by Kevin O'Brien on 05/19/2012

***UPDATED 05/18/2013***

We wanted to update this article as a lot of things have happened since we first posted it. Some basic principles have now been laid out as we've had more time to test our theories and see how USB devices behave under certain circumstances. We're pretty sure there are a lot of facts floating around out there that just aren't true. What's a data-only USB cable? When do they come in handy and can I use them with my equipment? Do they make a difference in terms of sound quality?

First off, what is a "data-only USB cable"? A data-only USB cable is a cable that only contains the + and the - data leads. It does not contain the +5V power lead. lt SHOULD contain the ground lead. This type of USB cable is what is known as "Data-Only". You CANNOT just assume since your USB device is plugged into a power source that you do not need the power lead on your USB cable! That is just plain wrong.

All this depends upon which USB input receiver your DAC is implementing. A lot of USB DAC's are going with the XMOS USB input solution. Just as many are opting to use M2Tech's OEM USB input solution. Other manufacturers are choosing to use the Tenor USB input chips. An extreme minority are using the Via USB input chip. And lastly, the C-Media USB input board is also just hitting the audiophile USB scene. Another very cool thing we are starting to see is designers creating their very own custom USB input boards! In this case, you'll need to talk to the designer to find out if he or she is using USB power.

If you are planning on using a data-only USB cable, your USB input device may contain the M2Tech USB input board or possibly the Via board. If it contains any other USB input method mentioned above, it will most likely run on the 5V USB power bus. The few main exceptions to that rule are the Ayre Acoustics QB-9 DAC and the Auralic Vega DSD DAC. These units employ the XMOS USB input chip. The XMOS chips in these instances get their power from the power supplies inside the DAC's instead of from your computer's USB bus. Also if you own an Audio-GD DAC, which implements the Via USB solution, it's best to contact King Wa directly to see if your DAC uses power from your computer's USB bus or not. Every other DAC (that we know of) that employs the XMOS, Tenor, and C-Media chips gets its power from the computer's USB bus. Use this rule to figure out if your DAC could benefit from a specialized USB data-only cable design.

We offer our current 'Reference' YFS USB 2.0 interconnects in a 'Data-Only' option, a 'Standard' option as well as a 'Dual-Headed' or 'Split' option. The 'Data-Only' USB cable is just like the name sounds. This is your typical USB cable design with the +5V power lead removed. The ground lead is intact. The 'Standard' option is the conventional USB design with all 4 conductors intact. The YFS 'Dual-Headed' or YFS 'Split' Ref USB cable along with our YFS PS-5 power supply are specifically designed for DAC's using the XMOS, Tenor, and C-Media USB input chips. This design isolates the data leads from the power leads until the two meet at the DAC's input. It doesn't seem at first glance that this split cable design should elevate performance. We didn't believe it either so we tried it and sure enough there was an audible difference between the conventional USB design and the 'Split' design. Isolating the data and power leads appears to limit interference between the two which results in deeper, wider, more accurate soundstage and more separation between instruments and overall better presentation of the music.

We have compiled a list of known DAC's that will benefit from the 'Split' USB cable design. This list is not complete and we'd appreciate it if our readers could help us complete it as time moves forward.

 

USB Bus Powered DAC's/ SPDIF Converters:
 

SPDIF Converters

Anedio U2 SPDIF Converter
April Music Stello U2 24/96 USB Link
April Music Stello U3 24/192 USB Link
Audiophilleo 1 & 2
Bel Canto USB Link
Bel Canto mLink
Bel Canto uLink (NOT Bel Canto REFLink)
Berkeley Audio Designs Alpha USB
Bravo USB to S/PDIF Converter
Channel Islands Audio Transient MKII USB Converter (without 5V PS)
Firestone Audio SPDIF converter
Lindemann DDC
M2Tech HiFace TWO
Musical Fidelity V-link I / II / 192
Resonessence Labs Concero
Sonicweld Diverter HR
SOtM dx-USB HD
Soulution 590 USB converter
Stahl-Tek A.B.C.
Wavelength Audio Wavelink HS


