HOME > Help & Info

Understanding HDMI®

In the past few years, HDMI® (High-Definition Multimedia Interface) has become the definitive standard for audio/video connectivity between various types of devices. HDMI ports are found not only on HD TVs and blu-ray players, but also on computers, smart phones, tablet PCs, video game consoles, and camcorders.

The HDMI interface is designed to transfer high quality, digital, multi-channel audio signals along with video at extremely high resolutions and color bit-rates. Being a digital signal with data error correction, it is much less susceptible to low-intensity radio frequency and electromagnetic interference, which would cause snow, ghosting, or other signal distortions in an analog signal.

Understanding HDMI® Video - Resolution

All HDMI cables and devices are able to transfer and process a basic set of video resolutions. This includes the basic Standard Definition (SD) video resolutions of 480i (NTSC) and 576i (PAL). It also includes some of the High Definition (HD) video resolutions, specifically 480p, 576p, 720p, and 1080i. Each of these numbers represents the number of video lines displayed on the screen. Obviously, the more lines in a display, the clearer and sharper the resulting video image will be.

Each of these resolutions has a horizontal number associated. The most important to know are those of the more common HDMI resolutions - 720p and 1080i. These are 16:9 ratios of horizontal to vertical. This means that if you take the vertical resolution, divide by 9, then multiply by 16, you get the horizontal resolution in pixels. The 720p resolution is 1280 pixels wide, while the 1080i resolution is 1920 pixels wide. This is good to know if you want to hook a computer up to a standard HDMI monitor, where you will want to select the proper resolution on the computer to match the monitor, either 1280x720 or 1920x1080.

The "i" and "p" letter suffixes to each resolution indicate whether the screen is "interlaced" or "progressive" scanned. With an interlaced scan, the video image is drawn on the screen in alternating lines. So, lines 1, 3, 5, 7, etc. are first drawn. Then, when the last available line is displayed, the rest of the lines are filled in (2, 4, 6, 8, etc.). The resulting image is usually good enough for most material, but with faster moving material, it can produce some "flickering", where the individual lines can be perceived.

On the other hand, a progressive scanned image is drawn sequentially, line by line. This produces a cleaner image, without the flickering that can sometimes be caused by interlacing, but requires that the image be drawn at twice the speed of an interlaced image. This means that the equipment must be capable of transferring twice as much material in the same time as that of an interlaced image. To put it in technical terms, it needs to be able to handle twice the "bandwidth", which is the amount of data that can be transferred each second.

Under the requirements for High Speed HDMI falls the more advanced resolutions, which are 1080p and 4K. From the above, you probably already see the 1080p as being a progressively scanned image with 1080 lines of resolution and 1920 pixels wide.

On the other hand, 4K is not as intuitive, but it makes sense once you know what it means. The 4K resolution has the same number of lines tall and pixels wide as you would have by placing four monitors together, two wide and two tall. So the 4K resolution is 1920 x 2 = 3840 pixels wide and 1080 x 2 = 2160 lines tall. The 4K resolution is not commonly found yet, except in the more advanced cinematic displays and source devices. However, with the larger size displays starting to appear on the market, the 4K resolution will soon be introduced into the mainstream consumer market.

Another High Speed HDMI video feature is 3D support, which is becoming more commonplace with the recent trend towards 3D movies at the theater and 3D support in video game consoles. Processing 3D signals requires more bandwidth, but in general, if a device has the bandwidth for full 1080p and 4K resolutions, it should also be able to pass 3D video signals.

Understanding HDMI® Video - Color Depth

In addition to the basic consideration of video resolution, another important factor in video displays is the number of colors that can be shown. The world around us has an infinite number of different color shades, while video equipment is necessarily limited in the number of colors that can be displayed, which is known as Color Depth. Color Depth is a measurement of the number of bits of data that can be assigned to produce different color shades - the more bits, the more colors that can be displayed.

