2. digital
  3. 159217-149317

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
herman
2,215 posts
 

@herman "Transmitting audio data in realtime is not the same as transferring TeraBytes of data files. You should look into it before making such statements."

Ok go ahead and explain me how it is different!! YOU should study about async digital communication, encoding and buffering... It’s obvious that you just plain don’t know.

https://darko.audio/2016/05/gordon-rankin-on-why-usb-audio-quality-varies/

I will defer to Gordon Rankin who I trust more than somebody angrily ranting on this forum


The three main USB transmission protocols are Bulk, Interrupt and Isochronous. Bulk (used for data transfer to a hard drive) and Interrupt are error-correcting. Isochronous (used for audio) is not.”

“Bulk and Interrupt are immediately NAK (negative acknowledgement). The receiver is designed to detect a bad packet immediately and the packet is resent.”

“For USB audio, the receiving device is basically translating a serial stream of data with a clock interwoven throughout. At the end of the packet sits some sort of block check. If the block check does not match the data then that packet is flagged as an error.”

“With Isoschronous USB transmission, packets are sent without any error correction / resending. But guess what? This is the USB protocol used for audio frames. The bad news is they are not error-free. The good news is these Isochronous frames are afforded the highest priority in the system.”


br3098
969 posts
 
@jaytor sed:
I think what @rixthetrick was getting at is that any signal on a cable is inherently analog
How's that? With all due respect, do you actually understand what makes analog signals analog and how digital signals are different. ABout the only similarity is that they can both use wire as a transport media. If a car operates on roads and a elephant walks down the same road, does that make the elephant a car?

herman
2,215 posts
 
Sorry, back to the difference in sending data over USB like we do with file transfers and audio uses.. to further my point above , despite what the angry poster says, .Audio and file transfers are different as file transfer protocols have error correction

 from Mojo Audio

The combination of asynchronous clocking and data buffering can remove jitter caused by packets of data arriving at irregular intervals, but it can’t correct corrupted data. Though asynchronous USB results in more liquid, more resolving, and more musical sound, if it isn't bidirectional, it has no error correction, and can not assure uncorrupted bit perfect data.

herman
2,215 posts
 
@jaytor sed:
I think what @rixthetrick was getting at is that any signal on a cable is inherently analog
How’s that? With all due respect, do you actually understand what makes analog signals analog and how digital signals are different. ABout the only similarity is that they can both use wire as a transport media. If a car operates on roads and a elephant walks down the same road, does that make the elephant a car?

It depends on how you look at it. "The only similarity is that they can both use wire" isn’t quite right.

Digital is by definition binary.... high/low, 1/0, true/false, whatever. Electrically, those 2 states can be represented by 2 different frequencies, 2 phases, etc. . With USB those 2 digital states are 2 voltage levels. Analog information is represented by constantly changing voltage levels with an infinite number of possibilities.

So yes, they are the same in that both analog and digital information are represented by voltage levels. Since the digital voltage level can’t change instantaneously (a perfect square wave) it bears some resemblance to an analog signal’s infinite voltage levels.

However, does any of that really matter? With analog, errors are a given. It is impossible to maintain 100% accuracy throughout the analog chain. On the other hand, digital errors are very, very low and in a well designed system, for all practical purposes they are zero.

In any case, it is a red herring that distracts from the topic of whether or not USB sucks

BTW.... it does not
antigrunge2 OP
1,331 posts
 
No piece of metal wire can perfectly render a square wave from a digital source (i.e. 0-1) You have to contend with reflections and other distortions (e.g. IR frequencies) which have to be sorted at the receiving end. In that sense the actual wire transmission can be argued to be analogue.
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