DAC's

Abbingdon Music Research Digital Processor 777
Aesthetix Romulus Transport/ DAC
Aesthetix Pandora DAC
Anedio D2 DAC
Apogee Mini-DAC & Duet 2
April Music Eximus DP1
Atoll DAC 100
Audionet ART G3
Audio Research DAC 7
Avid Pro Tools 9 & 10 Mbox Mini
Bel Canto DAC 1.5
Bel Canto DAC 2.5 (NOT Bel Canto DAC 3.5 - NO USB Input)
Benchmark DAC1 USB (Original Version - Latest DAC1 is NOT compatible)
Benchmark DAC2 HGC USB
Beresford USB DAC TC-7520
Bricasti Designs M1 USB DAC
Bryston BDA-1
Bryston BDA-2
Burson Audio DA-160
Burson Audio Conductor
Cakewalk UA-25EX CW USB Audio Interface
Calyx Femto DAC
Calyx DAC 24/192
Cambridge Audio DAC Magic
Cambridge Audio DAC Magic Plus
CEC DA53
Centrance USB Devices
Chord QBD76 (NOT Chord Cute HD)
dB Audio Labs Tranquility SE DAC
dCS USB Capable DAC's (All Models)
Devilsound DAC
Digidesign MBox 2 mini
Edirol UA1A USB Powered Audio Interface
E-MU 0204 & 0404
EMM Labs DAC2X
ESI Dr. DAC nano
Firestone Audio Fubar II & III
Focusrite Saffire 6 USB & Scarlett 2I2
Hegel Hd2
HOTaudio Extasy USB DAC
HRT Music Streamer (All USB Bus Powered Models)
IBUKI Musica DAC's & Amps
Jolida Glass FX DAC I / II / III
Jolida Fusion DAC / Transport
Kingrex USB DAC's & USB Amps
Korg DS-DAC-10
Lindemann DAC 24-192
Lindemann 825 HD Disc Player
Marantz NA7004 Network Audio Player/DAC
Matrix Audio X-Sabre DAC
Maverick Audio - DAC TubeMagic D1 & D2
M-Audio Fast Track USB & Fast Track C400 & C600
Meitner Audio MA-1 DAC
Meridian Audio Explorer [Headphone Amp/USB DAC] (XMOS)
Metrum Acoustics Octave MkII (NOT MkI or HEX)
Musical Fidelity V-DAC (NOT the V-DAC II)
Musical Fidelity M1 DAC
NAD M51 USB DAC
Native Instruments Komplete Audio 6 & Traktor Audio 10
Northstar USB DAC 32 Essensio (NOT Northstar 24/192)
NuForce Icon 1 & 2 HD HDP uDAC-2/ uDAC2-HP
Peachtree Audio novaPre
Peachtree Audio Grand Pre X-1
Perreaux Audiant DP32/ Audiant 80i
Presonus Audiobox 22VSL & Audiobox USB
Primare DAC30
Pro-ject USB Box
Propellerhead Balance
PS Audio Digital Link III
PS Audio PerfectWave DAC
PS Audio NuWave DAC
Rasteme Rudd14 USB DAC
REGA DAC
Resolution Audio Cantata Music Center
RME Babyface
Schiit Audio DAC's (All Models)
Silverstone USB DAC
SimAudio Moon 100D
SimAudio Moon 300D
Sound Devices USB Pre 2
Stahl-Tek Ariaa DAC
Tascam US 122L / 122 MKII / 144L / 144 MKII (All USB Bus Powered Models)
Teac UD-H01 DAC
Totaldac D1 Reference
Trends Audio DAC
Triode Corporation TRV DAC 1.0
Wadia 121 Decoding Computer
Wadia 151 PowerDAC Mini
Woo Audio WA7 Fireflies
Wavelength Audio (All Models)
Yellowtec PUC2


Please add to the list if possible. If you have indeed tried a DAC and you're certain it uses USB power and it's not on the above list, contact us and we'll add it...

We hope we have shed a little more light on the 'data-only' USB cable and if we answered at least one of your questions we have accomplished what we set out to do here. THANKS for reading!!!

 -YFS Design Team

 

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by Mike O'Brien on February 2012

First, this is a layman’s discussion, no equations, no statistics.  There are plenty of good technical documents on the web covering the USB standard, electrical requirements, and testing. 

