What Types of Cables are Susceptible to EMI?

[riverofwind]

Hi I have a quick question - what types of the below mentioned cables are susceptible to electromagnetic interference from being in close proximity to power cables in cable management setups? Does the EMI just interfere with the signal and therefore decrease its quality and max length? Does it have more of an impact on analog signals than digital signals? All the cables I could dream up include:

HDMI/Displayport
3.5mm mini jack audio cables
Speaker Wire
Ethernet (stp vs utp)
Phone
USB
Coaxial
Digital Coaxial
Digital Optical (obviously not)
Component Video and RCA/Composite kinda non-existent nowadays

Thanks!

 

[abacus]

Apart from optical all, however unless the cable is of poor quality (Screening is very poor) then the normal power cables will not be a problem.
Having said that, it is always good practice to cross power and low-level cables at 90deg to each other to reduce this problem.
Unless the equipment is poorly built, the only problem you could have is hum (If the cables are not up to the job), which can be cured by moving the power cable away from the low-level cable a few centimetres.

Bill

 

[riverofwind]

@abacus Thx good answer, what's a low-level cable though?

 

[12th Monkey]

Something carry a low voltage signal, such as your interconnects and (to a lesser extent) speaker cables.

 

[riverofwind]

@abacus @12th Monkey Thx guys... still have a couple questions.

What's an interconnect in laymen's terms? (Google failed me...) Is it just where any cable plugs in?

Also it sounds like quality digital signal cables with good shielding are negligibly affected by power cables and the only cables significantly affected are low-level cables, correct?

Do low-level cables also include 3.5 mm mini-jack speaker cables?

 

[abacus]

@abacus @12th Monkey Thx guys... still have a couple questions.

What's an interconnect in laymen's terms? (Google failed me...) Is it just where any cable plugs in?

Also it sounds like quality digital signal cables with good shielding are negligibly affected by power cables and the only cables significantly affected are low-level cables, correct?

Do low-level cables also include 3.5 mm mini-jack speaker cables?

Low level are the cables that connect your analogue equipment together, the most common having RCA phono plugs.

Bill

 

[riverofwind]

@abacus And non low-level digital cables are not significantly affected correct? Any chance you could explain why? Thx

 

[nopiano]

@abacus And non low-level digital cables are not significantly affected correct? Any chance you could explain why? Thx

It depends! Running, say, an Ethernet cable alongside mains wouldn’t be best practice, but it’s highly unlikely to prevent the data getting through. Your document will print, just as your streamer will play, you might say.

But, and it’s a big but, if you’re finessing a quality system, you might find slight differences in sound due to EMI (or eliminating it) which is what you asked about.

My experience suggests you don’t hear it in the signal, in the way that you’d hear hum in the analogue domain. But you might hear a sheen which disappears if you re-route the mains from the digital, or change the cables. Or an apparently lower noise - those blacker blacks you read about - with music standing out more clearly.

Big culprits for this type noise are ‘wall wart’ power supplies, Dect phones, Ethernet over mains devices, laptop chargers, etc.

With analogue signals, lower level signals are typically a volt or less, between a source and amplifier for example. Lowest of all is of course the unamplified signal from a pickup cartridge on its way to a preamp or phono stage. These are very delicate and highly susceptible to noise.

 

[riverofwind]

@nopiano Thanks, so sounds like EMI modifies the analog signal while it can negatively affect digital signals as well, but in a different way. Does it prevent data packets from successfully reaching the destination? Or does it modify the packets at all?

 

[nopiano]

@nopiano Thanks, so sounds like EMI modifies the analog signal while it can negatively affect digital signals as well, but in a different way. Does it prevent data packets from successfully reaching the destination? Or does it modify the packets at all?

Not that I’m aware of; that was my point about the music still arriving. You don’t get dropouts, and bits of music don’t go missing or change instruments! AFAIK it’s more about unwanted noise reaching components like DACs further along the digital chain. Have a read up as to why audio switches are recommended in a digital signal path - mainly to break the route for noise to follow the signal.

However, you seem to know an awful lot about the subject you asked about, so what are you actually trying to achieve?

 

[riverofwind]

@nopiano I understand most of the underlying concepts but don't have the knowledge to put the pieces of the jigsaw puzzle together. I am trying to achieve an understanding of everything.

It's totally clear to me now how EMI can affect audio cable signals, however one thing I'd like to confirm though is whether EMI from power cables onto digital cables like ethernet or HDMI has an affect at all. It is my current understanding that the shielding will eliminate some of the EMI but some can still make it through and subtly change the digital signal, possibly reducing signal integrity and thus signal strength and length of transmission. Is this correct?

