Setting up a realtime physically distant rehearsal

Introduction and Videos:

I recently recorded several videos to demonstrate the use of standard live audio equipment to hold realtime rehearsals while maintaining appropriate physical distance. I used slight variations on the technology each time. Each of these experiments used cars as a means of providing each singer a personal protected space in which to sing, which also protected people around them.

Here is our preliminary list of procedures and safety precautions.

For the first experiment, I used equipment I had on hand for a hastily assembled “rehearsal.” Four singers arrived in three cars, and I gave each of them a wireless microphone. I ran the output from the wireless mic receiver into my mixing board, and then sent the sound back to the singers through an amplified speaker. It wasn’t ideal, but it did allow us to have a coordinated, safe, rehearsal process.

For the second experiment, I bought an FCC approved FM wireless transmitter for $8 at Walmart. I replicated the previous setup, but plugged the FM transmitter into the headphone jack of the mixer. With my wife in another car, we demonstrated that this provided a near zero latency rehearsal experience even for distantly spaced people, and took advantage of the fact that most personal vehicles already have an FM radio to receive the signal, thus creating an in-car monitor where singers can hear each other.

Since both of these videos were just intended to test and prove the technological limits and capabilities, I proceeded to record a Lassus trio with two friends with the goal of actually rehearsing a sophisticated piece of music. This short piece shows what the experience was like for me.

UPDATE: Here is another video of a collaboration with Bradley Lehman, in which he played harpsichord from a room in his house, while I sang in my car.

UPDATE 2: Here is video of a Harmonia Sacra sing, with 10 participants. I was an 11th participant when I wasn’t filming.

Update 3: Here is video of the 8 voice Cantore singing a men’s arrangement of Bruckner’s “Locus Iste”

Update #3.5: Bryce Denney and Kathryn Troup Denney independently came up with this system for a driveway choir using gaming headsets:

Update #4: Here is a video that demonstrates the need for equipment even in a hall, if performers are kept distant. The edited video with the sound from the board will be broadcast Friday as part of the Shenandoah Valley Bach Festival’s virtual concerts.

Update #5: Here is the edited video from the session seen in update #4. The sound is essentially what we heard in our headphones. The solution to distancing this time used my good recording mics (AKG C-414) and long XLR cables. The FM Transmitter and an old FM stereo was still the most convenient way to get sound to David Berry’s headphones.:

Update #6: I was invited to sit in on the Good Company’s first attempt to rehearse using this technology. None of the equipment was mine. (There is a list of equipment used at the end of the video.) We did also learn in this rehearsal that there are some modern car stereos that do some kind of digitization of radio signals, introducing unexpected latency. Fortunately, a portable radio was on hand to provide sound to that car!

Update #7: on Friday, June 12, I met with Jared Stutzman and the Concert Choir of Eastern Mennonite High School. We used a combination of equipment from his school, supplemented by my own, to host a rehearsal for 13 students in 12 cars. I took a lot of video, but I wasn’t able to record audio from the board. I’ll still try to put together some video footage. We’re planning to do this again with an even larger choir now that I’ve acquired more microphones.

Update #8: I’m behind in video editing, but I facilitated a volunteer Hymn Sing on Saturday, June 21, with 16 participants, all on wireless microphones. It definitely worked, though we encountered new issues to confront. There was some initial problem setting levels and some issues with distortion that were hard to diagnose. However, I learned more about the importance of antenna placement, and learned in a private session on Sunday that the batteries were low in the FM transmitter, which truncated its already limited range.

Lessons Learned:

The most important lesson is that this can work to allow people to sing together safely. It is not the only answer, but it is one possible solution to allow people to safely sing together in realtime.

There are many variations on the setup that could be used to accommodate different populations, different size groups, and different risk profiles.

All of those choices involve various tradeoffs.

Sound travels at about 1 foot per millisecond. Light and radio waves travel closer to 180 miles per millisecond, depending on the medium through which they travel. Chamber ensembles are used to dealing with latencies (from the speed of sound) of up to 20 milliseconds or more, due to the physical space between participants. Larger groups may routinely experience latencies as large as the stages they inhabit, and these often become problematic. These problems are amplified in a virtual ensemble.

Using standard audio equipment can cut down on the travel time of audio information by converting it to a form that travels at light speed and then back to sound, with minimal time delay for the conversion.

The same is true for Internet audio communications, but they are saddled with the additional latencies of converting analog signals to digital packets and handling the reassembly and conversion of those digital packets back into analog signals. Progress has been made on streamlining that process, but live audio equipment can bypass those latency-inducing tasks.

