How to Master the Art of Digital Audio Mixing for Hybrid Events
Live-Stream Audio Considerations
Up until this point, I have only been focused on the audio for the venue. Now is the time to start considering audio for the live stream. If you are controlling the soundboard, you can utilize one of your soundboard outputs for your webcast audio. Normally, I prefer to have some control over the levels of each signal. In the venue, you have a much wider acceptable audio range than you do on a recording. The reason is that your PA speakers are much more powerful than laptop speakers, and venue show levels are generally louder than what a typical laptop can reproduce.
This gives you a much wider volume range before your audience struggles to hear what the presenter is saying. With audio on a webcast, you have to assume that the viewer’s ability to turn up their speakers is very limited, so if you want the viewer to be able to hear properly, your audio needs to be mixed within a much smaller range. Mackie had the right idea when it added a compressor to its V3 line, understanding that this was desirable for the growing field of digital content creators. However, for my workflows, I’ll take the graphic equalizer on the board, knowing I can add a compressor or a more advanced audio plugin later in my digital workflow.
I’m now going to cover three common options for getting analog soundboard audio into your live stream.
Music and movies benefit from stereo and surround-sound mixing, but most of the time, you’re going to send the same mono audio signal to both the left and right speakers when you are reinforcing microphone audio for conferences and keynote speeches. As a result, you might daisychain your signal from one speaker to the next, leaving you with a second, unused main output. Or, your soundboard could have a second set of main outputs, typically ¼" TRS outs, as opposed to the XLR mains.
If you are taking a main output signal, you need to realize that both your house and livestream signals are tied together. You then want to capture that audio in a device that gives you sufficient control over your audio levels for the webcast, which will change as you adjust the audio levels for the house. This might mean a second soundboard, but it could also include an external USB audio capture device, a video switcher, or even simply your video camera.
If you want to avoid having your audio tied to the house audio, you can use an Aux output. This could work for jobs with few audio sources, and it normally means if you need to adjust levels on an input, you would need to perform this task twice: once for the live stream and again for the house. Although, as I have mentioned before, since the house levels are more forgiving, you may not need to adjust them as often as you do for the live stream.
Some audio technicians are figuring out that if they set up their soundboards “backwards,” they have better control over the livestream levels and don’t impact the house levels. Instead of using the main outs for the PA speakers, they are using the mains for the livestream signal and are using the Aux for the house. The reasoning behind this is that the VU meters show the main levels, and having a visual representation of the levels for the livestream levels is important because the technicians can better monitor and adjust those levels with a calibrated meter. They don’t need a VU meter for the house levels because they are in the room and can adjust levels by what they are hearing.
If my soundboard is right next to my webcast laptop, then I typically will use the USB output on my analog or digital soundboards. On my Mackie analog board, the USB levels are tied to the input volume levels, not to the main volume levels, so I can still ride the input faders to adjust both mixes at the same time. I also still have the ability to adjust the signal to the loudspeakers with the main up or down.
I can’t always count on my soundboard being next to my laptop. One of the benefits of having a digital soundboard is that you can control it using a tablet, laptop, or control surface. For lectern microphones and panel discussions, I often use multiple wired gooseneck microphones. While I do have large audio snakes, or I could run multiple lines of XLR cable, it is a lot easier to use the soundboard as a stage box and have it closer to the microphones and their wired connections. I then can use Wi-Fi or run a single line of Ethernet back to my location and operate the controls using software or a control surface.
Secondary Audio Capture Devices
If you don’t have access to (or your main soundboard doesn’t have) a USB output, you have a few options for getting an XLR audio feed into your live stream. If you’re lucky enough to have a video switcher with XLR inputs and proper level controls, this might be the audio solution for you. The two switchers that I use for this are the Roland V-60HD and the Blackmagic Television Studio Pro 4K (Figure 5, below).
Figure 5. The Blackmagic Television Studio Pro 4K
By embedding your audio signal into your video program feed, you don’t need a dedicated audio capture device to capture audio into your live stream. Embedded audio will likely be the best workflow if you’re using a hardware encoding appliance like the AJA HELO or a Matrox Monarch.