For HDMI the Color Depth is usually measured as the number of shades of color intensity assigned to each of the primary color channels: red, green, and blue. The basic requirement is that each channel be capable of handling 8-bits of color intensity for a total of 24-bits of information for each picture element (aka pixel, or each dot on the screen). A 24-bit Color Depth equates to over 16 million different colors, which produces vivid, lifelike color images.

More advanced Color Depths use more bits per channel, including 12-bits per channel (36-bits total) for over 68 billion colors and 16-bits per channel (48-bits total) for over 280 billion colors! Among these are various "Color Spaces", which are predefined sets of colors, which include x.v.Color™. x.v.Color is a promotion name given to the products that have the capability to realize a wide color space based on the xvYCC specifications and is a trademark of Sony Corporation. Currently only AVCHD™ camcorders and PlayStation 3 consoles support the x.v.Color color space.

Understanding HDMI® Audio

Compared to video signals, audio signals require significantly less bandwidth, even for the highest quality. This means that all HDMI equipment can handle high-quality audio signals, including uncompressed 2-channel PCM with sample sizes up to 24-bits and a 192 KHz sampling rate. It can also support compressed 5.1 and 7.1 channel audio.

More advanced audio types are also supported, but these require a bit more bandwidth. These include Dolby TrueHD™ and DTS-HD Master Audio™. However, even Standard HDMI Cables have sufficient bandwidth to carry these audio signals, along with the basic HDMI video resolutions (720p/1080i).

One more audio consideration is the Audio Return Channel feature in the HDMI specification. The Audio Return Channel is a way to carry audio signals back down the wire. This is most commonly used when you have an HDTV using its internal tuner (i.e., not getting its signal from an external source device). In this case, if you want the audio to play over your surround sound speaker system, you will need a way to carry the audio signal from your TV to the receiver/amplifier.

The Audio Return Channel is the part of the HDMI specification that accomplishes this. However, while all HDMI cables can carry the Audio Return Channel, only equipment that is specifically designed to process and/or transfer the Audio Return Channel can take advantage of this feature. If the feature set for a piece of equipment does not specifically list support for the Audio Return Channel, then it does not include Audio Return Channel support.

Understanding The HDMI® Ethernet Channel

One more major HDMI feature that bears mention is the HDMI Ethernet Channel. The HDMI Ethernet Channel is a method by which internet connectivity can be shared between properly equipped devices, without the use of additional wires. For example, if your blu-ray player is connected to the internet, your television can also be connected through an HDMI Cable With Ethernet.

As with the Audio Return Channel, all the equipment and devices must specifically be designed to process the HDMI Ethernet Channel. Unlike the Audio Return Channel, normal Standard and High Speed HDMI Cables are not capable of carrying the Ethernet signal - you must use Standard or High Speed HDMI Cables With Ethernet.

With many devices now equipped with wireless network adapters, the usefulness of the HDMI Ethernet Channel is somewhat diminished. However, a wired Ethernet connection can produce greater speeds and throughput, so the HDMI Ethernet Channel is worth using if your equipment supports it.

Understanding HDMI® - Hz, MHz, and Gbps

First, what do they mean?

Hz is short for Hertz, which means "cycles per second".

MHz is short for Megahertz. 1 MHz is 1 million cycles per second.

Gbps is short for Gigabits per second. 1 Gbps is 1 billion bits per second.

So, how do they relate? Without getting too deep into the technical aspects, when you see an HDMI number with Hz next to it, it is usually something like 24, 60, 120, or 240 Hz. This is referring to the refresh rate, which is the number of times each second that the screen is drawn, also known as the number of frames per second. The common television refresh rate before HDMI came along was 29.97 frames per second for NTSC and 25 frames per second for PAL.

With HDMI the Hz rating can vary from 24 to 60 Hz for a normal 1080p display. Televisions may refresh their screen more often, which means that they end up redrawing the same frame of video signal several times. A television with a 240 Hz refresh rate will redraw each HDMI 1080p@60Hz frame four times.

