The ABCs of HDMI Cables

Digital standards and technologies improve at an exhilarating pace. Newer and better technology is a good thing, but the downside is that many of us amass a huge variety of cables and connectors over time. Knowing how, when, and why to pick one connection type over another can be overwhelming.

Fortunately, as we move into an increasingly digital world, options are getting simpler and more straightforward, so a little information can go a long way towards clarifying your best choice. HDMI is the gold standard today, but not all HDMI cables are created equal.

What is HDMI?

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HDMI stands for “High Definition Multimedia Interface.” Just as the name suggests, HDMI functions by passing high-quality audio and video signals. Unlike the DVI interface that came before it, HDMI can send uncompressed video signals along with either compressed or uncompressed audio signals using a single cable (DVI could only send video). This versatility allows the user to simplify their setup by using only one cable for both audio and video without sacrificing signal quality.

HDMI cables also carry a Consumer Electronics Control (CEC) signal that allows HDMI-connected devices to control each other. The CEC signal enables the use of a single remote control to operate all the connected devices. Some HDMI cables are available with an Ethernet channel as well, which allows high-speed bidirectional data transfer.

HDMI Connector Overview

The HDMI standard includes five types of connectors, referred to as types A-E:

1. Type A: This is the standard HDMI connector (13.90 x 4.45mm), available on virtually all HD TVs. It has 19 pins, the bulk of which carry video, audio, and timing data and are assigned in groups of three: a positive/negative pair with a pin that acts as an interference shield between them. The remaining pins carry information like the CEC signal. There is enough bandwidth to carry all modes of video up to 4K. These connectors are compatible with the older DVI-D connector.

2. Type B: This type was designed as a dual-link version to increase data speeds but was never implemented. Single-link HDMI speed eventually outstripped the speeds possible in the dual-link concept.

3. Type C: Often referred to as “mini HDMI,” this connector is considerably smaller (10.42 x 2.42mm) and retains the 19-pin configuration, though it swaps the position of the positive signals with their corresponding shields.

4. Type D: Known as “micro HDMI” and roughly the same size as a micro-USB connector (5.83 x 2.20mm), Type D also has 19 pins, but a configuration different from either Types A or C.

4. Type E: Used in automotive applications, Type E has locking tabs to keep the cable inserted during vibration in its environment. It also features a shell to protect against environmental hazards like moisture and dirt.

HDMI Pinout

The standard Type A connector has, as mentioned above, 19 pins. Below is how a 19-pin HDMI Type A connector works:

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- Pins 1-3 carry Data channel 2 (+/ground or data shield/- respectively)

- Pins 4-6 carry Data channel 1 (+/ground or data shield/- respectively)

- Pins 7-9 carry Data channel 0 (+/ground or data shield/- respectively)

- Pins 10-12 carry the clock channel that synchronizes the signals (+/ground or data shield/- respectively)

- Pin 13 is a CEC channel allowing devices to control each other

- Pin 14 has no current use

- Pins 15-16 carry the Display Data Channel (DDC) which communicates extended display ID information

- Pin 17 is the data shield for pins 13, 15, and 16

- Pin 18 is a low-voltage power supply (5v)

- Pin 19 is the Hot Plug Detect, and it monitors power and plug/unplug events

Mini HDMI Type C: In the Type C “mini” plug, the overall pinout is the same, but each pair’s positive signals exchange places with the corresponding shield/ground (pins 1 and 2 change places, for example). Additionally, the ground for CEC/DDC is on pin 13, CEC data is on pin 14, and the additional pin is on 17.

Micro HDMI Type D: The Type D “micro” plug also rearranges the order of the pins but retains the same number of pins as well as their same basic functions.

Note that the (relatively) new USB-C connector has an HDMI-compatible alternate mode. This mode does not require active converters. Instead, the HDMI protocol’s full functions are mapped directly to the pins of the USB-C, allowing a native connection with USB-C devices.

