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Making Sense of Thunderbolt 3 and USB-C

If you’re like me, making sense of evolving computer standards like Thunderbolt 3 and USB-C is confusing. These standards seem to change often and sometimes when plugging things in that ought to work, they don’t work at all. It’s all in the details. Here’s an overview of where we stand.

I bring this up because the Thunderbolt 3 and USB-C standards have an effect on engineers of all kinds — especially in the pro video and audio industries. Sweetwater, the pro audio dealer in Fort Wayne, Indiana, realized the confusion and prepared a good overview article on the these new standards. It is the basis for the information in this article.

Let’s start with the USB-C connector, which on the latest model computers is used with both Thunderbolt 3 and USB 3.1 for data and power transfer. This means the AC wall warts of the past won’t work. USB-C computers charge through the port. Standards like USB Type-A, Type-B, Mini-A, Mini-B, Micro-A and Micro-B connectors are also gone, leaving us with one type of connector.

All this is an attempt to simplify things. Yet, like everything else, you must learn the differences in order to not get burned. In the old days, each protocol had its own connector type. That’s no longer the case. USB-C, whose connector can be inserted on either side, is intended to be a universal cable and connector specification. It is very small and allows for smaller-size hubs.

Here’s an important thing to remember: The term USB-C describes only the physical cable and connector, not the data speed or charging capability. Many are confused by this and it can be a “gotcha.”

The Thunderbolt 3 logo on this USB-C connector means it is compatible with USB peripherals. Any Thunderbolt 3 port is also a USB 3.1 port.

The Thunderbolt 3 logo on this USB-C connector means it is compatible with USB peripherals. Any Thunderbolt 3 port is also a USB 3.1 port.

Because Thunderbolt 3 and USB 3.1 Gen 2 (the latest generation for USB) use the same connector, it’s not surprising that many people don’t know which is which. And, yes, there are significant differences between the two standards.

Thunderbolt 3 is currently the fastest data transfer protocol. It can transfer, if the device allows it, up to 40 Gbit/s with short cable runs (depending on whether you’re using passive or active cables) and 20 Gbit/s with longer cables. USB 3.1 Gen 2 tops out at 10 Gbit/s.

Thunderbolt is also bidirectional and provides four lanes for PCI Express Gen 3 and eight lanes for DisplayPort 1.2 connections. You can daisy-chain multiple Thunderbolt devices so they share a single Thunderbolt port. However, every USB device must connect via its own cable to its own port.

For audio editors, finding an audio interface with no perceptible latency, and/or need to drive multiple monitors or external high-speed graphics cards, Thunderbolt 3 is what you want. This is why new audio products, such as Universal Audio’s Arrow ($499), use Thunderbolt 3.

Thunderbolt 3 can connect not only to Thunderbolt-aware devices but also to older protocols like HDMI or FireWire via adapters. Thunderbolt 3 can also connect to USB devices.

Although USB 3.1 Gen 2 devices use an identical USB-C connector, this is solely for connecting to USB peripherals (some do support sending signals to DisplayPorts, but this isn’t guaranteed).

Remember this: A Thunderbolt 3 device with a USB-C connector has a Thunderbolt logo and is compatible with USB peripherals. So any Thunderbolt 3 port is also a USB 3.1 port.

Courtesy of Sweetwater

Courtesy of Sweetwater

A USB 3.1 device with a USB-C connector is not compatible with Thunderbolt 3 peripherals, only USB peripherals, unless the word “Thunderbolt” or a Thunderbolt logo is next to it.

Another advantage of USB-C is that there’s a companion USB-C specification called USB PD (Power Delivery). Devices using USB-C connectors, whether with Thunderbolt or USB peripherals, can deliver up to 100 watts of power for charging, or up to 15 watts to power bus-powered devices (including audio interfaces). The power delivery runs simultaneously with the data and is bidirectional.

Passive Thunderbolt 3-compatible cables can do 40 Gbit/s only at lengths of 1.6 feet or less and 20 GBit/s with up to 6.5 foot lengths. To do 40 Gbit/s at lengths up to 6.5 feet, users will need to purchase an active Thunderbolt 3 cable. On the USB 3.1 side, users need new and special cables that can handle the higher speeds. Older USB cables won’t work.

An active Thunderbolt cable contains transceivers in the plugs that regulate data transfer. A passive Thunderbolt cable does not — it’s just wires between connectors. A typical 19-inch Thunderbolt cable that comes packaged with gear will be passive and have slower transfer speeds at lengths greater than 1.6 feet.

Active Thunderbolt cables are more expensive than passive ones and will maintain higher speeds at longer lengths. Regardless of what cable is chosen, if users plan to power or charge gear with it, make sure it can handle the maximum expected current.

Both Thunderbolt 3 and USB 3.1 are “supposedly” electrically compatible with previous generations. But when using them, the user needs physical adapters. Thunderbolt 3 devices with a suitable bidirectional adapter can connect to previous-generation Thunderbolt ports, and USB 3.1 devices work with previous-generation USB ports. Of course, you won’t get the speed advantages with the older gear.

The word “supposedly” is used because backward compatibility is never guaranteed in the computing universe. It depends on the age, brand and type of computer being used. Always test these situations, because those “gotchas” are waiting at every turn.

OWC Thunderbolt 3 Dock.

OWC Thunderbolt 3 Dock.

Sweetwater also tells us that certain kludged together gear that you’d be skeptical of, often works. For example, Apple doesn’t make a Thunderbolt 3 to FireWire adapter, but it does make a Thunderbolt 3 to Thunderbolt 2 adapter, which users can then use with a Thunderbolt 2 to FireWire 800 adapter and a FireWire 800 to FireWire 400 adapter if the target device is FireWire 400. This one just happens to work. To find out, try it.

If a user is putting together a first class, Thunderbolt 3 system, it makes no sense to incorporate a bunch of older gear adapted to work with it. It is best to start clean and move your data to state-of-the-art drives as well. Yes, that means a brand new system. If not, piecing things together will be a hit and miss challenge.

Welcome to the new world of ever changing computer technology.

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