The MHz and Gbps numbers are closely related. They refer to the clock rate (MHz) and the associated bandwidth (Gbps) of the HDMI signal. A 165 MHz clock rate equates to a bandwidth of 1.65 Gbps. The two terms are generally interchangeable when discussing the video amplifier and how much data it can handle in any given second of time. The minimum clock rate/bandwidth required to transmit a 1080p@60Hz signal with 8-bit per channel color depth is 165 MHz/1.65 Gbps per channel, or 495 MHz/4.95 Gbps total.

The most important thing to remember about all this is that a higher Hz rating means a clearer signal with less flicker, while a higher MHz/Gbps rating means that more information can be transmitted and processed each second. More data means more features - higher resolutions, Deep Color with higher bitrates, 3D video signals, and higher quality multichannel audio.

HDMI® Devices - What To Look For?

When shopping for HDMI devices, whether they are source devices (e.g., blu-ray players), sink/display devices (e.g., televisions), or repeater devices (e.g., switches or splitters), you should look for specific support for the features that are important to you. If you do not need 4K or HDMI Ethernet Channel support, there is no need to spend money on equipment or cables that include those features.

For "repeater" class devices (e.g., switches, splitters, and extenders), another primary consideration is the video amplifier bandwidth. There are a couple of important numbers to keep in mind when looking at these devices:

2.25 Gbps - The minimum bandwidth required to transmit a 720p/1080i signal at 60Hz with 8-bit per channel color depth is 0.75 Gbps per channel, or 2.25 Gbps total.

4.95 Gbps - The minimum bandwidth required to transmit a 1080p signal at 60Hz with 8-bit per channel color depth is 1.65 Gbps per channel, or 4.95 Gbps total.

6.75 Gbps - The minimum bandwidth required to process a Full High Definition 3D signal (1920x1080 resolution for each eye at 24 Hz refresh rate) is 2.25 Gbps per channel, or 6.75 Gbps total.

10.2 Gbps - The current minimum bandwidth requirement of the High Speed HDMI standard is 3.4 Gbps per channel, or 10.2 Gbps total.

HDMI® Cables - Basic Choices

With HDMI Cables things are much simpler. For home theater applications, there are two choices with a single option for each. The two choices are:

High Speed HDMI Cable - This is a cable designed to handle 1080p and 4K resolutions. It is required to have a bandwidth of at least 10.2 Gbps, which is enough to process all but one of the features in HDMI at the same time, including 3D, 48-bit Deep Color, Audio Return Channel, and any type HDMI supported audio signal. The one feature it cannot handle is the HDMI Ethernet Channel.

Standard HDMI Cable - This is a cable designed to handle 720p/1080i resolutions and capable of a total minimum bandwidth of 2.25 Gbps. Standard HDMI Cables can handle some of the HDMI features, but not all at the same time like a High Speed HDMI Cable can. The one feature it cannot support is the HDMI Ethernet Channel.

As you probably guessed by now, the one option for each of these cable types is the addition of support for the HDMI Ethernet Channel:

High Speed HDMI Cable With Ethernet - This cable can do everything that a High Speed HDMI Cable can do, with the addition of support for the HDMI Ethernet Channel.

Standard HDMI Cable With Ethernet - This cable can do everything that a Standard HDMI Cable can do, with the addition of support for the HDMI Ethernet Channel.

There is a fifth cable type, which is the Standard Automotive HDMI Cable, but that doesn't apply to home theater applications. If you've got a car HDMI installation, you will use this cable and won't have any other choices to make.

In general, if you are hooking up a 1080p 3D ready blu-ray player to your 1080p 3D ready TV, you will want a High Speed HDMI Cable. If you've got a TV that is only capable of 720p and you won't be using 3D, you will want a Standard HDMI Cable.

However, it can get a bit more complicated...

