Discovering a new DAC output on motherboard, worth it ?

Discussion in 'Computer Audio' started by Obieworld, Nov 7, 2018.
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  1. Obieworld
    Hi guys,

    I'm about to invest in a new motherboard for my PC (new build) and on the specific board (Gigabyte Z390 AORUS Master) I'm surprisingly discovering a new feature ! A USB 3.0 DAC-UP port ! (yellow ones)

    I do not find a lot information on it, actually almost nothing, I’m supposing this is a less noisy USB output dedicated for an external DAC, ok seems pretty cool. But is it worth it ? Will it replace my “Intona High Speed USB Isolator” already in my possession ? Those it worth maybe doing both ?

    Many thanks !!!
     
    Last edited: Nov 7, 2018
  2. selvakumar
    yes you are correct and its constant and stable 5v output and it passes direct to the pch
     
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  3. Obieworld
    Thx for your answer Selva !!
    Ok, now I'm sure what it is :) but is it worth it ? does this replace my “Intona High Speed USB Isolator” ? can I sell it ? or do I still need to put them for an extra-extra anti noise lol ? seems a bit too much if this port does the job well.
     
    Last edited: Nov 8, 2018
  4. PurpleAngel Contributor
    Try the new motherboard with the Intona plugged in and without the Intona plugged in, see if there is a worthwhile difference.
     
  5. Obieworld
    Ok thanks for the advice Purple ! I will certainly try this and make a self conclusion.
    I'm just suspicious about those features... can also be a gimmick as I never heart this before.
     
  6. voon
    How can a USB port be noisy? It transports digital data that has to come across a 100% accurate.
     
  7. Wiljen
    You need to read up a bit before commenting. just because something is digital does not mean it cannot be noisy, it just means that small levels of noise do not impact the interpretation of data as much as they would in analog systems.

    Think of it this way, in analog, the distance between 0 and 1 is measured in 1/1000ths and each step between 0 and 1 represents a different value. This means that any noise causes a change in the data being transmitted.

    In digital those same subdivisions exist but everything below 500/1000ths is interpreted as 0 and everything above 500/1000ths in interpreted as a 1 (arbitrary cutoff for illustrations sake - please don't shoot the messenger).

    Noise can be seen on a scope in all digital systems as even optical is not a perfect 100% on/off so you tend to see either a slope rather than a perfect vertical or you see saw teeth along the horizontals.

    So in digital, some small amount of electrical noise is compensated for by the assumption that anything below a threshold should still be thought of as a Zero. Larger amounts of noise can cause the system to incorrectly process the data as a 1 instead of a Zero.

    Now imagine this process happening thousands of times a second and that any one sample being wrong can be enough to produce audible change. An error rate of 1% is almost certainly unacceptable but not outside the realm of real possibility.

    Want to prove it, run your USB cable over a fluorescent bankers light between your source and DAC and listen to the results.
     
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  8. voon
    Hm .. is USB Audio different to USB data, then? I.e. no error control, handshaking or whatever (I'm not THAT USB protocol fluent here)? I can imagine issues if USB Audio is "fire and forget and do not check with CRC checks or whatever for the end result" ... I could imagine that for timing/real time problems. For computer data, a single 0 instead of a 1 is intolerable, hence the copy on the other side must be the same by 100% and there's usually systems in place to ensure that ... otherwise you'd have data loss across the board everywhere. I assume those have error correction for that reason, but maybe in audio that adds too much unwanted latency? Not sure there.

    EDIT: Some googling showed apost about Isosynchronous USB transmission, that indeed does exactly this ..... no use of error checking. Then you're right .. it could transmit a wrong bit. Doesn't seem to impact much in normal cases apparently, though http://www.realhd-audio.com/?p=5971
     
    Last edited: Nov 9, 2018
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  9. Wiljen
    Most USB data is not time sensitive and uses error correction, audio and other time sensitive data has none because re-transmission is not possible as the endpoint does not have a mechanism to resequence data in the buffer. In most cases the buffer size is too small to allow for retransmission and re-sequence (if it did have a way to do it) as by the time the re-transmitted data arrived its place in the order would have already passed.
     
    Last edited: Nov 9, 2018
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  10. voon
    Thanks :wink: something new to learn every day. It's obviously true, that digital does not automatically include errorchecking etc (same for UDP protocols etc I guess). It often is, therefore I didn't even think of USB Audio not using any CRC or somesuch, Thanks for the explanations. I assume in most situations it doesn't matter that much, given we don't usually carry bankers lights around for listening to music .. but I see a possibility in motherboard noise.
     
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  11. Wiljen
    The fluorescent lamp is just a quick way to about guarantee electrical noise. Other things that produce similar results happen more frequently.

    Problems with power are often passed into the system as most PC power supplies are minimally built to save cost. This means anything that causes the lights to dim or blink (turning the microwave or hair dryer on , an electric heat-pump or AC kicking in, a squirrel getting one foot on the line and the other on a transformer etc...) will cause visible noise if measuring the power output from the pc power supply. Since USB carries that same power on it, noise introduced via this mechanism is actually carried inside the cable so shielding doesn't help since it is being injected inside the shield.

    Almost everybody has a cell phone now and very commonly it is sitting on the same desk with your laptop. Cell and wifi antennas can and do interfere and cause noise on cables in many cases. Here sheilding an help since the interference is coming from the outside. Most usb cables are not heavily sheilded though and can be susceptible to placing a phone in close proximity.

    Other components inside the PC case that have magnets in their structures (pretty much all spinning disks) can also cause noise when in close proximity. (Placement of a hard drive immediately adjacent to or above the USB circuit may introduce noise into the circuit.
     
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  12. voon
    Probably correct. But I'm thinking about this: if in computer USB data transfer (not audio) these issues would be the cause of a lot of trouble often across the board, and thus forcing retransmission of data packets often etc, the whole USB standard we use since decades would be a complete failure with transfer rates being utterly underperforming. Which it doesn't (unless you have really crappy controllers on one side etc). Which tells me that USB works just fine in normal surroundings. Therefore I would assume there minimal influence of normal surroundings onto shielded USB cables. Or from within the source into the cable. Which leads at least me to believe that I don't think very expensive measures must be taken to make USB work for Audio.

    But doing galvanic separation on the motherboard of the analog audio circuitry/DAC on it would make sense.
     
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  13. Obieworld
    I didn't expect this whole discussion regarding my threat, but this information is priceless !! even if I knew the problem regarding the audio data transfusion of the USB, I was enabled to go trough all those specific details !!
    Thanks Wiljen and Voon ! I learned a lot !
     
    Last edited: Nov 12, 2018 at 10:05 AM

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