long usb-c cables with audio interfaces

[Bo Deadly]

Does anyone see an issue with using a 10 ft usb-c cable between a 2018 mac mini i7:

Mac mini (2018) - Technical Specifications

and a MOTU UltraLite mk5:

Specs | MOTU.com

In this particular scenario the mk5 is only usb-c 2.0 which is limited to 480Mbps so I'm thinking a 20Gbps cable should be able to handle the longer cables without problems. Am I ASSuming too much?

Here are some examples of 10 ft cables I'm looking at:

https://www.amazon.com/USB-Cable-3-1-USB-C-10ft/dp/B089FV33QX/ref=sr_1_2?crid=3TBXR8POJDIE6https://www.amazon.com/UseBean-Tran...t/dp/B0BN5M5R8Z/ref=sr_1_10?crid=3TBXR8POJDIEhttps://www.amazon.com/Twozoh-Trans...3/dp/B0BG83RX1Z/ref=sr_1_14?crid=3TBXR8POJDIE
There are also some 15 ft cables that claim to do 10Gbps.

What are your good / bad experiences using long USB cables with audio interfaces like this?

Any drop-outs / lost connections?

 

[Tubetec]

I cut into a USBC cable recently , it was the same as a standard USB1.1/2 , Red,Black,Green,white and screen .
There was something I read recently about substandard USBC cables being sold on Amazon ,
The proper USB c cable has larger gauge conductors for the power lines and extra conductors for data lines and power management .
Theres always a chance noise could couple between adjacent conductors in a cable , the longer the more chances of this occuring .
Ive been experimenting with applying battery power to audio interfaces via the usb connection , the interface works standalone as an analog preamp without any connection to the pc , noise in the analog path is increased if the USB data connection is made .
I also spliced up my own cable with one section from a USBC 4 conductor cable spliced into another section of USB 2 cable with battery power , the weird thing was my device defaulted to USB 1.1 .
The only time I experienced drop outs was in a USB C to USB A , that turned out to be a dodgy connection in the USBC end of the cable .
Im starting to think USB is sub standard for audio power , all the variables can effect different devices in different ways , dirty power from the pc has an impact on the noise floor .
I do have a 5m USB A male to female ,I never experienced any dropped connections with it

 

[Bo Deadly]

I must admit I don't fully understand why USB cables have problems with longer than 5 meters when you can run 10Gb ethernet ~50 meters. Characteristic impedance of USB cables appears to be 90 ohms vs 100 ohms for CAT6e and both are differential so I don't see how the driving circuitry could be much different. I can only guess that it has to do with the cable construction. Like maybe USB cables use more thinner strands for flexibility which equates to higher resistance / capacitance whereas ethernet cables are always stiff and chunky? Maybe ethernet compensates for errors with code but it seems to me that USB could do that too.

 

[gyraf]

Naa, there's a good technical reason for the limit:

USB hardware - Wikipedia :

The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost. When adding USB device response time, delays from the maximum number of hubs added to the delays from connecting cables, the maximum acceptable delay per cable amounts to 26 ns. The USB 2.0 specification requires that cable delay be less than 5.2 ns/m (1.6 ns/ft, 192000 km/s), which is close to the maximum achievable transmission speed for standard copper wire.

/Jakob E.

 

[Bo Deadly]

Naa, there's a good technical reason for the limit:
Wikipedia reads: "The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost."

Mmm. The requirement for commands to be answered within a certain amount of time is a self-imposed limitation that equates to a software protocol issue. Alternatively the code could perform some code handshaking that allows for long delays. I can only guess that they wanted the code to be very very simple.

Although I think there are other possible factors for the cable length limitations.

One is that USB uses ground lines whereas ethernet does not. Connecting grounds over long distances is probably one of the largest sources of noise as EMI will induce currents in those lines. Imagine the noise on the shield of a dangling 10m would-be usb cable. Probably multiple volts in the wrong environment. Ethernet uses magnetics on the data lines. At 10mbps speeds the magnetics could be very small but there are limits to how small you can wind a transformer and I don't think they're easy integerated into an IC (although maybe the PCB?). This equates to more parts, more board space, higher costs, ...

