HDMI 2.0 and 2.1
HDMI is ubiquitous in the consumer AV market and is
widely used in professional AV. It is currently the de facto
standard for transporting uncompressed digital video over
relatively short distances. In addition to video, HDMI
transports compressed or uncompressed audio in stereo
or surround sound formats, as well as several control
signals that support HDCP handshaking, EDID, consumer
electronics control (CEC) and hot plug detect (HPD). All
this fits in a 19-pin connector made in sizes from standard
to micro.
HDMI 2.1, the latest revision to the HDMI standard,
pushes bandwidth from the previous 18 Gb/s to 48 Gb/s
to support 4K video at 120 Hz refresh rate, 8K/60, and
eventually 10K/120. The enhanced refresh rates produce
smooth, seamless motion and transitions when viewing
fast action, making possible several new features that
enhance the viewing experience:
• Variable refresh rate (VRR)—Reduces lag, stutter,
and frame tearing.
• Quick media switching (QMS)—Source devices
can switch resolution or frame rate without
introducing delays that cause stutter or blank
screens during switching.
• Quick frame transport (QFT)—Each frame travels
faster from source to sink, reducing latency
and producing a smooth, no lag experience
when viewing real time video content.
• Auto low latency mode (ALLM)—Automatically
sets the ideal latency for smooth, lag-free, and
uninterrupted content for applications ranging
from movies to real-time interactive virtual reality.
What about audio? HDMI 2.0 already has impressive
audio specifications. It allows 32 channels of uncompressed
audio capable of supporting sound formats up
to object-based sound fields like Dolby Atmos. HDMI 2.1
adds more audio capability through enhanced audio
return channel (eARC). Legacy ARC allowed simplified
cabling by back feeding audio from the display to
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a surround sound amplifier or sound bar over the same
cable delivering video to the display. But, ARC’s 1 Mb/s
bandwidth compromised audio quality because it used
audio compression and a reduced number of sound chan-
nels, often only stereo. Currently, eARC at 37 Mb/s can
handle uncompressed full resolution audio, supporting
all surround sound formats, including 32 channel
object-based audio.
To take full advantage of HDMI 2.1’s high bandwidth,
a new ultra high speed HDMI cable is required. HDMI 2.1
cables have better fabrication quality standards, better
materials and better shielding than legacy cables. Maximum
length for passive cables is 10 feet (3 meters). Active,
hybrid optical-copper cables are an option for long runs
up to 300 feet (91 meters). The legacy 19-pin connector
is retained, allowing backwards compatibility.
AV OVER NETWORK INFRASTRUCTURE—
UNCOMPRESSED VIDEO OVER TWISTED PAIR
Why Use Twisted Pair?
Most AV installations require running cables over long
distances inside walls and above ceilings. This can be
a problem with standard digital AV cable assemblies like
HDMI and DVI; the connectors are too large for conduit,
and field termination really is not an option for precision
connectors. Furthermore, most standard AV cables are not
suited for long distances. To meet this challenge, a consortium
of over 200 companies formed the HDBaseT Alliance
to establish a standard for point-to-point transmission of
uncompressed AV content over Cat 5e or above twistedpair
cable or optical fiber. HDBaseT uses active transmitterreceiver
pairs employing PAM16, which is 16-level pulse
amplitude modulated encoding to send digital signals
over Category twisted-pair or fiber cable that can be