HDMI® Cables - AWG Explained

A cursory examination of the Monoprice HDMI Cables pages will reveal that there are more choices than just Standard and High Speed. What is likely to jump out at you are the different AWG (American Wire Gauge) ratings of the different cables. There are 28 AWG High Speed HDMI Cables and 22 AWG Standard HDMI Cables. What does all this mean?

First, AWG (American Wire Gauge) is a measure of the thickness, or gauge, of a wire. The system is based on the number of times a wire could be wound around a spool of a given width, so a 30 AWG wire could be wound 30 times, while a 20 AWG wire could handle only 20 windings. Therefore a 20 AWG wire is thicker, with a larger diameter, than a 30 AWG wire.

Wire gauge directly relates to the amount of electrical current that can be carried on the wire. The larger diameter of wire, the more current it can carry. In terms of HDMI this means that a larger gauge wire (smaller AWG number) is capable of higher bandwidth than a smaller gauge (larger AWG number). Therefore, a 22 AWG wire is capable of higher bandwidth than a 28 AWG wire.

If you look closely at the HDMI Cables pages, you will see that there are cutoff points for High Speed HDMI Cables in each AWG grouping. Beyond the cutoff the cables of the same AWG are rated as Standard HDMI Cables. The longer cables are not made any differently, however. As the length of a wire increases, so does the overall resistance of the wire. Increased resistance means decreased current capacity and therefore decreased bandwidth in HDMI terms.

The cutoff points for High Speed HDMI Cables of each AWG rating are:

28 AWG = maximum 10 feet

26 AWG = maximum 12 feet

24 AWG = maximum 15 feet

22 AWG = maximum 25 feet

So a 12 foot 28 AWG HDMI Cable is not rated for the full 10.2 Gbps required for the High Speed designation. However, it doesn't just jump down to the minimum 2.25 Gbps required for Standard HDMI Cables. It may be capable of 9.5 Gbps, which is almost enough for the High Speed rating, but because it isn't 10.2 Gbps, it must therefore be classified as a Standard HDMI Cable. The longer the wire, the lower the bandwidth it will be able to handle. However, all of our HDMI Cables are capable of at least the 2.25 Gbps minimum required for Standard HDMI Cables.

HDMI® Cables - More Considerations

There are a couple more considerations when choosing an HDMI Cable.

First is the application. If you are connecting a cable directly from the source (blu-ray) to the sink/display (TV), you can be assured that if the cable is rated for High Speed, you can get the full 10.2 Gbps, especially if your length is less than the cutoff length.

However, if you are installing a repeater device, such as an AV receiver, an HDMI switch or splitter, or anything else in between, you should consider that each connection adds some amount of resistance to the total connection. So, even if your total length is less than 10 feet, you may have too much total resistance for a set of 28 AWG cables to handle High Speed signals.

For this reason, Monoprice always recommends the use of minimum 24 AWG cables when connecting any intermediate device between the source and the sink/display. It may even be advisable to go with 22 AWG cables, just to be safe.

Another consideration is the Silver Plated option found on some of the HDMI Cables we offer. HDMI signals are at such high frequencies that the signal itself rarely penetrates to the core of a wire. Instead it rides along the outside of the cable in what is known as the "skin effect".

Silver is a better conductor than copper (it has lower resistance, so can handle higher bandwidths), but is too expensive to make solid wires from. However, plating a wire in silver is much cheaper and takes advantage of the skin effect. Since the signal is only riding along the outside of the wire anyways, the silver plating gives the signal a lower-resistance path, which increases the bandwidth capability of a cable. If a normal cable is on the edge of being able to reliably handle the full 10.2 Gbps bandwidth required for High Speed, the silver plating can make the difference between a reliable signal and one which occasionally cuts out or that produces digital artifacts.

HDMI® Cables - Introducing RedMere®

RedMere® cables have been recently introduced to the Monoprice catalog of HDMI Cables. RedMere cables have a small chip in the HDMI connector, which boosts the performance of the cable. The significant factor about RedMere cables is that they break the rules above about cable gauge (AWG) and maximum lengths. RedMere cables can be much thinner than normal HDMI Cables and can reliably handle High Speed (10.2 Gbps) signals to much greater lengths. HDMI Cables with RedMere chips can handle full High Speed 10.2 Gbps signals to a maximum of 20 meters (65 feet)!