Another limitation to consider is that USB generally uses 26AWG whereas CAT6e uses a fewer strands (better skin-effect) of 23AWG which equates to significantly lower resistance.

 

[gyraf]

usb guarantees timing and packet order - tcp/ip does not, very different requirements

 

[Yash]

Did plenty of tests on USB cables and made a DIY USB isolator as well as a very clean Linear PSU for +5V several years ago. Same conclusion: USB is lacking for direct to DAC connections, at least around 2017 when I was doing that. Fortunately, there are good high-speed isolators nowadays, or you can choose to inject cleaner power, have a reclocker or what not.

 

[Tubetec]

Im getting good results lately with nicad cells replacing USB bus power , the 4x 4000mah cells sit at around 5.5v off charge , if you drain off around 200mah they drop to 5.25v then you get the bulk of the capacity out of them before they go below around 4.6v .
Im using an RC hobby style microcontrolled charger , it has a handy charge/discharge cycle mode so its easy to evaluate performance under different loads and charge currents .

The standard emergency lighting cells packs are readily available in 2,3,4,5,and 6 cells sizes . Im definately going to try them for a tube mic heater supply ,similar to the early Neumann stabilyte based units , only with much higher capacity than the 300mah of the originals ,
Some resistance in series with the heater is probably a good plan in any case as at switch on from cold the low heater resistance could draw substantial current which would be undesirable .

This is the place I got the cell packs ,
Emergency Lighting NICD , they have a couple of stores in the UK too ,
Guy in running the shop was definately an ex squaddie , very serious and matter of fact , he was fair and square about it when I returned the first set of batteries which had obviously sat on the shelf a long time , I definately would have come out second best if it had come down to hand to hand combat though.

 

[Wavelength]

3M max with ASYNC audio stuff. I have a Tektronix compliance USB test set and do a boat load of USB work. Anything over 3M needs to be optical like the Corning cable. The UAC/UAC2 protocol for any audio device is really clear about the turnaround time. Longer cables have a problem with overhang. It's the ghost signal when one end stops transmitting and the other one starts and the preamble is messed up by the remaining crap on the line from previous transmission.

If the preamble gets messed up then that whole packed could be flagged for errors. Plus the UAC/UAC2 is not error correcting so your digital signal can easily be tainted. Especially with higher sample rates or # of channels. Both of which increase the USB packet size. The larger that is the more errors you are going to get.

The other problem is ground loops. If your going 10ft you better plug everything into the same outlet or your going to loose up to 30dB of Signal to Noise. All my higher end products now have USB isolators on the input so that doesn't happen.

Gordon

 

[cyrano]

I must admit I don't fully understand why USB cables have problems with longer than 5 meters when you can run 10Gb ethernet ~50 meters.

Ethernet is transformer balanced and uses 4 pairs. USB is a direct electrical connection and only uses 1 pair.

 

[Newmarket]

Ethernet is transformer balanced and uses 4 pairs. USB is a direct electrical connection and only uses 1 pair.

IIRC that is correct for USB 2 but not USB 3. This is part of the problem in discussing. The USB standard(s) get hugely complex depending on application and implementation. Then there is the question of whether it's actually Thunderbolt via USB-C connector

 

[cyrano]

Yep. The USB consortium started screwing up after USB2. I'm trying hard to forget what came after.

These days, you can't tell what a cable does just by looking at the two connectors at the end...

Is it the only thing that drives cable sales?

 

[Newmarket]

I've stayed out of the details tbh and just dealt with remedial actions tbh. But I remember a former colleague showing me the USB spec' around 2006. It was at least an inch thick. He added that it "didn't include the USB OTG extensions
tbh I like to think back when the most I had to deal with was "proper" digital audio via AES-3 or -id, IEC950/spdif, tdif or ADAT.
There's also MADI but I never dealt with that on the bench.