Digital data is composed of square wave pulses having fast edge transitions used to transmit data (1’s or 0’s).  How accurately the data is transmitted is a function of the transmitter/receiver circuitry and connecting cable.  Equalization of the interfaces (adding defined poles and zeros to the circuitry transfer functions) minimizes reflected waves in the cable and increases noise immunity of the system.  Keep in mind that data integrity is always compromised during a transmission.  This can be attributed to circuit timing and voltage variations (jitter), external noise, EMI, and physical cable limitations.  As speed goes up, Bit Error Rate (BER) tends to go up along with it.  Commercial error rate test instruments are available for testing device transmit/receive Bit Error Rates (BER).  They provide predetermined types of data maladies (random jitter, sine wave noise interference, sine jitter, etc) but they don’t test cables directly.  Cable effects must be evaluated as changes in performance of a complete system.  It is difficult to assign a meaningful number to cable integrity since BER is inherently a statistical measurement.  Any data system uses error correcting codes to reduce the effects of corrupted transmitted data.  Since this “check and correct” step is an algorithm, it requires time, which implies data must be buffered, corrected, re-buffered and then clocked out.  Too many errors can cause time delays in the output data stream.  One way to maximize data integrity is to minimize waveform distortions in the transmission link.  Sonic affects due to lost or contaminated data will depend on both the host and the peripheral device which is why a USB cable may “sound” different when used with different sources and DACs.  Sometimes lower bit rates will actually sound better than high resolution source because fewer data errors occur during data transmission process.  Matching data rates can be critical, especially with lower end equipment.

So anyway, how do we design a digital cable?  Well, let’s think about what we need to do. Even “digital cables“ are actually high speed analog transmission lines as far as the electrical signal is concerned.  The digital cable affects data transmission by distorting the square wave pulse, reducing the amplitude, causing phase (time) delay, and coupling noise into the data stream.  This ultimately leads to detection threshold errors on the peripheral side of things which translates into lost or incorrect bits.  So our goal is to maintain signal integrity at high frequency (fast edges translate into high frequencies, remember our old friend Fourier).  The first step is to optimize cable physical geometry, including placement of conductors, shielding, and grounding. Transmit/receive termination admittance, cable distributed capacitance/inductance, and EMI/EMC are considered in the data channel optimization.  Power channel wiring employs shielded oversized conductors to reduce loses in longer cables.  Both channels have 93% silver plated copper braided shields.  One version also includes a 100% coverage metalized Mylar shield in addition to the braided shield (helps with EMI/EMC requirements but didn’t affect sound in our tests).  Separate shield for data and power channels reduces BER by decoupling power supply noise from the data channel.   A very important aspect of any cable design is the material choice, both conductor and dielectric.  Our material selection is based on years of experience in the aerospace industry where signal integrity and low noise are paramount.  Employing the proper dielectric (optimized dielectric constant /dielectric absorption) makes a huge difference in waveform integrity (and it’s NOT Teflon like most people think!).  Minimization of tribo-electric effects is also a major consideration when choosing a dielectric material for use in an acoustically active environment.  We have also investigated a variety of conductor materials ranging from cheap Cu/Fe to 5 nines silver.  If you think all the RG standard cables are alike, guess again!  There is a huge disparity in performance even though they have the same characteristic impedance.  Interestingly enough, we found that optimized impedance (distributed RLC) has a much larger effect than material choice for this application.  Even though the single crystal copper and pure silver may offer lower noise (very noticeable in low level analog) the effect is much less pronounced.  Would a silver conductor be better?  Yes, but marginally.  Any time a pure metal is employed as a conductor the inherent noise will be lower.  Unfortunately the wire must be soldered to some other metal so intermetallics will form (bad for noise), plus the connector may have several plated layers of dissimilar metals.  I highly recommend looking into the metallurgy of soldering, brazing, and welding, you’ll be amazed at all the bad “stuff” that forms in a connection, pretty scary!

Anyway, the upshot is that we feel we have struck a balance between cost and performance by taking into consideration physical construction and material properties.  Our acid test is to have the “old analog guys”, non audiophiles, and musicians listen for differences in musical presentation.  Here’s the catch; they don’t know what’s being changed during the test, only that something MIGHT change.  Eliminating the psychological bias is critical when detecting perceived difference.  Several theoretically superior cable designs ended up being disasters!  After all, engineering is obtaining the best possible solution within the bounds defined by available resources and cost.  It is possible to stumble on a decent design quite by accident, as they say, even a blind squirrel finds a nut sometimes, but we prefer to apply some science to find ours!

I hope I did not turn potential readers off with my technical overview, but instead brought to light some important variables in cable design that we have incorportated in our YFS designs. We are trying to let people know we didn't come up with our designs by "playing around" with different cabling/ shielding variants like some of the other guys. We used SCIENCE!

 -MOB

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