USB Cable Quality "Dither?"

Discussion in 'Recording/Live Sound' started by HammyD, Aug 10, 2006.

  1. HammyD

    HammyD Supporting Member

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    In reading literature/review on different USB A/D devices (Apogee Mini Me) it was mentioned that long cables can cause "dither." Is there a difference in quality of USB cables for audio applications, and could you offer advice on the best manufacturer? (Or is this another "Emperor's New Clothes audio myth!)

    Thanks Guys & Gals!
     
  2. flicker180

    flicker180 Member

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    signaling degrades over long distances. ideally, the shorter the cable, the better the signal integrity. with USB, it's transmitting power (in some cases) and data over the same lines, so, it's important that it recieves minimal EF interference. Generally, I use Belken cables or whatever i can get my hands on. I don't think there's any better way of doing things, so, i don't necessarily agree with the gold USB cables and such. Some cables will have a ferrous filter on one or both ends to "clean" some interference out. i guess that'd make for cleaner signal but again, your mileage may vary.

    dave
     
  3. HammyD

    HammyD Supporting Member

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    Thanks Dave!!! Fortunately my setup will permit use of a very, very short usb cable.
     
  4. landru64

    landru64 Member

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    since you have the opportunity to run it very short, how about you tell us what if any difference you perceive in a very short cable versus a longer cable, preferably the same brand/type... would be interesting to know.
     
  5. HammyD

    HammyD Supporting Member

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    I'll grab an assortment of cheap USB cables laying around here and then buy a Belkin and try and do some comparisons. I am still vacilating on the Apogee Mini Me USB and the MOTU Ultralite since my use will primarily be voice overs.
     
  6. flicker180

    flicker180 Member

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    to adequately reproduce this you'd need to transmit the same file (or file size) and have a wide variety of cables available. honestly, unless your cable is 100 meters long or whatever, you're not going to notice any difference. At an electrical level (one that i DOUBT you're going to want to test out) you'll notice noise, etc.

    btw, I believe that the USB spec allows for signal repeaters to be in place beyond X meters....I'll have to look that up.

    general rule of thumb: the shorter the distance, the less noise and interference.

    also, I usually use 1m USB cables. I need that length due to my workstation and test bench orientation. no issues.

    dave
     
  7. sysexguy

    sysexguy Member

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    "Dither" is not caused by poor cables.....so, so much for that article

    "Jitter" may be caused by poor cables

    Quick answers (non scientific): Dither is a randomization scheme introduced to the audio in order to smooth out our perception of softer passages (like reverb tails)

    Jitter is when error correction artifacts become audible

    google will help you find complete and detailed explanations as the above is an extreme oversimplification it will give a general idea as to what these terms mean

    Andy
     
  8. HammyD

    HammyD Supporting Member

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    Mea culpa! I may have confused "dither" and "jitter."
     
  9. elambo

    elambo Member

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    Definitely "jitter" and yes it can be a problem with long runs. Even short runs if the cable is of very poor quality.

    Digital audio is meant to reach it's destination at a very specific time. If you're working at 44100KHz then it's that many times each second. The increments of time between each 44100th/second must be very precise and equal. As the receiving device actually looks for the bit coming down the line it can sometimes be blurred. Kind of like a bus that opens its doors to let on passengers (this is actually how we got the term "bus" by the way) - if the door opens and the passenger isn't ready to put his foot in, you don't get all of the passenger on the bus. A digital clock tells the bus when to open the doors and when the passenger should be ready for the door to open. In audio, it means that the digital bit (either a 1 or 0) gets rounded off (this part is never easy to explain - I like the bus analogy better anyway).

    This is called jitter. Cables can cause it, noise in the line can cause it, poor digital clocks can cause it, etc. In any case, you want to do your best to avoid it. Audibly it shows up primarily as loose, undefined bass.

    I see this more in consumer grade audio (cd players and dvd players and ESPECIALLY computer audio cards), not so much in the prosumer or pro level stuff. Use a good cable and with the Apogee, which is already high end, you should be fine.
     
  10. HammyD

    HammyD Supporting Member

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    Thank you very much for the clear yet detailed explanation!!! Much appreciated!
     

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