AES Section Meeting Reports

Los Angeles - November 26, 2013

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On Tuesday, November 26 of last year, the Audio Engineering Society heard from Jenn Liang-Chaboud, West Coast Senior Market Development Specialist for Shure, on the past, present, and future of wireless live sound. Ms. Liang-Chaboud has a wide range of experience in live production sound, not only as having been a product manager for Shure, but working on the development of products from initial conception, working with high-end users to develop new ideas, to writing code, to user case studies after product release — and as a user, since she's a live performer and choreographer herself. She covered topics ranging from recent FCC policy and future developments, understanding what spectrum is available for live sound and how to get the most efficient use out of it, and how to engineer the most robust wireless transmission for the most demanding environments.
Ms. Liang-Chaboud began by talking about audio frequency coordination in a live-sound environment, and how the landscape is changing. Traditionally, she said, live production sound was able to take advantage of white space in the entire band from 470 to 806 MHz. This range of frequencies offers an ideal balance between antenna length requirements and the distance of transmission that's possible. In 2010, however, the use of wireless microphone transmitters in the upper part of this band, from 698 to 806 MHz, was made illegal by the FCC, as the bandwidth was auctioned off, and partially reserved for use in public safety. A good chunk of this auctioned spectrum was purchased by AT&T, Verizon and Qualcomm, for use in various broadband services. Although equipment purchased before June of 2010 may still work, that spectrum is no longer licensed for live-sound use and is subject to FCC fines, though as Ms. Liang-Chaboud notes: "Thus far I don't know of anybody who's gotten a fine, though I do know that Verizon has gone around and sent cease-and-desist letters to a few different people. The fine is actually rather large." Verizon first took advantage of their newly-purchased spectrum with the rollout of LTE and the release of the iPhone 5 in the last quarter of 2011; it was then that people who hadn't prepared for these changes really started to see their equipment not work.

What spectrum remained for use in production sound is between 470 and 698, in the so-called "white spaces" of the television spectrum. In 2008, the FCC defined new rules for so-called TV Band Devices (TVBD), which are unli-censed low-power devices limited to 1 W (4W EIRP). They are not allowed to operate below channel 21, or 512 MHz, so Ms. Liang-Chaboud suggests that wireless microphones that operate between 470 and 512 may be relatively un-impacted by upcoming changes in spectrum allocation. With respect to these new devices, operating between 512 and 698 MHz, they must follow these rules: Mode I devices are portable, but do not have geolocation nor access to an FCC-sanctioned database, and thus must operate at a lower power than Mode II portable devices, which must geolocate and access the databases at least once a day, to check for spectrum conflicts. A third class of fixed devices can operate at the highest power, but cannot physically move, and these are the only whitespace devices in current use. Providers such as Verizon have not yet released personal portable devices in this spectrum, although there has been some testing in Seattle and North Carolina.

Most of the whitespace bandwidth from Channels 21 through 51 is registered by licensed entities, which in-clude television stations, cable networks, and film and TV production. Unfortunately, theaters, hotels, convention centers, theme parks, churches, and schools are not technically eligible to obtain a license. To use whitespace spectrum, licensed entities just need to check in with the registration databases when they are in operation. For those of us in the unlicensed category, we must register 30 days in advance, and requests can be rejected by objections from licensed users. Obviously, knowing that you're going to need spectrum thirty days in advance can be a challenge in a fast-moving production environment. If, however, you are registered in the database, unlicensed users are required to avoid using your frequencies. The spectrum reference databases currently in operation are Spectrum Bridge, Google, and Telcordia, although a recent check of Telcordia seemed to show their database being down. For the production user, trying to obtain a license is a complicated process involving much paperwork and the expertise of lawyers.

What's coming up in the TV Band spectrum is an incentive auction. Unlike the sale of the 700 MHz band, which was wholesale and involuntary, the FCC is encouraging current license holders to make a decision whether to hold on to their current license, or to give up all or part of what they currently hold. By giving up their current allocation, they can move to a lower channel, thus freeing up current TV Band spectrum for new uses. This reallocation and repacking pro-cess will probably start around 2015, but could go on through to 2022. As this process may impact the whitespace re-served around TV channel 37, Ms. Liang-Chaboud encouraged AES members to write their congressperson regarding the needs of production wireless users.

Ms. Liang-Chaboud then went on to discuss options for dealing with the ongoing contraction of available spec-trum. The first band she talked about was the use of the 2.4 GHz spectrum, which is shared with Wi-Fi and other devic-es. Compared to the lower bands, 2.4 GHz has a reduced range, but devices in this range generally have the ability to frequency hop and can often work well despite competing with other devices. Shure's GLX-D system works in this range, as does Line 6's digital system. She pointed out that because 2.4 devices are often bursting devices, it's possible for multiple devices to share the bandwidth, depending on how heavy the usage is, and recommended doing a scan to determine how heavily used this frequency is in the area in which you wish to use your wireless microphone trans-mitters and receivers. She feels quite strongly that, "If you're going to do RF, you're doing yourself an injustice by not getting a frequency scan. You have to know what you're up against and if you don't have that information, it's just like walking in completely blind."

The second band she discussed is DECT, or Digital Enhanced Cordless Telecommunications. As Ms. Liang-Chaboud said, "The DECT band is not a lot of space, it's 10 MHz in the US, but Europe is lucky because they get twice that." DECT allows for time-slice allocation, so multiple devices can work together as long as they are properly clocked. Current devices operating in this band are cordless headsets such as Plantronics, and cordless phones, and they oper-ate in the 1920 to 1930 MHz band. Current wireless production products working in this band are Shure's Microflex and Revolabs Conferencing Boundary Mics system. In a relatively RF-quiet environment, it's possible to use as many as 40 wireless channels. Long term scans of at least 15 minutes must be done in order to ascertain what frequencies will be available, since devices will turn on and off and sometimes move around. The best time to run a scan like this is the same time of day as the proposed event, so you can determine what other activities are occurring around the space you'll be working in.

The Section would like to thank Ms. Liang-Chaboud for taking the time to speak with us about the changing landscape of managing wireless spectrum for live-sound applications.

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