Design Requirements for Audio and Video Sources, Part One: Live-Capture Devices

Recently, I wrote about the AVL signal chain and how the audio, video and lighting systems are actually a single interconnected system, where audio, video and lighting signals go from source through processing and distribution to output. While there are many factors that affect the way this system comes together, the design considerations often start where the signal chain itself starts: the sources. In many cases, the source devices you select can drive the entire AVL system design.

Many design challenges can be created or solved simply by looking at the source devices involved in the system. Sometimes the selection of these devices is flexible and up to the system designer. Other times, the source devices are already chosen either by strategic customer needs or demands of the application itself. Either way, it is best to understand the types of source devices a system might encounter, so you can properly account for them and know how they will impact the system.

concert- singer 2There are many types of audio and video source devices in an AVL system, but they tend to fall into two broad categories. First, there are devices, such as microphones or cameras, that capture audio or video occurring within an environment. Second, there are devices that play audio and/or video. This can be playback of a recording, or it could be an electronically generated audio or video signal (such as a PC running PowerPoint). Given the inherent difference between capturing and playing, we’ll look at each group separately, starting with live-capture source devices in this post. In our next post, we’ll look at recordings and electronically generated audio and video, and address the considerations when these types of sources are used in a design.

Whenever you use a live-capture source device (such as a microphone or camera) in a room, it is generally for one of three reasons (or some combination thereof). First, you could be using it to ensure that everyone present in a large room sees and/or hears what is going at the center of focus (the stage, presenter, etc.). For audio, this application is called sound reinforcement, and for video, it is called image magnification (or IMAG). Another reason you could be using live capture sources is to allow people in some distant location to see and/or hear what is going on in the room. This could be web streaming, room overflow, web conferencing or even radio or TV broadcasting. Finally, you could be using live capture sources to record what is going on in the room, so others can see and/or hear what is going on in the room at a later time. Which purpose (or purposes) you have will affect what live-capture source devices you select.

Another major factor affecting live-capture source device selection is whether or not the source device is mobile—that is, if it will move or stay put. In some applications, such as meeting spaces or airports, the cameras and microphones tend to be permanently installed. This is because there tends to be one type of activity going on in the space, and the center of focus either doesn’t tend to change very much or covers the entire space. A different person may talk during a meeting or make an announcement on the airport PA system, but overall, the AVL system has a single, defined use at all times.

The goal for the AVL system designer in these cases is to place the microphones and cameras in locations that will capture all of the activity in the space. The system designer must have a strong understanding of the intended usage of the space, and place microphones and cameras in locations that will capture all of the desired activity. This may require omnidirectional microphones and wide-angle cameras to capture everything going on in the space, or it may require more directional cameras and cardioid microphones placed at specific locations, where the center of focus always tends to be. It could also have both. Meeting spaces tend to require even, whole-room coverage from microphones and cameras, as the action could come from anywhere in the space, and all activity is treated equally. An auditorium or lecture theater, on the other hand, might only have a microphone at the podium, as that is where the center of focus will be.

One caveat with installed microphones and cameras in meeting spaces is in regard to a trend called “bring your own device” (BYOD). As I said before, one of the reasons to have microphones and cameras installed in the room is to use them for web conferencing. As permanently installed videoconferencing codecs have given way to laptops using web-based conferencing tools like Skype, meeting room AVL systems need to be able to connect the camera and microphones to user-brought PCs. In these cases, USB output is needed from the source device—either using professional-grade web conferencing cameras or microphone mixers with built-in USB. Users can then bring their own laptops, connect via USB to the installed cameras and microphones, and have a web conference that includes everyone in the meeting space rather than only what can be seen and heard by the PC’s onboard camera and mic.

While they are very powerful when used correctly, fixed-installation microphones and cameras are only appropriate when there is a fixed point of action. In other applications, such as houses of worship or sports stadiums, where there is a presentation or event going on, the microphones and cameras are moveable. This is because the center of focus is constantly shifting. The focus in a church moves from worship singers to the pastor. The focus in a stadium shifts from team to team and player to player. At the same time, the action going on in the space is targeted—the audience doesn’t get equal weight of focus with the sports stars or pastors. The goal of the designer in this case is to have enough microphones and cameras to provide suitable coverage of the anticipated activity in the space, while giving them flexibility to move as the action changes.

This is one of the reasons that audio and video system designers struggle with “how much is enough” concerning microphones and cameras in these types of applications. The unknown can be quite a troubling variable. Do I need extra handheld microphones? What if there is an unexpected speaker? Do I need more camera angles? What if something is going on in a space my cameras can’t reach effectively? Experience within the space can help with addressing these challenges, but at the end of the day, the designer must find what they hope is an appropriate medium and move on to their next project.

It’s important to remember that the choice between fixed and moving is not an either/or selection. Even if most of the action is moving, there might be certain things that you will always want to capture, and the location of those things won’t shift. For example, in houses of worship, you might want room mics to capture audience reactions (something I’ve written about before), or you may always need a wide shot of the entire stage. In these cases, you could use fixed cameras or permanently installed boundary microphones for these applications, while also using moving mics and cameras for other parts of the system. Likewise, a lecture theater or boardroom might have permanently installed microphones, but also provide a lavalier or headset for presenters.

As you can see, there is a lot to consider regarding source devices, and we’ve only looked at microphones and cameras so far. In our next post, we’ll look at how PCs, media servers, CD players and other such sources affect the system design.

Have any tips for designing with cameras and microphones? Let us know in the comments.