a great deal.


Hoppie


GodAtum

Quote from: Jeroen Hoppenbrouwers on Tue, 15 Sep 2020 22:56
I found that the NUC series is supplied by the regular brick style small electronics adapter. This means it indeed isn't grounded at all. But you can still ground it! At the very least make sure that there is a firm connection between the audio cable shield and the truly grounded other end. It won't hurt extending the other grounded end through the shield to the NUC. Easily tried and likely to help a great deal.


Hoppie

I have tried a few cables including brand new ones. All the connection ends seem solid and secure. I am using these cables: https://www.thomann.de/gb/pro_snake_tpy_2060_kmm.htm

Not sure what you mean by extending the grounded end? Do I need some thing is static wrist band tied to it? Sorry I have no idea about electronics.

Hardy Heinlin

What do you mean by "clicking sound"? Is it kind of an overdrive clipping?* If so, I repeat my question:

Is the NUC output too loud? Can you reduce the output volume of the NUC?


* If not, is it a constant 50 Hz clicking noise?

GodAtum

This is a sample of the sound, I turned up the volume to be able to record it clearer. Nothing else was playing.

https://www.dropbox.com/s/c8qkt1mn2t8nrbf/sim%20sound.m4a?dl=0

I tried a USB sound card but that seems to make no difference.

Hardy Heinlin

OK, this sounds like a ground problem. *

It may be a ground loop. You said, your NUC isn't grounded. So a ground loop is actually unlikely. However, if the NUC is connected to a second or third device besides your audio device, that other device may generate a ground loop (if it's grounded). What devices are connected to your NUC? And are they grounded?


* How does it sound when your PNF is reading the checklist? Is the voice distorted or normal? If it's distorted, it's not necessarily a significant ground loop but just an extremely loud output volume which amplifies the humming background noise as well due to the extreme amplification. You get such problems when you connect the speaker output of device A with the mic input of device B, for example.

GodAtum

There's a lot of USBs connected to it like yoke and FDS parts.

here's it taxing on the ground: https://www.dropbox.com/s/aucviow64v6b4cr/sim%20sound%202.m4a?dl=0

It sounds distorted at points.

Hardy Heinlin

It's competely distorted. I can't hear any voice.

It sounds like Ringo Starr is playing Back Off Boogaloo while the steam engines of the Titanic are performing an Irish Dance.

GodAtum

Sorry that's just the engines and airframe sounds when taxiing. I have no PNF setup on this.

Hardy Heinlin

Anyway, the output is too loud, the input is too sensitive. Do you have any technical data?

GodAtum

Quote from: Hardy Heinlin on Thu, 17 Sep 2020 22:19
Anyway, the output is too loud, the input is too sensitive. Do you have any technical data?

What kind of data? I was putting the mic right next to the speaker to give a better recording. maybe recording it in a different way?

Hardy Heinlin

The data of your NUC's audio output: Impedance, voltage.

The data of your mixer's allowable input range: Impedance, voltage.

In short words: You shouldn't feed a mixer's mic input with signals from a speaker output.

Jeroen Hoppenbrouwers

Quote from: GodAtum on Tue, 15 Sep 2020 19:19
I have an Intel NUC PC with a 3.5mm TRRS out [...] connected to a Motu Stage B16 mixer via a TRRS to left/right split XLR cable.

XLR inputs sound a lot like sensitive balanced microphone inputs. Those most definitely are a very bad match for your simple 3.5 mm and likely ungrounded stereo headphone signals. It looks like that particular mixer only has microphone inputs; that isn't going to be nice. You want line inputs at the very least.

The alternative is a specialized cable that adjusts the impedance mismatch, but you may already have such a thing. It depends. If your current TRRS to XLR cable is just a cable, it won't be sufficient. There need to be some electronics in there, though they can fit in the XLR plug shell.

Also, is your mixer feeding phantom power into the TRSS? I hope not.


Hoppie

asboyd

Hoppie is spot on. The Motu Stage B16 mixer has microphone low impedance inputs. The level output of the NUC is at amplified/speaker level so it is saturating the Mic inputs, hence the distortion.

On a standard mixer there is normally a level (line impedance option) which allows switching between low and high impedance which introduces a -20dB pad (or on pro mixers a gain control pad)

Find out if your NUC output can be changed via the sound card driver (mixer) control.

You can get a High imp to balanced low impedance balun, that may help but I am not sure it would be compatible with the Motu Unit.

Regards,
AlexB
Alex Boyd... Sydney, Australia

garys

#15
Those Thomann 3.5mm to XLR cables that you linked too are TRS type not TRRS. That would mean that the ground part of the pin on the 3.5mm xlr cable is shorting out the ground/microphone pins of the nuc audio jack output. That would explain why when you move the cable over to a normal desktop pc sound card that has separate outputs for sound/microphone the problem goes away. I'm not versed in high end audio but that's where I think your noise is coming from.

Edit - I just tried something in my setup for a test to confirm what Hoppie and Alex were saying about the mic input impedance . I have a Mackie mix8 mixer that I use for PSX engine/airframe sounds.  I use the line inputs normally. I changed cables to use the mic xlr inputs. It instantly started clipping the mix 8 and output horrible distorted sounds similar to what you hear through the NUC.  I was able to correct it by tuning the output volumes on the Mackie.

Your stage 16 apparently has software DSP.  You should be able to change the output levels to such a level that they don't distort with the NUC.  Ultimately though you will want to look at a mixer with line level inputs and put the stage 16 to use for mawea and intercom duties.

asboyd

Being old school I use either a Yahama 16 analog channel mixer our my Soundcraft Spirit Live 16. These have both XLR (mic level) and 1/4" (line level) inputs. Each channel also has a gain control on the 1/4" input so I can adjust for anything which comes directly from a device at "amplified" levels (eg an electronic keyboard speaker output).
I also use DI boxes which change the levels from Line level to XLR Mic levels (some are analog, other I have made lately are digital)...

I would expect newer digital mixers would be software controlled and therefore should be able to be adjusted... otherwise they would not suit live variable situations.

Cheers,
AlexB
Alex Boyd... Sydney, Australia

GodAtum

Thanks all, somehow the PAD setting on the inputs was unchecked. Activating it did the trick!

garys

That's great to hear. Glad you got it sorted.

asboyd

Alex Boyd... Sydney, Australia