Some video switchers have built-in scan converters for converting VGA signals to an internal standard that you can use in your live production workflow. If you don’t have that, then you’re going to need a converter like the Grass Valley ADVC-G1 that can convert that VGA to your output. In this tutorial we’ll explore how the ADVC-G1 works and how you can incorporate it into your workflow.
Grass Valley markets the ADVC-G1 converter as an any-source-to-3G SDI converter, but specifically they mean it’s an HDMI input, DVI-I input, and analog video input converter. The “I” in DVI-I stands for integrated, and includes both analog and digital and both single- and dual-link DVI standards.
Digital and Analog Inputs
The DVI digital side isn’t too terribly exciting. It’s very similar to HDMI, but for me the exciting part is the A side, the analog side, because it can be converted from a VGA input using a very simple adapter, like the one shown in Figure 1 (below), which has DVI on one side and VGA on the other side. These are very inexpensive adapters of the sort that ship with video cards and what not–most likely, you already have a few sitting around your studio.
Figure 1. A typical VGA-to-DVI adapter.
It might sound a little bit strange to be describing VGA as “exciting” in 2014, but unfortunately, when it comes to IMAG and powering projectors, a lot of the presentation world still runs on the VGA standard for a variety of reasons. If you’re doing live switching and incorporating computer inputs, you need to be prepared to work with the VGA standard and convert it to a digital standard that our video switchers can handle.
Some video switchers have built-in scan converters, which is what’s required to convert VGA to an internal standard that you can work with. If you don’t have that then you’re going to need a converter like the Grass Valley ADVC-G1 (Figure 2, below) that can convert that VGA to your required output. In this case, that means SDI, but there are also converters that can do HDMI, and those are really the two digital standards that video switchers are built around.
Figure 2. The Grass Valley ADVC-G1. Click the image to see it at full size.
On the audio side you can work with the embedded HDMI audio as well as a 1/4″ TRS analog input or AES or EBU digital audio inputs, which you can embed into the HD-SDI output.
On the output side (see Figure 2), the ADVC-G1 supports two 3G HD-SDI outputs. The 3G HD-SDI standard simply means that it supports resolutions of up to 1920×1080 at 60 progressive frames per second (fps). The 1.5G standard does not support those progressive frames, maxing out at 60i.
Signal Processing Options
There are a few different signal processing options available. One of the more interesting options is 3D NR–3D noise reduction–which is really useful when you’re working with compressed codecs, generally on playback from a non-live source. If your source camera is a small sensor-type camera–using a 1/3″ or 1/2.8″ sensor–or if you’re working in high-gain or high-ISO environments, or even when you’re upconverting from an analog source to digital or to a larger frame size, all of those scenarios can produce a little bit or a lot of noise when you’re upconverting and processing. Using a bit of noise reduction really goes a long way, and it’s especially important when you’re webcasting, especially because you’re using a very small bitrate and high compression ratio. Noise detracts from the detail in your video, so the higher signal-to-noise ratio, the better your finished video will look.
Figure 3. The bottom panel of the ADC-G1 shows image-processing and enhancement options. Click the image to see it at full size.
The second image-processing feature is Image Enhance, which enhances detail by increasing the sharpness. You wouldn’t want to use that feature if you were working with a noisy signal, but if you already have a very clean signal to begin with that’s noise-free, you may want to add some sharpness to your image.
Framerate Conversion and Pass-Through
There are two things you might be looking for in a converter that the Grass Valley ADVC-G1 doesn’t do. The first is framerate conversion. If your input source is 1920×1080 30p, you can’t output 60i or 60p as a framerate, same as if you have a 60p or a 60i input you can’t output 30p.
It’s also worth noting that the ADVC-G1 does not support pass-throughs, so if you have a HDMI, a VGA, or any of the analog video inputs, you can’t output the same input as a pass-through. The only outputs are HD-SDI.
These aren’t big limitations, but you just have to be aware that these are in place.
The Grass Valley ADVC-G1 converter has a variety of different inputs on the front of the unit (as shown in Figure 2), and the active input selection is made from the back.
There are dials and DIP switches to control the settings, but the active setting on the front is indicated by an LED light (Figure 4, below).
Figure 4. The LED light indicates the active setting.
There’s also a light for the upconversion, as shown in Figure 4 (above). There are video input lights and audio input lights that indicate whether the signal is stable, selected but not active yet, and if the upconversion is turned on.
ADVC-G1 Rear of Unit
On the back of the converter Figure 5 (below), there are three things I’d like to highlight. The first is the locking mechanism on the power adapter plug (on the left in Figure 5). You can’t unintentionally pull it out, but if you retract the sheath, it pulls out fairly easily.
Figure 5. The rear of the ADVC-G1 features the power plug, audio and video select buttons, and DIP switches. Click the image to see it at full size.
Also found on the back of the unit are the audio and video select buttons (center, Figure 5, above). These are dials that need to be manually turned using a precision screwdriver, and the reason they are here is because the unit does not have an auto-detect or select feature, and there’s no external buttons to toggle between the available inputs. The cheat code for the inputs is on the bottom of the unit (Figure 3). This walks you through which inputs are available and which number they correspond to.
Finally, the back of the unt also houses the selections for the DIP switches (on the right in Figure 5, above). The DIP switches allow you to switch signal processing. So whether it’s the output resolution you wanted to adjust or the signal processing like image enhancing or noise reduction, those are controlled on the back of the unit.
The last thing I want to do in this tutorial on the Grass Valley ADVC-G1 converter is to walk you through a VGA conversion. (You can watch the process step by step from the 6:53 mark in the tutorial video below.)
In the setup for this tutorial, the VGA output from my laptop is going into the converter using a simple VGA-to-DVI converter. The output is HD-SDI, and that’s going into my recorder and monitor. And, as you can see in Figure 6 (below), there’s a valid and high-definition digital output that’s coming out of there, so that conversion is complete.
Figure 6. My VGA conversion setup. Click the image to see it at full size.
At this point, I do want to point out a few caveats and warnings. It’s important in a video workflow to consider all of the video resolutions that you’re going to be given and working with, and to make sure that they’re compatible with your hardware. This applies to any workflow that incorporates the ADVC-G1 converter. It does support a wide range of video resolutions, but there are some video resolutions that you might be given that aren’t specifically supported.
On the HDMI and the DVI-D side, it should be able to handle pretty much everything that you’ll be given, because in most cases you’re going to be working with digital HD video inputs like 1920×1080 or 1280×720.
But when it comes to the DVI-A standard–otherwise convertible to VGA–there are a variety of resolutions that you might be given from computers that are not supported. Of the supported DVI-A video resolutions there’s only one that’s widescreen, and that’s 1360×768. That’s a proper widescreen video resolution. Unfortunately it’s not the default resolution that you’ll find that most video cards output, including the laptop I’m using in this tutorial, which natively supports 1366×768, rather than 1360×768. That’s only a six-pixel difference, but when it comes to conversion and standards compliance, if it’s the wrong resolution it just won’t work in the workflow. So you’ve got to make sure that you’re able to output a 1360×768 video resolution if you want to maintain that widescreen aspect ratio from computer inputs.
Author’s note: When I pointed out my concerns to Grass Valley regarding the limited DVI-A support that did not include common widescreen resolutions, the rep I was working with informed me that Grass Valley is working on a feature update refresh that would add 1920×1080, 1280×720, and 1366×768 support for the DVI-A input.