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USB sucks

USB really isn‘t the right connection between DAC and Server: depending on cables used, you get very different sound quality if the server manages to recognise the DAC at all. Some time ago I replaced my highly tuned Mac Mini (by now-defunct Mach2mini, running Puremusic via USB) with an Innuos Zenith Mk3. For starters I couldn‘t get the DAC (Antelope Zodiac Gold) and server to recognise each other, transmission from the server under USB2.0 wasn‘t possible because the server is Linux based (mind, both alledgedly support the USB2.0 standard) and when I finally got them to talk to each other (by using Artisansilvercables (pure silver) the sound quality was ho-hum. While I understand the conceptual attraction to have the master clock near the converter under asynchronous USB, the connection‘s vagaries (need for exact 90 Ohms impedance, proneness to IFR interference, need to properly shield the 5v power line, short cable runs) makes one wonder, why one wouldn‘t do better to update I2S or S/PDIF or at the higher end use AES/EBU. After more than 20 years of digital playback, the wide variety of outcomes from minor changes seems unacceptable.

Since then and after a lot of playing around I have replaced the silver cables by Uptone USPCB rigid connectors, inserted an Intona Isolator 2.0 and Schiit EITR converting USB to S/PDIF. Connection to the DAC is via Acoustic Revive DSIX powered by a Kingrex LPS.

The amount of back and forth to make all this work is mindboggling, depending on choice of USB cables (with and without separate 5V connection, short, thick and God-knows what else) is hard to believe for something called a standard interface and the differences in sound quality make any review of USB products arbitrary verging on meaningless.

Obviously S/PDIF gives you no native PCM or DSD but, hey, most recordings still are redbook, anyway.
Conversely it is plug and play although quality of the cable still matters but finally it got me the sound quality I was looking for. It may not be the future but nor should USB, given all the shortcomings. Why is the industry promoting a standard that clearly isn‘t fit for purpose?

Finally, I invite the Bits-are-bits naysayers to go on a similar journey, it just might prove to be educational.
antigrunge2
antigrunge2 OP
1,398 posts
 
Far from having ‘dissolved itself‘ I sincerely hope that this thread might lead serious designers to reconsider whether rather than using a low end, convenience consumer interface with all its known foibles to transmit high quality audio, one might usefully revisit more appropriate formats (optical, I2S, AES/EBU) to improve on what is at best an unacceptably wide range of outcomes with USB; I also note with a degree of puzzlement that members of the ‘bits are bits’ school of sitting on your ears are alive and well
djones51
4,947 posts
 
There are 2 reliable interfaces capable of transmitting DSD , ethernet and USB. If you're not interested then use optical, coax, or AES3. I2S was never intended for transfer between devices but on chip no more than an inch or two. There are a few DACs and streamers that have I2S just need to make sure what you're connecting to what is compatible. As far as jitter AES3 and coax will have more jitter than USB in well designed DACs. It's just the nature of the design, having the clock decided by the host like coax and AES3 causes more jitter than asynchronous transfer like USB. There's no puzzlement or spooky things at a distance bits are bits whether those bits are transferred by ethernet, USB, optical, coax or  AES3 it's the same bits.
herman
2,244 posts
 
My experience...
Cables make a huge difference for sure.
External clockers make a huge difference.

Jitter is the plague of digital audio. It can come from transports and servers. There are devices that go in the audio path to clean it up.

How do I know all this? I use my ears.

Not to discount your experience or your ears, but I have tried all manner of these devices and find they make no difference .. in my system.... to me.. I have tried among others

  • Uptone USB regen
  • Uptone EtherRegen
  • Cisco 2960 switch modified with a TCXO oscillator
  • Mutec MC-3+ USB reclocker with Mutec Ref 10
  • Roon Nucleus server
  • Innous Zenith server
  • Small Green Computer i5
  • various Mac Minis (which I currently use with the the Uptone linear DC/fan control mod)
  • Innous Phoenix USB reclocker
  • various USB cables
Of course I can’t say for sure why. It may be that I have wooden ears, or the fact that I use a pro audio DAC that has a very high quality clock built in that is also locked to a very high quality external 10MHz reference clock. The DAC is also a re-clocker that has outputs for both a high quality word clock and a de-jittered data stream if needed. .. but at the end of the day, just like you, my ears tell me what is important to me.

As for jitter from servers and transports.. Asynchronous transfer is designed to eliminate that. The DAC asks for data packets at its pace and clocks them on down the line using its internal clocks. Any jitter from the source is therefore disregarded so if you hear a difference using devices as above, in theory it is not because they reduced jitter. That said, I don’t doubt you hear something. I’m just saying that attributing it to jitter flies in the face of everything we know about how this stuff all works. I’m also pretty sure we don’t really understand how all of this stuff works, nor do we really need to if we are getting the results we want.

It would be interesting to use a source to feed an asynchronous DAC where you could vary the jitter and determine if you could hear it.


herman
2,244 posts
 
one might usefully revisit more appropriate formats (optical, I2S, AES/EBU) to improve on what is at best an unacceptably wide range of outcomes with USB;

I’m pretty sure that you will get an equally wide range of outcomes using these other formats.

And reading your initial post, the problems you had with getting a reliable connection are not inherently USB problems since millions of others have absolutely no issues getting a reliable connection. The fact that you finally got it to work with a particular USB cable tells me something else was amiss. The best sounding connection we can debate, but not being able to get the source to communicate with the DAC via USB is highly unusual.

I also have an Antelope DAC that I am extremely happy with although I do sometimes have to reboot my computer or the DAC to establish USB communication so maybe they do work better in a pro audio situation with that gear versus audiophile servers,  and I sometimes have to toggle the internal word clock from lower rates to the maximum rate to get sound output, but a minor inconvenience for the wonderful sound at a reasonable cost.
jaytor's avatar
jaytor
761 posts
 
As for jitter from servers and transports.. Asynchronous transfer is designed to eliminate that. The DAC asks for data packets at its pace and clocks them on down the line using its internal clocks. Any jitter from the source is therefore disregarded so if you hear a difference using devices as above, in theory it is not because they reduced jitter. That said, I don’t doubt you hear something. I’m just saying that attributing it to jitter flies in the face of everything we know about how this stuff all works.
+1.  It's quite possible that a device that purports to be a USB reclocker (any device that receives and retransmits USB is a reclocker) is reducing noise on the USB signal to an audible degree. But the notion that this is because it has less jitter on the USB connection makes no sense. 

I believe that there are still a lot of DACs on the market that sound better using legacy interfaces (spdif, toslink, aes3) but I contend that this is either because the source of these signals (transport/streamer) has a better clock than the DAC, or the DAC has a particularly poor USB implementation. 

There is no technical reason why a DAC can't be implemented with a USB interface that outperforms legacy interfaces. SPDIF, Toslink, and AES3 all have an inherent flaw in that they are prone to jitter because the clock is embedded with the data. No matter how much you spend on cables, the connectors themselves introduce impedance discontinuities which create reflections which interfere with the waveform. 

I'm not saying that legacy interfaces can't delivery excellent results. But from an engineering perspective, the cost to do so exceeds (perhaps significantly) the cost to achieve similar performance from USB (or Ethernet). I think it's only a matter of time before the industry has dropped the legacy interfaces in favor of USB (or some future asynchronous digital transport interface).
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