RedMere cables cost a bit more than normal HDMI Cables, but the greater length for High Speed signals, combined with the overall thinner cables (which are easier to manage) more than make up for the slight additional cost. One important point though is that RedMere cables are directional. While you can hook either end of a normal HDMI Cable to the source and sink/display devices, you must connect RedMere cables in the proper direction.

HDMI® Cables - Does Higher Price Mean Higher Quality?

In many things you do get what you pay for, but not when it comes to HDMI cables. Don't take our word for it, however. The editors of CNET, one of the internet's most respected reviewers of consumer electronics, wrote an article about HDMI and included a section titled "What HDMI Cable Should I Buy?".

Some notable excerpts from the article:

If you walk into your typical electronics store to buy an HDMI cable, you're likely to see prices upward of $50 with promises of better performance and faster speeds. Do you really need to spend that much money on a single HDMI cable? Absolutely not--those cables are a rip-off. You should never pay more than $10 for a standard six-foot HDMI cable. And despite what salesmen and manufacturers might tell you, there's no meaningful difference between the $10 cable and the $50 cable.

The editors at CNET are so confident that cheap HDMI cables offer identical performance, we've been using inexpensive Monoprice HDMI cables in the CNET Home Theater Lab for more than a year with no issues. That's saying a lot, especially when you consider that our video experts are constantly swapping in new products and changing configurations, which means our cables take much more abuse than they would in a normal home theater. We're also accustomed to making long cable runs, and many of our cables from Monoprice are 15 feet long. We also use even longer 20-foot cables from a generic maker with no appreciable loss in video quality. If cheap HDMI cables are good enough for the eagle-eyed video professionals at CNET, we're betting they're good enough for your home theater.

Recently Mario Armstrong discussed the best way to stretch holiday entertainment dollars on The Today Show (click this link to see the video). At about 2:26 in the video he mentions that HDMI cables are "way overpriced in the actual big box retailer stores" and that it is best to get your HDMI cables online from internet retailers, such as Monoprice.

If you are still a bit skeptical, look around the internet at various forums, such as on AVS forum to see what other consumers are saying. You will find an almost 100% consensus that inexpensive HDMI cables perform just as well as cables costing 10x or even 100x the price. You will also find that, more often than not, Monoprice is mentioned as the best place to get your HDMI cables.

Finally, it is important to remember that all Monoprice cables carry a full lifetime guarantee. If it ever goes bad, we will replace it with a new cable at no charge. Additionally, we offer a 30-day satisfaction guarantee. If you try it and don't like it, you can return it for a full refund!

Conclusion

While the technical aspects of HDMI can be a bit confusing, we hope that this guide has helped make some sense of what is most important when shopping for HDMI equipment and accessories. If there is something that you are still unsure about, please feel free to contact our Technical Support representatives via email or our Live Chat interface. They will be happy to answer any questions you might have and help you choose the right equipment for your needs. Most importantly, they can help you get the most value and usefulness from your limited entertainment dollars!

HDMI, the HDMI Logo, and High-Definition Multimedia Interface are trademarks or registered trademarks of HDMI Licensing LLC in the United States and other countries.

x.v.Color is a trademark of Sony Corporation.

AVCHD and the AVCHD logo are trademarks of Panasonic Corporation and Sony Corporation.

PlayStation and PlayStation 3 are trademarks or registered trademarks of Sony Corporation.

DTS is a registered trademark and the DTS logos, Symbol, DTS-HD and DTS-HD Master Audio are trademarks of DTS, Inc.

Dolby and the double-D symbol are registered trademarks of Dolby Laboratories.

RedMere is a registered trademark of Redmere Technology, Ltd.