Each component of a live audio system can be obtained at various price points, with varying levels of impact on the quality of the system.

In our attempts to rehearse using this system, we did not have someone monitoring the mixing board. We all agreed that results would be better with someone monitoring the board, and it would be ideal to have a dedicated live sound engineer.

In addition, many live sound engineers are probably out of work or underemployed right now. It would be wise, if trying to provide a rehearsal opportunity like this, to work with a local professional both to run sound and to recommend and assemble equipment.

If a group sings with microphones, they will need to invest time in learning how to use them well.

Surprisingly, there were no problems with feedback in our vehicles with any of the microphones used.

It is possible to mix wired and wireless microphones, given enough mixer capacity, which may offer a way to avoid frequency crowding with larger groups.

It is helpful to have compression on your mixing board.

Some newer cars have digital audio systems that introduce delay. It is wise to have boomboxes or other alternatives to provide to any affected parties.

Wireless microphone receivers should have their antennae set at right angles to each other in order to ensure consistent reception of the signal, and should maximize sightlines to the microphones. Large setups may need additional reception aids, like an antenna distributor and RF analysis tools.

Fresh batteries should be put in the FM transmitter and all microphones on a regular basis, well before they lose power.

Equipment list:

There are many variations, but I’ll try to address the individual components. Any advice I offer should be taken with the understanding that I’m not an expert in audio devices, and there are many ways one can balance the desire for quality versus cost.

After talking with Tom Carr, one of the most sophisticated audio pros I know, I think we agreed that for this sort of work, it is important to keep costs low and equipment management on the simple end. Large groups are hypothetically manageable, but will require much more significant effort than a small group.

This is the equipment I used:

GTD Wireless Mic System ($288)

Behringer Mixer ($299)

FM Transmitter ($8) from Walmart

XLR cables to connect wireless receiver to the mixer (though a 1/4-inch cable would work if you used the mixed output.) and a 1/8-inch-to-1/4-inch adapter to plug the transmitter into the headphone jack.

1 multi-outlet 25-foot extension cord.

1 rack mount I bought used for $75. (Next time, I’d just build one for cheap.)

Cars with FM radios.

Because there is a mixed output from this wireless four pack, if you only had four or fewer people, you don’t necessarily need a mixer. Just take the mixed output from the receiver, use a home stereo to amplify the line level output to headphone level, and plug the fm transmitter into that. A mixer would only be needed for a larger group.

Mine is, in some ways, an excessive system for the number of people I’ve tested with so far. The mixer can combine the output from 12, 4-channel wireless mic packs, so could effectively handle 48 inputs if there were enough room in the frequency spectrum to handle all those mics. I will be doing more experiments soon with more voices, as I’m able to coordinate people and equipment.

On the other hand, if I add any more mic packs, I will probably want a bigger mixer that has compression on more channels.

Variations:

You could run sound back to people in a variety of other ways. In the first video, I amplified the sound through a single powered speaker. That is simpler in some ways, but adds a time delay for the sound to reach singers ears, and would be unclear unless windows were open, causing some additional contagion risk. I’d find the latency, though, to be a bigger issue. You could run multiple speakers out among the cars, minimizing the time delay, but you still have the problems of open windows.

You could run headphones to each individual. If I did this, I’d ask each individual to bring their own headphones, so they wouldn’t need to be decontaminated each time. This is less simple than transmitting the audio over FM wavelengths, and probably less consistent.

You could use regular wired microphones instead of, or in addition to wireless ones. You’d need a large enough mixer to accommodate them. This would bring the cost per person down slightly, and avoid the problems of frequency crowding. XLR cables can be bought in bulk for $15 – $25 apiece depending on length, and decent cheap xlr dynamic microphones can be bought for another $20 apiece. People would need to leave their windows open far enough to accommodate the cords. The drawbacks of this are mostly the time it would take to run all the cords, the slightly additional contact involved, and the more intense mixer needs. However, this might make it more reasonable to have choir members keep their own microphone, avoiding the need to disinfect them after each use.

Colleagues have suggested to me that they’ve thought of using technology in similar ways with physical distance in a classroom or large venue (which seems very risky to me) or in an open air space (which still seems somewhat risky, but less so.) I haven’t heard a solution that sounds as safe as people remaining in their own vehicles, though that is certainly unworkable for groups below driving age, or who don’t all have access to a vehicle. If someone were able to engineer separate, ventilated, disinfectable sound booths, that could approach the safety of personal vehicles, and could be hardwired for sound.

I am sure there are more variations I haven’t thought of. I hope other people will lend their own brainpower to finding other solutions to allow people to continue to make music together.