HDMI CableTypes

Let’s move beyond connectors, but only by an inch or two. HDMI cables come in several types, divided into category 1 (for standard speed cables) and category 2 (for high-speed cables).

HDMI Category 1:

1. Standard (Category 1): This is the baseline HDMI cable, certified to carry resolutions up to 720p or 1080i, along with high-definition surround sound and certified capable of 742.5 Mbps/channel.

2. Standard with Ethernet (Category 1): Identical to the standard cable, this cable adds an Ethernet channel to allow device networking and shared internet connections.

3. Standard Automotive (Category 1): These meet the same signal requirements as the basic cable, and they’re designed for automotive applications.

HDMI Category 2:

1. High-Speed (Category 2): High-speed cables are ideal for use at higher resolution (1080p+) as well as emerging technologies (such as 4k and 3D video). High-speed cables are certified capable of 1.65 Gbps/channel (without equalization) and 3.4 Gbps/channel (with equalization).

2. High-Speed with Ethernet (Category 2): These function like regular high-speed cables, but also allow device networking and internet connection sharing.

Comparison to Other Technologies

So how does HDMI compare to other current technologies?

Analog versus Digital: Since HDMI is a digital technology, it doesn’t suffer from some of the problems that plague analog solutions. For instance, the build quality (and associated price) of analog audio cables can affect performance greatly, but this isn’t true for HDMI. All HDMI must meet the same standards, and they don’t suffer signal degradation the way that analog connections do.

Analog Audio: Analog home audio standard – RCA cables – offer high-quality sound (assuming they’re well-made and in good condition) but are limited to stereo – they don’t transmit the surround sound signals that are ubiquitous in modern HD audio-visual environments. On the other hand, analog connections are still king for live sound, so HDMI is typically not found in live sound applications.

DisplayPort: Perhaps the most similar connection to HDMI in terms of functionality, DisplayPort is another digital, multi-media interface. Users typically choose DisplayPort for computers, not home media devices. It lacks the CEC controls of HDMI, but it’s capable of sending multiple A/V signals to separate devices, making DisplayPort very well-suited to computing tasks requiring multiple display setups.

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Which HDMI Cable Do I Need?

All HDMI connectors transmit the same information, and they do it equally well.

The only essential difference is which size connector you need: standard (A), mini (C), or micro (D). Virtually all full-sized home electronics (televisions, audio systems, etc., as well as Raspberry Pi modules) utilize standard connectors. Portable electronics like tablets, DSLR cameras, and Raspberry Pi Zero use mini connectors, while micro connectors are limited almost exclusively to small portables (cell phones with an HDMI output, for instance).

When it comes to the cable itself, you either need 1080p+ (high-speed) or something lower standard. Lastly, decide whether you want to share an internet connection and networking capabilities (with Ethernet) or not (without).

HDMI Limitations

HDMI reduces cable clutter and makes high-definition connections simple, but it isn’t perfect. HDMI’s greatest limitation is its twisted-pair construction, which makes it prone to performance problems over long distances. The longer the cable run involved, the greater the signal degradation, and there’s even the possibility of time differentials in the main data signals (either between pairs or between members of the same pair). You can resolve this by using HDMI extenders, (for a category 2 HDMI cable, install extenders every 10m) but this complication may prove to be a significant drawback in large-scale applications.

HDMI’s other weakness is that it is not well suited to driving multiple devices simultaneously. In the case of video displays, HDMI can’t send multiple signals to separate devices (like DisplayPort). For audio, HDMI can’t send multi-channel surround and stereo signals simultaneously, so you will run into problems in multi-room setups with differing equipment in each room.

A Few Conclusions

HDMI is a great protocol for tidying up simple AV systems. It can, however, run into problems in large-scale setups due to the distances involved and its inability to drive multiple environments simultaneously.

In complicated systems, you’re better suited using a coaxial cable for longer runs. DisplayPort is the practical choice for driving multiple displays. Finally, very high-quality, precision-manufactured analog audio gear will still be the best option in many commercial audio setups, especially for live sound.

 

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