USB cables and me

Discussion in 'DACs' started by gvl, Aug 7, 2017.

  1. SWL3600

    SWL3600 Super Member

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    My experience as well. I'm skeptical about everything and USB cables were no exception.

    I use Uptone's products with Curious Cables. They sound better than the silver Pangea cable I had prior. The Pangea and the Curious Cables sound better than all the cheap USB cables I have laying around.

    Night and day better? No. However, it is undeniable to me that their IS a difference in sound quality. The Curious Cables have a fuller, richer and smoother sound to them. Sad....but....true. The Pangea had the same qualities but not to the extent of the Curious Cables.

    Right now I'm checking out the USPCB hard adaptors from Uptone and so far they are promising. This weekend gonna do some comparisons.

    Guys that keep talking about 1's and 0's.......there's gotta be more to this. Too many people are claiming they are hearing the same things/differences. Perhaps going a little overboard, though.
     
    pete_mac likes this.
  2. mgosdin

    mgosdin Well-Known Member

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    677
    TBH, I'm the kid in Science class in middle school when the teacher demonstrated optical illusions and none of them worked on me. ( The lines are all the same length, what staircase? Don't see faces in clouds either. ) I've spent my professional career working with 1's & 0's, a lot. If the USB cables are made up to spec, regardless of what they cost or the materials they are made of, they will "sound" the same in a given component chain. If there is a difference in sound then one of the cables is out of spec.

    At the end of the day if it sounds good to you, and you can afford the cost if the cables are expensive, then it isn't worth it to argue about.

    Mark Gosdin
     
  3. gvl

    gvl Active Member

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    395
    Speaking of specs, I scanned through the USB 2.0 specification and I'd say 25% of the document is devoted to error detection, recovery, re-transmits, etc., and the document was written assuming the transmission media that is within the spec. From that, even being "within the spec", doesn't necessarily mean error free to me.
     
  4. dewdude

    dewdude I fix stuff.

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    Ok..I will start and say I'm also in the class that thinks digital is digital...and any differences in quality are down to how much you want to hear them.

    I look at it from this perspective:

    For starters, USB data transmission is a balanced signal over a twisted pair that is further shielded. The shielding on the cable should be sufficient enough to effectively isolate it from any noise getting inside the cable. Tack on to that the balanced signal over a twisted pair makes for a balanced transmission line. So any noise that does get in to the system is going to be common in both channels and will effectively be rejected. Of course, I know for a fact no USB cable is the same and how some are total garbage compared to others.

    So...I'm a ham radio operator. For the last year or so when I think about cables it's typically coax and transmission lines...and since I'm actually throwing some power in to them; I have to pay attention to things like shielding. But USB cables come in to play because I operate digital modes over HF/shortwave...which requires I have a way for my PC to trigger my radio to transmit. 99% of software is set up to use serial ports; so I have a USB to serial dongle plugged up to my machine. (BTW, the software basically pulls the RTS line to it's "high" state; which I feed through an opto-isolator to trigger my rigs transmit line). Let me tell you...HF/shortwave HATES our modern world. If you think RFI from your PC getting in to your audio stream would be a bad thing...how about the neighbor a quarter mile down the road with a plasma TV making your life hell? You quickly find out how cheap all your switching power supplies and electronics actually are by how much noise your radio puts out when you plug them in. I have actually made people in this house replace laptops because the model they had was just emitting so much RFI I couldn't work stations. I've been lucky is that I've found the right power supply for my computer with the right set of components that my PC doesn't emit any RFI. That was untill I got my dongle. Upon plugging that thing in..I was greeted with a very large amount of noise in my radio...which BTW sits maybe 2ft from my computer on a different wall.

    The shielding on that cable was maybe 4 strands of wire wrapped around the bundle...but even worse was that it was floating on both ends! There was no connection to the shell of the USB connector...so it was not grounded and was not effectively working as a shield. When I cut the board out of it's moulded rubber housing...I replaced it with a monoprice USB cable I'd clipped the end off of...the main difference was it had an actual braid of wire over everything and was connected to the USB shell. Guess what? No more noise! And in fact...when shielding is done properly..it's a faraday cage around your wires. And we all should know what a faraday cage does.

    So if this 12mhz oscillator's leakage is prevented by a proper shield on the USB cabling....I have to wonder how strong a signal you have to be next to in order to actually get in and cause interference in the first place. Plus...that interference would be common mode and rejected due to the data's balanced nature.

    No data mode transmission is error free!
    That's something that needs to be remembered. You will never avoid errors...all you can do is build in mechanisms to cope with the error in a sane amount of time. In fact, it's a bad idea to build any digital transmission system without a very basic error checking.

    But I'll leave with this. I listen to a lot of DSD on my DAC...and that data is pushed to the DAC doing what's known as "DSD Over PCM" (DoP). This is not a conversion to PCM as everyone incorrectly assumes (or likely wants to assume) it is. This is merely repacking DSD bits in to a WAV/PCM header. DTS famously did this on Laserdisc and for the DTS-CD format. This is done because there was no standard provision for sending DSD data to a DAC...so when it was done..it was done in some weird way that required special software. Even worse is some systems...like OSX...won't work with anything *except* a PCM stream. So the chipset designers/manufacturers got together and actually came up with the DoP standard. So instead of having 24 bits make up the PCM sample; you have 24-bits of DSD packed in order. All of your underlying software thinks it's working with a 176.4khz PCM stream...but the USB controller for your DAC picks up this is DoP...then tells the DAC to go in to DSD mode.

    DSD is vastly different than PCM. A corrupted sample in a PCM file just corrupts that sample. If you get bits getting wonky in a DSD stream...forget it..it has the ability to screw up the rest of the audio. DSD stores changes in the waveform where was PCM stores samples of amplitude waveform.

    If your system doesn't do bit-perfect to your DAC...DoP will not work. *Any* modification done to a DOP stream no longer makes it a valid DoP stream. If my cheap USB cable was causing degredation to the degree it would be audible...my DSD playback would be entirely broken. Since it's not, I know the bits are arriving at the DAC properly and that any error correction done in USB transport has come up with exactly what I should be getting.

    And if you're getting those bits properly to your DAC...then the medium in front of it shouldn't matter.
     
    bhunter likes this.
  5. gvl

    gvl Active Member

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    Is DoP sent over the wire using the isochronous transfer mode?
     
    Last edited: Aug 13, 2017 at 2:55 PM
  6. dewdude

    dewdude I fix stuff.

    Messages:
    2,987
    Location:
    Manassas, VA
    It's sent however the drivers send normal audio to the device. The only part of the process that knows about DoP is the software that generates the DoP stream, and the USB controller that interfaces with the DAC. Everything else just sees a 176.4khz (*for DSD64) PCM stream that it should pass unaltered.
     
    Last edited: Aug 13, 2017 at 3:30 PM
    bhunter likes this.
  7. SWL3600

    SWL3600 Super Member

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    I don't know what these cable makers are doing.....but I'll take the cable that makes my music sound better every time. As long as it's reliable and regardless if it is out of spec.
     

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