Integrated Blogs: EDID: The Dark Art of AV Systems Made Easy

By Matthew Hale

Anyone designing, installing or commissioning integrated AV systems will be familiar with the term EDID. It stands for Extended Display Identification Data. I work in tech support, and a lot of my support calls are to assist engineers with configuring EDIDs. The fault reports can vary from slow switching speed, flickering displays, loss of audio or video. All of these can be caused or influenced by EDID configuration. But what exactly is it? How does it work and why is it important? There are myriad articles online and numerous training courses that go into great detail on what EDID does, but my aim here is to simplify the process by providing you with the fundamentals, and a few tips & tricks to get your AV systems switching as fast as they can and always provide the correct signal for your displays.

The first thing you need to know is that EDID is backwards. What I mean by that is, EDID is one of the very few signals that travels down a cable in the opposite direction to the video and audio data. EDID does not come from a source device. It comes from the sink device; the display. There are a few exceptions to this but I’ll explain later. The sink provides EDID down the signal chain to the source device, and the source device receives it.

You have probably noticed that in your display settings on your Windows laptop, the resolution is shown as “(Recommended)”. Why does it recommend a particular resolution? EDID, that’s why. The laptop has received an EDID through its video output, from the display. That EDID has all of the capabilities of the display in a coded format. It tells the computer what its native resolution is, and the computer sends its video signal with those settings. Even an integrated laptop display provides EDID to the computer.

EDID can provide a great deal more information than just the resolution. Frame rates, colour depth, HDR, 3D, audio encoding, manufacturer… The list is increasing every year. With all of that functionality comes complexity, which can be overwhelming. So here are some scenarios where EDID needs to be considered.

Designing

When considering EDID at the design stage, you only really need to consider the specification of the components and capabilities of cables. If you’re designing a 4K capable system, you will often start by specifying 4K displays and work back from there. It doesn’t matter if you’re using HDBaseT, HDMI, DisplayPort or a mix of those and other standards. EDID will inevitably flow down the chain to your source. However, it is important to consider whether a source device that is not capable of 4K will ever be connected to the system. If this is not accounted for at the design stage, the stability of the signals might be affected. For instance, if a 2K source receives an EDID with a native resolution of 4K but a capability for 1080p, it sends 1080p to the display. The display then has to scale up the image to fill the screen. This can introduce switching delays and signal latency. Third party hardware scalers are often far better, but they have to be configured correctly. I’ll get to that.

Installing

Key to good signal integrity is positive connections. Well terminated cables and good quality conductors are paramount. But there are other factors that can affect the integrity of EDID signals specifically. Some vendors specify very particular standards of Cat6 cables for HDBT signals. U/FTP, F/UTP, shielded, unshielded. They might even specify shield terminations to be soldered to the RJ45 connectors. The reasons for these particulars are nebulous and manufacturer dependent. The bottom line is that these specifications are set so that the system being installed can be given the best chance to meet the specification that the design demands. That includes EDID transmission. Always ensure that you meet the recommendations of the manufacturers, or troubleshooting EDID can be very time consuming.

Commissioning

The system has been installed. Everything is powered up. It’s now down to the commissioning engineer to make it all work. This is where a deeper understanding of EDID is necessary. It is at this stage when issues present themselves so it’s important to approach the issue with EDID in mind.

First let’s talk about switching speed. Switching between two source devices is slower than the manufacturer’s specifications. Why is this happening? It’s most likely to be EDID negotiation between the display and the source. It is most common when a display is reporting a native capability that the source device cannot match. For instance, a 4K capable display but a source device that’s only capable of 2K (1080p). If the native resolution of the display does not match the capability of the source device, it takes longer for the two devices to negotiate between them. We can rectify this.

Now let’s address the lack of audio. Audio is not being embedded into the HDMI stream. Why? This is most likely to be due to the EDID being sent by the display without any audio capabilities. Most often this is an artefact of using a projector with no speakers or audio output. These audio-less projectors provide an EDID without audio. This can cause audio de-embedding issues at all points of the signal chain due to the source device being told to not send audio as part of its video stream, due to the EDID received from the projector. We can rectify this.

Rectifying EDID Issues

There are tools and methods you can use to identify and rectify problems that you suspect are being caused by inadequate EDID config. The first and simplest one is to control the EDID somewhere in the signal chain, to omit the EDID from the display and replace it with one that has the specification you need. This is achieved with hardware EDID Minders or even EDID config tools inside your switching equipment. Most switchers and matrices these days have a web GUI and a page dedicated to EDID manipulation. This should be the first place you look. Does the EDID from the display have audio capability? What’s the resolution it’s asking for? Can your source device comply with the EDID that it’s receiving? You might even be able to lock an EDID to the specification that you require.

Another way of manipulating EDID is with a scaler. Scalers are designed to get around these signal incompatibility issues by receiving the EDID from the display for its own use, but assigning a completely different EDID to the inputs for the source devices. It then scales the signals received to match the capabilities of the display. This is perfect for those situations where a source resolution lower than 4K is required to be displayed on a 4K display without delays or flickering due to negotiation.

Here are some tools that you can use to identify EDID related issues.

EnTech Monitor Asset Manager: https://www.entechtaiwan.com/util/moninfo.shtm

This is a free Windows application that will deconstruct an EDID directly from the display that the PC is connected to. See exactly what the display is asking for. Save it as a .bin file.

Kramer EDID Designer https://www1.kramerav.com/gc/product/edid%20designer

This is another free Windows application that is specifically designed for Kramer products, but is a useful tool for other brands also. The .bin file you extracted from the EnTech application can be dropped into EDID Designer for editing and further analysis.

In summary, EDID is complex, but not difficult. There are tools and techniques that you can use to identify and rectify EDID related issues. The trick is to know when the issue you’re seeing is related to EDID. If it’s a resolution, frame rate, aspect ratio, slow switching, screen flickering or other issue as mentioned herein, you should start looking at EDID right away. It might save you a lot of time.