 

[nopiano]

It is my current understanding that the shielding will eliminate some of the EMI but some can still make it through and subtly change the digital signal, possibly reducing signal integrity and thus signal strength and length of transmission. Is this correct?

Well, that’s not my understanding. As I said above it’s more about unwanted noise reaching components like DACs further along the digital chain, though the route of the connecting cables - like an Ethernet cable from your router to your streamer, say.

Taking each point you raise:-
1. You can’t subtly change a digital signal. It’s gets through or it doesn’t seems the best way to see it.
2. I don’t know what signal integrity is if the signal reaches the destination. See above.
3. Length isn’t relevant in a domestic setting, when USB and Ethernet reach tens of metres.

Try checking out ‘galvanic isolation’ for Ethernet. It’s more that unwanted noise affects other circuitry, perhaps including the analogue output from the DAC, than the digital signal per se. However, I’m straying beyond my comfort zone, so google can be your friend!

Lastly, these things can be very location dependent. So what works best for me, might not for you in the next town, let alone in another country.

 

[riverofwind]

@nopiano Would what I mentioned in the previous post apply if you are close to the length limit of whatever digital medium you are using, IE ethernet/HDMI/etc?

 

[nopiano]

@nopiano Would what I mentioned in the previous post apply if you are close to the length limit of whatever digital medium you are using, IE ethernet/HDMI/etc?

If you believe that the signal can’t be degraded then I don’t think so. But as I said previously, my experience is these things depend very much on the local environment. For example, my dealer in Bath (sadly now closed) was on an industrial park, and there was clearly engineering ‘hum’ nearby. As a result, I assume, they used a mains regenerator.

 

[riverofwind]

@nopiano So when you have EMI from power cables, it's inductive electromagnetic energy right? So you get constructive and destructive interference right? Any idea how a low-level EMI from a power cable wouldn't modify in meaningful way digital signals like ethernet/HDMI?

 

[nopiano]

@nopiano So when you have EMI from power cables, it's inductive electromagnetic energy right? So you get constructive and destructive interference right? Any idea how a low-level EMI from a power cable wouldn't modify in meaningful way digital signals like ethernet/HDMI?

I think we are getting a bit tied up in terminology now. I can’t answer this all.

You can experiment with your last question easily enough. Wrap mains and Ethernet together - what happens?

 

[riverofwind]

@nopiano Thx, I decided to post over at stackexchange to ask them for details, check it out

 

[Gray]

@nopiano Thx, I decided to post over at stackexchange to ask them for details, check it out

(...the preceding strangeness might just have been explained 🤔)

 

[riverofwind]

Me being strange? No question about that...

 

[nopiano]

@nopiano Thx, I decided to post over at stackexchange to ask them for details, check it out

It seems to me they say exactly what I said above, but in more understandable terms:-

“You can’t subtly change a digital signal. It’s gets through or it doesn’t seems the best way to see it.”

It also ignores the Hifi/audio issue of noise passing from source to DAC, regardless of the signal passing correctly. That’s what Hi-Fi brands spend time and money addressing.

However, it’s still far from clear why you are asking. Theory or practice? That’s a rhetorical question, by the way. I’m out.

 

[riverofwind]

@nopiano Theory and practice. I did appreciate your input for sure and that DAC noise situation is good to know. A couple things said over at stackexchange that weren't covered here:

Any disturbance happening on the wire will just slightly adjust the detection between logic thresholds and that may be seen as jitter and data transmission error.

and

every signal suffers at all lengths due to losses in transmission lines, digital signals start to have bit errors when length and disturbance affects the signal enough to be received incorrectly.

 

[riverofwind]

@nopiano I finally bought a Schiit Modi+ and hooked it up digital optical and usb power to my battery backup/ups. Do you think that the aforementioned signal noise passing along to DACs will affect me given my current power source not from a USB port? Also if I switched to digital coax would that be immune to EMI like digital optical or no? Thanks!

 

[nopiano]

@nopiano I finally bought a Schiit Modi+ and hooked it up digital optical and usb power to my battery backup/ups. Do you think that the aforementioned signal noise passing along to DACs will affect me given my current power source not from a USB port? Also if I switched to digital coax would that be immune to EMI like digital optical or no? Thanks!

I’m sorry but I have no idea, and have no experience with any Schiit products.

 

[Revolutions]

I guess you could call the Sex Pistols cables of a certain type.

 

[Al ears]

I guess you could call the Sex Pistols cables of a certain type.

What??