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How to stop USB noise in my DAC from my Laptop (mac)

Discussion in 'Sound Science' started by indigo bob, Jan 27, 2017.
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  1. Indigo Bob
    Are these what you are talking about?
    I don't want to go cheap if it's not going to work.

    Noise is still present when all is on battery power.
  2. pinnahertz
    Anything else connected to either device?  Other USB devices (printer, etc., amplifiers...)?
  3. pinnahertz
    I'd recommend you re-read your linked paper. It deals with data integrity, and EMF/RFI shielding. It doesn't address ground loops at all. In fact, grounding both ends of a shield is not only unnecessary to provide shielding properties, it's undesirable from the standpoint of ground loops.
    If they do (and I've never noticed that they do), it would be to prevent EMI/RFI radiation from the cable. Nothing to do with grounding.
    Glad to hear it. I doubt "all kinds" is completely accurate, but if that's your perception, go with it.
    He's welcome to try it, but it likely won't fix his issue, especially based on his last post.
  4. Arpiben
    Well it is also up to the author to unplug first his AC/DC plugs (free of charge) previous to buy any silver shielded cable :slight_smile:.
    First you need to understand the source of the problem then apply curative means. Shields are efficient if no current are circulating through them.
    I will suggest you to take advantage of Pinnahertz's experience rather than posting unrelated documents.
  5. WindowsX
    I'd rather trusted in USB specifications from manufacturers. The only scenario they suggest unshielded cable is for wiring inside usb controller with length under 3cm. For connecting between computer and USB device, they recommend shielded usb cable for most cases.
    Anyway, I once experienced hum and buzz on my dad's PC with USB audio interface and changing to shielded USB cable solved it. Ground loop on battery powered macbook isn't likely to happen unless he's using some hub switch with ground loop. I'm here only to suggest my solution that works and I think I've finished my job here.
  6. Indigo Bob

    No.  it would make this noise in the background with only the DAC connected to the laptop whether or not the laptop was plugged in.
  7. pinnahertz
    But for entirely different reasons. Noise from ground loops and noise from RFI/EMI are two different things entirely. You're blending them into the same thing.
    So, you have a single case where changing the cable resulted in a fix? Fantastic, there's a statistic for the books.
    Meanwhile, back on Earth where we face hundreds of issues with ground loops in broadcast and recording studios...and yes, home audio too...the reality is, a shielded USB is unlikely to solve the problem. Very unlikely.
    Agreed. And with his most recent post, I'd have to suspect one of two things: 1. We don't have the complete electrical picture, so anaylsis is hampered. 2. The noise source is something other than a ground loop between computer and DAC. Not to say it's not related to grounding and/or power supply, but I don't think we have the picture yet.
  8. pinnahertz
    At the risk of repetition...
    How is the DAC powered when connected to the computer, and noise is present?
    Does the DAC have the noise when not connected to the computer?
    Does the DAC have the noise when connect to a different computer?
  9. Arpiben
    For your information, in case you are interested,in Telecommunication shields are usually connected to ground only at one extremity.
    Now if apparently every device is battery powered and nothing else is connected to either devices we have little chance to face a ground loop issue.Agreed.
    I have no doubt also about how you solved your Dad's issue. But in that case the interferer should have had its origin outside PC.
    If the noise source is inside MAC, a shield will not remove it.
  10. WindowsX
    I never once agreed with assumption about ground loop. OP made it clear that macbook runs on battery power with only USB audio alone. It's unlikely to be ground loop problem. If anything, macbook or usb audio device may have problems with USB audio implementations.
    Also, shielding isn't only for EMI/RFI protection. Connecting ground chassis between device can reduce interference inside unit with proper designs and some documents recommended to connect shielding to both sides. Let's see if using shielded usb cable will solve it. It's only $5.
  11. pinnahertz
    The OP's info was several posts in coming, in fact, still incomplete.
    Possibly, but the typical problem you have with a Mac and a USB device results in no audio at all, or horribly distorted/noise audio from a mismatched sample frequency.
    You have an incorrect concept of what a shield is for and how it works. The shield is an electromagnetic/electrostatic shield blocking electromagnetic radiation with an electrically grounded surface, and blocking capacitive coupling by grounding the electrostatic field. Pin 4 of the USB connector carries ground, shield or not. Ground is essential for USB to work. The shield is not required for the ground connection to work. However, the shield must be grounded to function as a shield. The fact that it's grounded at both ends of the USB cable creates a problem: a potential ground loop. In audio, we often lift the ground connection of the shield at one end of the cable to prevent ground current from flowing in the shield.
    However, sometimes...sometimes...the shield may provide a lower resistance ground path between two devices that do not share an otherwise common ground. While you may think you've "solved" the problem with a shielded cable, what you've actually done is provided current path from one device to another that runs not only right next to the signal wires, but has no shield between it (being the shield itself) and the wires, thus having both capacitive and electromagnetic coupling to the signal conductors. This may or may not cause an issue, but the potential is there for slightly corrupting the transmitted data, possibly creating a jitter-like anomaly.
    The correct solution is to get both devices to the same ground potential without using the shield to do it. In most cases, it doesn't matter, because the ground current is low, coupling is low, and data isn't corrupted. But it's not the correct way to "ground" two devices together.
    I would suggest we continue to collect information from the OP before slapping a $5 "fix" on it.  
  12. Indigo Bob
    Here is a picture to help:
    (very simple usb DAC setups on two DAC's, the FiiO x3ii and the Martin HVA)

    Both basically have excellent background noise on their own, but when I connect each to the macbook air for USB-DAC playback, the background noise has this constant High pitched frequency that is tolerable, but only for a short period of time.
    My guess is that this is a quality with the mac in general since I have had this occur with macs.  I
    What do you guys think is the best way to fix the problem with the background noise?
    I usually use a longer USB cable to keep it as distant from the computer as possible.  When the HVA is close to the Mac, there is a static presence when the songs are ending and beginning and basically in moments in between where there is silence in the song.  However, this is an easy fix by distancing the HVA just a foot away from the position you see here in theses photos,
    BUT ...  the background noise problem, the almost quiet, but apparently present high pitched frequency, remains despite the distance from the laptop and seem so show no relationship with the distance it is from the laptop.  It literally sounds like there is an extra something (voltage/ energy) getting into the sound of the DAC's background noise and even into some of the music played.
  13. pinnahertz
    No, it's not a Mac quality issue. I'm a pretty hard-core Mac guy, I don't have these issues at all.
    Take a trip through your Mac's audio settings via Audio-Midi Setup, confirm your settings and make sure the DAC is getting what it expects too. This sounds a whole lot like a settings issue, like an error in sampling frequency.
    Before we look at distances, cable, etc., check those settings and make sure everything's a dead-on match, then go from there.
  14. Indigo Bob

    I don't think it's a mac quality issue.  What I mean is that it's something with the mac or the USB at least, but i think the mac....  anyways..
    For the HVA:
    IMG_0945.jpg ScreenShot2017-01-28at8.29.56PM.png
  15. Indigo Bob
    I think i accidentaly switched it to 48 kHz.  It is at 44.1 kHz
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