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Use of ferrite beads on usb cables
Old 1 week ago
  #1
Here for the gear
Use of ferrite beads on usb cables

Hello,

I just started looking into reducing the ground loop hum in my studio setup and came across those ferrite beads thingy you clip on your cables. I have a couple of question regarding these.

First, I did a comparison test hooking my audio interface to my computer with a usb cable fitted with a ferrite bed and it definitely reduced the hum compared to one without. Now I'm thinking about buying a bunch of those beads (cheap enough) and fit them on all of my other usb cables, but I'm wondering if there is any point, because all the other usb cables are only used to transmit MIDI to my synths, not audio. So would those ferrite beads improve the situation still?

Secondly, would it not be better to have ferrite beads fitted on my interface-to-speaker monitors cables instead? The amount of parasite noise on my recordings is relatively low already, enough to be acceptable (I already use Behringer hum removers that do a good job), but I can still hear that noise coming from my monitors. So can I reduce it with ferrite beads too?

Thanks for reading.
Old 1 week ago
  #2
Gear Addict
 

Ferrite cores (what I think you're talking about) are basically only effective at lowish RF frequencies, 100's of kHz through 10's of MHz. If the source of your noise is due to EMI etc. in that frequency range then they could help. It may well be useful to add them to other USB cables since you have some evidence that your computer is putting out some noise in that frequency range, based on the improvement you've seen.

Putting them on audio cables would be quite unlikely to help, in my estimation, since I rather doubt you have RF noise being emitted or picked up there. I'd guess instead perhaps there are some niggling grounding issues or ground loops. USB connections do not always fit very nicely into good analog grounding schemes.
Old 1 week ago
  #3
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Richard Crowley's Avatar
 

Ferrite beads will do NOTHING against true "hum" (i.e. 50/60Hz power mains frequency + harmonics)
They MAY have some effect on higher frequency noise.

I would never filter what goes into the monitor speakers in any way.
That is your last line of defense and monitoring exactly what your audio signal sounds like.
If you filter you monitor speakers so that they sound OK, but the noise remains in your mix, you are shooting yourself in the foot.

Do you hear this noise from your monitors....
1) When no audio cable is plugged into them?
2) When the input connectors are shorted out?
3) When the audio cable is plugged in but not connected at the source end?
4) When the audio cable is plugged in and shorted at the source end?
5) When you plug the monitor power mains cable into the SAME mains plug as the other gear vs. a different plug (circuit)?

Only by doing that kind of differential diagnosis procedures can you determine the source of the noise.
And only by knowing the source of the noise can you intelligently apply noise mitigation methods.

Without a sample recording, we don't have any way of knowing whether the noise you are asking about is really "hum".
It seems unlikely to be hum if ferrite beads are affecting it.
Old 1 week ago
  #4
Here for the gear
Thank you for your replies.

So, to begin with, I know the source of my problem: my laptop and its switching mode PSU. It's that very characteristic 50 Hz hum coming out of my speakers, and it gets amplified when I run resources-heavy applications on my computer (like my DAW for example).

Like I said, the problem is not present in the recordings, or when monitoring on headphones. I got round to it using hum removers between my hardware synth and my interface inputs. It's only coming from my speaker monitors and only when my interface is connected to the computer via usb. For info, I use a Presonus AR16 mixer as an audio interface and it has its own PSU, so it's not powered by usb. That allows me to have the interface still on while not hooked via usb.

Attached below are 2 recordings of the output noise of one speaker, holding a microphone in front of it. Output faders of both the return track (from the computer through the usb cable) and master level (to the speakers) are at unity gain during both recordings.
1st one is when using a usb with no ferrite bead (or core if you prefer: the little cylinder at one end of the cable), 2nd recording is when using one with ferrite bead. One can hear the slight improvement, though the ground hum can still be heard. But you may be right, what's being removed is not actually the 50 Hz hum itself, though it feels like it's weaker.
Attached Files

Hum1.wav (4.20 MB, 143 views)

Hum2.wav (3.34 MB, 139 views)

Old 1 week ago
  #5
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Richard Crowley's Avatar
 

That sounds like "computer digital hash".
It does not sound like "hum" or anything to do with "ground loop".
As you say, laptops are notorious for this kind of digital hash noise.
Does it produce the same systemic noise when operating from battery?
With the external "power brick" completely disconnected from everything including mains power?
Old 1 week ago
  #6
Here for the gear
This I cannot test anymore unfortunately. My battery is completely dead. I'm saving to upgrade my system to a rack-mounted computer with linear PSU anyway, that should greatly improve things. I was looking for a temporary fix.
Old 1 week ago
  #7
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Richard Crowley's Avatar
 

You will have a hard time finding any kind of linear computer power supply.
I am not sure I have seen one in 30 years.
Even high-end audio gear now has switch-mode power supplies (SMPS).
But SMPS are nice and quiet if the whole circuit is designed properly.
Alas, there are no portable/laptop/notebook computers that were designed to accommodate audio properly.
Even desktop/tower/rack-mount computers often have too much hash inside the box to use internal audio interfaces.
Which is why external (typically USB) audio interfaces are so popular. For both fixed and portable computers.
Old 1 week ago
  #8
Here for the gear
Really? I thought pretty much every desktop computer game with linear psu. That's a revelation now.
Would a power conditioner fit the job then?
Old 1 week ago
  #9
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Richard Crowley's Avatar
 

Quote:
Originally Posted by tomatoKetchup View Post
Really? I thought pretty much every desktop computer game with linear psu. That's a revelation now.
Linear power supplies are becoming more rare every day. SMPS are taking over in virtually every application.

Quote:
Would a power conditioner fit the job then?
No. Because the noise is generated well downstream of any power conditioning.
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