Audio and Video over USB...What Could Go Wrong?

Conceived more than a quarter century ago by a consortium of seven companies, primarily led by Intel, the Universal Serial Bus (hereafter, USB) has had a profound impact in helping us cope with our computer-dominated lives, from not long after its debut, continuing through its evolution to become a standard, and into our current era where data transfer speeds over USB now equal the latest HDMI specification. But USB does not enjoy a freedom from limitations – while many have been overcome, others persist ever-present. Everyday in business centers across the globe, USB-equipped devices dominate conference rooms and huddle areas, with voice and image performance paramount over simple data, presenting challenges for integrators. Let’s examine some of the issues in sending audio and video over USB, along with a remedy to USB’s designed-in drawback.
 
In the early years of personal computing, numerous, purpose-specific connector types such as parallel, DB-9, DIN, and IBM’s Personal System/2 were collectively required to cumbersomely connect peripherals with a computer to fashion a working system. Data transfer seemed a painful slog and limited cable lengths often necessitated a claustrophobic working environment. The intent propelling USB development was creation of a standard connection type for commonly used peripherals and where possible, to supply device operating power.

Introduced in 1996 as USB 1.0, it wasn’t until revision USB 1.1 in 1998 that industry-wide adoption took place and critical mass was achieved. Additionally, and perhaps most welcome, USB device evolution attained plug-and-play status, requiring none or minimal configuration interaction. The daunting maze of differing cable types to facilitate a functioning home or office system were winnowed down to a nearly singular form factor by USB, partnered with ethernet for a window to the world. As adoption became even more widespread, miniaturization for adaptation to compact devices took place, compounding connector types. USB is presently in its fourth generation (USB4), with technical specifications for an enhanced USB4 v2 released on October 18th, 2022.

The USB Implementers Forum (USB-IF) has deprecated (deemed technologically dated with further development and support suppressed) thirteen of the fourteen previous connection types with USB Type-C, first implemented with USB 3.2 in 2017, carried forward to be the foreseeable USB standard-bearer. While previous USB connection types no longer sustain additional refinements, their maturity assures use well ahead into the future for devices with modest data requirements.
 
USB Type-C and Intel’s Thunderbolt 3 and Thunderbolt 4 are identical in form factor with Thunderbolt essentially a superset of USB-C. While universal to a great degree, device capabilities determine the advantages each possesses.

To what extent each differs from another isn’t the purpose here, except to point out that with each series progression, capabilities increase exponentially.

Thunderbolt 4 represents the latest iteration and is differentiated by establishment of a minimum bandwidth requirement for PCle link, support for dual 4K or a single 8K display, Intel VT-d based protection against direct memory attacks, and power delivery. In step with the natural progression of technology, Intel has Thunderbolt 5 in the works, likely to debut early in 2023 and is said to be doubling data transfer rates up to 80Gbps bidirectionally, or as much as 120Gbps one-way with 40Gbps on the return side using a pseudo link training arrangement.  

While Thunderbolt is royalty-free, rigid Intel certification requirements for implementation will defer most non-Intel processor-based computer manufacturers to continue using the USB 9-pin, Type-A SuperSpeed connector.
 
With USB enhancements making high transfer rate capabilities available, what realistic applications might this present to commercial and residential integrators? Unfortunately, few practical custom installation scenarios beyond webcam and KVM control have emerged, despite USB’s meteoric climb into accelerated data transfer rates.
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Where these advancements handsomely reward particular end-users rightfully deserves acknowledgement. Content creation and post-production, from independent users to hallowed Hollywood facilities, was revolutionized by USB 3.2 with USB-C and now USB4 via Thunderbolt. It has become the simple, bespoke standard for close-proximity linking of a computer to a 4K broadcast monitor through an interface device but even more importantly, for simultaneous, blazingly fast reliable data transfer into a local high-capacity desktop storage device for subsequent rendering and file export.

Avid and competition gamers find Thunderbolt 4 docks consolidate wiring for gaming peripherals with no penalties in speed or latency.

In these examples, one of the main limitations for USB is indirectly apparent, that being it is widely known Thunderbolt 4 cables have a maximum length of 2 meters – a  miraculous increase from when Thunderbolt 3 first appeared at one-half meter.
 
