Using Vantage with Shure® Wireless Workbench®

This brief video shows how Vantage, RF Venue’s OS X software for RF Explorer spectrum analyzers, can be used with Shure® Wireless Workbench® in a professional live production scenario to do some very useful things.

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We worked closely with Richard Stockton, a freelancer on a corporate gig with FOH Productions, to get screen recordings of Richard’s computer while he was setting up wireless at the show, switching back and forth between Vantage and Wireless Workbench.

This video shows you how to import wideband scans from Vantage into Workbench, how to perform IMD calculations within Workbench using Vantage scan data, and even a trick Richard has been using in conjunction with manual war-gaming.

Equipment used on the show included Shure UHF-R on the main stage, Shure QLX-D in the breakout rooms, and a mix of Radio Active Designs UV-1G and Tempest intercoms for the crew.

If you’re already using Wireless Workbench to network and/or coordinate your Shure brand wireless audio equipment, using Vantage in tandem with Workbench can allow you to do some things you would not be able to do with Workbench alone.

You can scan as wide as you want with Vantage + RF Explorer, and then import that scan into Workbench as you would from any other analyzer. (If you’re using a networked Shure receiver you are limited to the bandwidth of that receiver: J3, G5, H5, etc)
And since the refresh rate and resolution of Vantage’s interpretation of live RF Explorer data is so fine, you can use Vantage to zoom in on small portions of the spectrum to examine them. There may even be a way to tune cavity filters using RF Explorer + Vantage (forthcoming post!)

If you’ve never done any sort of software coordination whatsoever, using an RF Explorer as the spectrum analyzer for Vantage alongside Wireless Workbench is a very economical way to get into the game without losing out on some necessary features. Wireless Workbench is free. Vantage is $99, and RF Explorers, depending on the module, range from $100 to as high as $400.

Take a closer look and download a free 14 day trial for Vantage at the following link:

http://www.rfvenue.com/vantage

Is VHF the Answer to the Spectrum Crunch?

Last week Lectrosonics announced the release of the IFB-VHF, a 174-216 MHz tuned version of their popular IFB-UHF system.

(Which, by the way, has nothing to do with, and does not look like, the vintage marketing image from the old manufacturer Vega, shown above, and plenty more here.)

Of the new product, Lectrosonics President Karl Winkler said: “By adding the IFB system on the VHF frequencies, it allows users and system designers to move these out of the critical UHF band, which should improve the ability to coordinate larger systems even in a crowded RF environment.”

Lectrosonics is one of the first—but certainly not the last— major wireless audio manufacturers to reintroduce products in the VHF (30-300 MHz) band in an effort to ease the RF congestion at every large-scale production in UHF, and get a running start on the incentive auction’s decimation of 40-50% or more of current UHF spectrum available.

So far, these early second wave VHF devices are all non-performance devices—devices that wirelessly transmit some sort of audio or control that is not heard by the audience. (I say second wave because wireless audio began in VHF, and then migrated up to UHF in the mid to late 90s.) The only other major player to go VHF has been Radio Active Designs, with their successful UV-1G intercom system. There are no wireless microphones or monitors yet in VHF, though we might see some drop down to VHF sooner or later.

The announcement from Lectrosonics last week has got us thinking about VHF in general.

How suitable is it to performance and non-performance wireless audio gear?

What are the benefits of VHF over UHF?

And, crucially, if those benefits exist, can we expect them to last?

[NOTE: This discussion is mostly relevant to the United States and VHF spectrum in the US. Other regions may have different VHF allocations.

What is VHF?

“VHF” is defined by the ITU as radio waves between 30 MHz to 300 MHz. Go ahead and get yourself oriented with this supersized spectrum map.

Wireless audio users are not allowed free range across all 270 MHz that VHF theoretically offers. We are confined to empty VHF broadcast band DTV channels.

In a location where there are no VHF DTV channels, there are 76 MHz of spectrum available.

I want to repeat that. In the best case scenario VHF offers only 76 MHz of spectrum. By comparison, UHF currently offers 220 MHz, and 2.4 GHz around 86 MHz.