I’m going to quickly mention that while you can also use your video camera’s XLR input as a way to embed the audio into your HDMI or HDSDI signal, I prefer that these controls and the responsibility to monitor and adjust these levels lie with my audio or webcast technician, not solely with my camera operator.
USB Audio Devices
If you’re using software like vMix or OBS to mix, record, and webcast, you will need a video capture card with embedded audio or a dedicated audio capture device if your audio has not yet been embedded. One common hardware device for capturing XLR audio to a connected webcast computer is the Behringer UMC line of USB audio interfaces. The line has models with one, two, and four XLR inputs, allowing you to mix multiple channels of audio in your webcast software.
Recently, I misplaced my Behringer UMC404HD, and when I was looking into replacing it with another one, I came across the Roland Rubix line (Figure 6, below). This line is more expensive than similar Behringer models, but I fell in love with some of the features and had to buy one. Ultimately, I found my UMC404HD. It was in the same properly labeled case where I left it, but once I found a better tool for the job, I just had to upgrade. Let me explain why.
Figure 6. The Roland Rubix44 USB audio interface
The Rubix line’s first standout feature is the green/red LED lights for each input and the output. These LEDs give a visual indicator that you have a signal and that it isn’t clipping. The second feature is the compressor/limiter control. On my Rubix44, which has four XLR/¼" combo inputs, there are two compressor/limiter controls—one for the first pair and another for the second pair. The front knob allows me to set the threshold. On the rear panel, there are three settings for this control that allow me to select two different compressor settings and one compressor with a limiter setting.
Having a hardware compressor and limiter for my soundboard feed means that I can get strong audio levels without the risk of clipping audio. Without a compressor and limiter, you have to be more cautious. But whereas broadcasters use -12dB for their average peak audio level, webcast producers need to be more aggressive, or their viewers on weaker devices will complain that it isn’t loud enough.
The third feature that the Roland Rubix has is a ground/lift switch. There is nothing worse than a ground loop hum entering your audio feed. This problem is easily and traditionally solved with a dedicated DI for each input, but having this function built into my audio capture device is one less piece of gear that I need to worry about and helps to justify the additional cost over the more popular Behringer UMC line.
Mixing audio for a panel discussion with multiple open microphones can get really tricky. Overall, there is too much room noise from all of the microphones, and you’re more prone to feedback. Mixing on an analog soundboard means you are likely riding the inputs constantly. Fortunately, there is a better way. My Behringer X18 digital mixer has an auto-mixer inspired by the patented work of Dan Dugan. (Fortunately for me but not for Dugan, his original patents have expired, and companies like Behringer, and even Roland on the V-60HD video switcher, are free to use this technology.)
Auto-mixing automatically gates each audio channel and activates only the ones being used. The attack speed to open the channel when someone speaks is faster than how quickly an operator can react and results in no detectible clipping. It is also able to determine which is the primary microphone. If the two microphones next to it are picking up weaker signals from the same speaker, it is smart enough to clamp them down too. The result is better, cleaner, and stress-free audio that is easy to implement.
Even if you have full control over the microphones, soundboard, and features like compressors and auto-mixing, you might still benefit from adding a few plugins into your workflow. But if you don’t have full control, these plugins can be a lifesaver. Here are a few of the Waves audio plugins that I purchased and use in vMix to improve my audio.
NS1 Noise Suppressor or WNS Noise Suppressor
Both of these are similar and are able to differentiate between vocals and noise and then allow you to eliminate the noise. Just be careful not to get too aggressive; this is because some noise sounds more natural than too clean of a signal, and going too far will result in an underwater sound.
This can be used in addition to or instead of a compressor/limiter. You set your desired levels, and the vocal rider automatically rides the volume to keep your audio levels more consistent. This is especially helpful when you have multiple audio sources to juggle. I tend to pair this plugin with a noise suppressor to avoid pumping the noise when someone isn’t speaking.
Video producers often overlook the importance of audio in their video productions, but it is a well-accepted fact that bad audio is worse than bad video. When managing hybrid events, you have to consider both the house audio and the live-stream audio with equal consideration. Regardless of whether your workflow uses an analog or digital soundboard, getting familiar with and using tools like the graphic equalizer and compressor/limiter and plugins like an automizer, vocal rider, and noise suppressor will help you deliver clean and strong audio to both your in-room and online audiences.
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