AES Section Meeting Reports

Pacific Northwest - April 18, 2016

Meeting Topic:

Speaker Name:

Meeting Location:


The PNW Section's April meeting featured John Coulter (often known as JC) of the Seattle Center Sound Department, who spoke about wireless audio radio frequency coordination - managing your frequencies, scanning your RF environment and analyzing it, and coping with the ever increasing complexity of less bandwidth and more competition. The meeting involved members of the Art Institute of Seattle's Audio Club and Student AES Section. 13 AES members and 8 nonmembers attended.

PNW Chair Chris Deckard opened the meeting with news of future meetings and the election. He thanked the AIS Audio Club and AES Student Section for their help, especially Skyler Bendell and Atticus Ducharme. Per Section custom, all attendees briefly introduced themselves.

Seattle Center is a large public complex which was the former site of the 1962 World's Fair, and contains several of the city's major performance halls, KeyArena, public amenities and the well-known Space Needle.

Our Presenter, John Coulter (JC), has been a sound technician at the Seattle Center for 20 years, following a 10 year freelance career in the theater as a lighting designer, technical director, sound designer and technician. JC graduated from the University of South Carolina with a BFA in theater production in 1988. His regional experience includes audio work at Seattle Opera, Glimmerglass Opera, The Kennedy Center, and numerous touring productions. A career highlight was the visit of the Dalai Lama to Seattle in 2008, where John served as the personal wireless microphone technician for the Dalai Lama at numerous venues throughout the week. Since the opening of McCaw Hall in 2003, John has been a lead system tech for the hall, contributing to design, installation, repair and renovation of audio, video, communications and control systems. He is the lead wireless technician for the Starbucks Annual Meeting, the Gates Foundation Company Meeting, and other events throughout the year.

JC began by noting the tremendous growth in use of wireless audio in shows at Seattle Center in recent years, resulting in him being designated Wireless Frequency Coordinator for Seattle Center. He gave a nod to James Stoffo of Professional Wireless Systems, IAS software author, for some Powerpoint slides.

Recent years have seen turmoil in the wireless spectrum affecting the audio world. The transition to digital TV and emergence of wireless phone and data systems has led to FCC auctions of broadcast TV spectrum - and audio keeps losing radio space. Big money and speculation by investors other than wireless companies is rampant. He showed a little history of the FCC auctions. At one time, audio wireless worked nicely between bands (whitespaces) used by analog TV stations broadcasting over the air (OTA). With digital TV broadcasts, we lost our 700MHz mics, mainly to AT&T and Verizon. With the current auction, TV stations can effectively "sell" their band, and players like T-Mobile and new players are keenly interested in these bands.

While the FCC says it'll keep at least 2 channels open for pro audio use in each geographic area (unlicensed radios, 600Mhz band), that's hardly adequate for large-scale users. What's more, each geographic area will have unique spectrum usage. If you do a Google search about the current auction, you'll get lots of hits mainly from business reporting. There will be a 3 year transition period after the FCC finalizes the current auction.

What's a large, pro user supposed to do? The FCC would like you to get an FCC Part 74 license, which gives you certain capabilities, but only if you are using 50 or more frequencies. Seattle Center used a broker to help them get their license. Now they can reserve frequencies on a per event basis, and require whitespace users to shut down during that time. They can also run digital VHF devices, when they become available (products likely coming soon), and can run up to 250mW transmit power if they have to.

But small users won't get a license. They will have to adapt, checking databases of RF usage in their area. The FCC says such users can make frequency reservations (a month in advance), but licensed users have priority. Databases aren't always accurate. He listed some databases like those from manufacturers, and others like Sprectrumbridge, which is updated every 20 minutes.

For the past 10 years or so, JC has logged RF transmissions seen in his area. He suggested that everyone in this business must start scanning your local area to see what's going on. He showed spectrum scans from Winradio, and identified 2-ways, TV stations, mics, whitespace devices, and so on.

As to scanning hardware and software, about $1000-1500 can get you a decent hardware scanner with software such as Winradio. IAS (Intermodulation Analysis System) from James Stoffo/Professional Wireless/Masque Sound is the software standard, and costs $500 for a pro license. Shure software is good for high-end Shure systems and is free. Several handhelds like TTI Scanner are available. They can be handy, but have fewer features and are not much cheaper. RF Explorer was mentioned, $120 and a limited graphic interface, but can work with a computer, and costs $350 for a bundle.

JC then discussed how to coordinate frequencies for your event. Large operations will have a person assigned to do this, and there are more free-lancers now. He may do 50-60 frequencies for a Seattle Center event about every month. It's not just about finding radio space for your mics, intercoms, TV crews and so on, but finding spaces that will minimize intermodulation distortion that reduces your radio's signal quality.

Intermodulation distortion (Intermod, or IMD) are distortion products in the radio spectrum created by close carrier transmissions interacting. It's very troublesome, and can be very high with many mics closely spaced in a band. JC calls it "fur" on a scan. Most coordinators use the IAS software program to figure out how to minimize IMD with the desired frequencies. He offered a couple of tips: put all your radio mics in metal trays when not being on stage during the show. This isolates transmitters. Also, put your receiving antennas as close as possible to the action, and use lower power if possible, which increases battery life and reduces IMD in the spectrum.

JC offered suggestions for smaller users, too. Using the built-in mic autoscan usually works OK - write down any frequencies it suggests, and recheck often. The proper way to do autoscan with several mics is to turn off all mics, then turn on one at a time, scanning and synching for each additional mic. Then turn each mic off one at a time, in sequence, and see how much RF noise your array is creating. He calls this "war gaming." JC is constantly scanning his radio environment during a show looking for radio bogeys (transmissions) appearing.

After the snack break, some door prizes were given out.

After the prizes, JC demonstrated how he did coordination on a recent large show. He starts looking at known data on transmitters in his area, and sees how he can fit what he needs into available spectrum. He uses spreadsheets of known transmitter data in his area and the spectrum database coordinating software IAS, which does the calculations based on the known spectrum and the gear you want to use. He showed how he might avoid IMD and look for available spectrum for his gear by letting the software predict results in the spectrum. Not only does he have mics to deal with, but In Ear Monitors, intercoms, and TV crews with mics. He showed other examples of scans from recent shows.

Other comments and questions involved large facilities like convention centers with several events and sound companies. JC suggested seeing if they have a person doing frequency coordination, and IAS can work with schedules and multiple venues.

Written By:

More About Pacific Northwest Section

AES - Audio Engineering Society