Unique advancements have been made to conquer the inherent 5 meter passive cable limitation that has persisted since the release of USB 2.0 in early 2000. Innovative cable designs have made lengths as great as 25 to 30 meters possible however, they don’t provide a universal solution for all USB application issues. Some USB 3.0 designs employ fiber for distance extension but lack a provision to power endpoint devices where required. Additionally, they do not support USB 2.0 and lower USB versions. On occasion they may be confusingly proprietary, and manufacturing to fixed lengths may lend an untidiness to installations.

Signal-boosted active cables offer a partial solution but a 10 meter maximum for USB 3.0 limits use to compact locations when wall/ceiling navigation is factored in. USB 2.0 lengths up to 40 meters are possible but the effect to data transfer must be considered when specifying for an intended application. USB 2.0 High Speed has a maximum data transfer rate of 480 Mb/s… the spec everyone quotes, right? But this includes protocol overhead. Net data transfer rates for USB 2.0, particularly for a device which is bandwidth traffic-intensive, such as a USB 3.2 webcam shoehorned into a USB 2.0 backward compatible installation infrastructure, may have 320 Mb/s or less available to utilize for sending a motion-fluid, artifact-free image. If the distance exceeds the 10 meter limit for USB 3.0 cables and a USB 2.0 extension is required, the USB 3.0 device will operate at a USB 2.0 host speed. While pushing the envelope is admirable, please note that signal stability is often jeopardized.
 
An alternative to passive or active cables that attains distances as great as 100 meters using category cable was made recently available, through new innovative chipset technology implemented into HDBaseT Spec 3.0. While incapable of augmenting USB data capacity beyond 320 M/bs (HDBaseT Spec 3.0; HDBaseT Spec 2.0 supports up to 190 M/bs), it would seem inconceivable distance-related challenges for the most common integration installation projects would be unable to be met by this technology and the range offered.

This process does not use signal boosting in any way, rather “terminating” the incoming USB data (terminating refers to the USB protocol being subtracted, with only actual data bits transported). The USB data passes through the link in HDBaseT packets, and is then repacked into the USB protocol, transparent to the USB Host and endpoint device. It is compliant with USB 2.0 specifications, supporting Isochronous, Interrupt, Bulk, and Control USB transfers for up to seven USB devices, with the HDBaseT RX device on the far side of the link capable of providing hub functionality.

Portions of this process are accomplished in firmware with hardware acceleration used to enhance overall performance, giving integrators a prevailing solution to USB distance limitations for traditional Isochronous webcam with bidirectional video and audio applications. Trouble-free KVM Interrupt transfers for classroom, security, banking and control room projects may confidently be specified, installed and commissioned.
 
In 1G AV-over-IP systems with USB features, some facets of USB Interrupt transfer may be employed for KVM applications. 1G AVoIP systems are not blessed with a generous amount of bandwidth and many do not support USB 2.0 High Speed for time-sensitive devices such as microphones or digital cameras. Products which might, may not support simultaneous use for webcams with audio (typically not).

Recent to market newer chipsets provide more bandwidth to second generation AVoIP products from many manufacturers, but most still only provide support for one Isochronous transfer device. While some video conferencing bars may serve as a hub and possibly parse data through stream pipes to function as intended, anticipated performance would likely prove unpredictable and such devices are not recommended to be designed into 1G AVoIP systems.

Ostensibly, scenarios with single/multiple cameras with bidirectional audio and multiple viewing attendees have largely been handed over to codec-based IP systems such as Zoom and Teams.
 
From a humble beginning USB has come to dominate connectivity across nearly every electronics platform imaginable. While it hasn’t displaced HDMI for home entertainment purposes (Thunderbolt 4 cable length of 2 meters a primary reason) the time may come in the not too distant future when this obstacle is overcome. In the here and now, however, solutions exist for integrators to send audio with video signals across a room or across a soccer field, with reliability and predictability. In line with your company’s methods and best practices, always pre-test cables or devices to ensure performance and compatibility prior to specifying and site deployment while procuring products from reputable manufacturers that offer support and a strong warranty.    

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