The VHF TV broadcast band is also non-contiguous; it is split into three bands (the highlighted blue bars in the chart above) containing 16 DTV channels separated by other services. “Low band” VHF, “mid band” VHF, and “high band” VHF. Low band extends from 54-72 MHz, mid band from 76-88, and high band from 174-216 MHz. Because the separation between low and mid band is so small (only 4 MHz) some lump both low and mid band VHF into simply “low band VHF” and call it 54-88 MHz.

The Pros of VHF

• Lower Traffic
  At the moment, VHF has fewer devices and fewer TV stations in it than UHF. During the DTV transition, many TV stations migrated up to UHF, abandoning VHF due to concerns over interference. Every major wireless audio manufacturer abandoned VHF by the mid 90s, so aside from RAD, Lectrosonics, and a few other products you might encounter on a production, like Comtek IFBs, VHF is a veritable oasis of solitude for low power wireless audio devices like wireless microphones and in-ear monitors. This is the main draw to VHF, and make no mistake: it’s a big one.

• Better Range
  Because of the propagation characteristics of VHF frequencies, signals are able to carry farther with the same amount of transmission energy than they are at UHF. Well-designed VHF equipment, operating with the same transmitter power, under the same conditions, and the same gain antenna, will travel farther than a UHF signal.

• Less In-Line Attenuation
  The generosity of VHF propagation extends into coaxial cables, too. You get much less in-line attenuation (signal loss inside cable) with VHF equipment than you do with UHF, which means you can do longer coaxial cable runs with fewer or no amplifiers, and use less expensive types of cable and expect the same performance.

Cons of VHF

• Larger Antennas & Components
  This is probably the biggest hangup. Because VHF frequencies have longer wavelengths, the devices themselves tend to be larger, heavier, and more expensive if they are engineered to the same quality standards as current-day UHF gear. For example, the wavelength of 180 MHz is about 5.5’. Whereas a 550 MHz signal has a wavelength of only 1.8’.

  Because of the long wavelengths of low band VHF (54-88 MHz), it’s unlikely that we’ll see much, if any, performance equipment manufactured there at all. Designing the antennas and electronics for a flawlessly reliable wireless microphone or in-ear for low band VHF are practically impossible without resorting to some wacky, expensive, and aesthetically unappealing tricks.

Non-performance equipment, like IFBs and intercoms however can use low-band VHF, since the audio quality of the audio feed is less critical. Comtek already offers a few products in that range.

• Incentive Auction Uncertainty
  There are still TV stations that use VHF frequencies. Most of them are public access or low power TV stations. But others may return.

  One of the “incentives” built into the incentive auctions is the option for a broadcaster to swap their UHF license for a VHF license and still get a payout. How many broadcasters will bite on that worm is yet to be seen. It’s possible that an uncertain number of current UHF stations will take the bait and move down to VHF, further crowding what is (remember) only 76 MHz.

• Low Power Pig Pile
  If all wireless audio manufacturers suddenly started making lots of gear in VHF, we’d have a problem.

  As James Stoffo once told me, “VHF is like that bar that used to be crowded, but now no one goes to anymore. There’s nothing wrong with the bar—it’s just that people have the perception that it was crowded, so they don’t go there anymore.” 

  If people (manufacturers) started going to the VHF bar again in droves, it would get crowded. And it would get crowded a lot faster than it took to crowd up UHF, because of its relatively small size.

  It might be argued the pig pile problem has happened in the last 1-2 years at 2.4 GHz. Since 2013, just about every major manufacturer has rolled out a 2.4 GHz band microphone.

  The result?

  It is very difficult to use multiple channels of 2.4 GHz microphones in any realistic venue. If you only need one 2.4 Gig mic—you’re fine. But need four, eight, or 12 channels of 2.4 wireless? Don’t look to tech support to solve that problem, look to religion; the 2.4 GHz ISM band is simply too utilized, even without adding a spectrum hogging microphone to the mix. WiFi and bluetooth devices use 2.4 GHz spectrum, too, and their use has exploded at 2.4 GHz even more than wireless audio.

• Higher Noise Floor
  In most locations, the noise floor at VHF is slightly higher than it is at UHF. The difference, though, is small. And the noise floor in a large-scale production is always going to be elevated.

IS VHF the Answer?

VHF is not “the” answer to wireless audio’s impending spectrum shortage. But it is one of several answers that, combined, will lead us out of the darkness ahead.

Future regulatory and technological seismic shifts will not allow us to keep all of our equipment exclusively in UHF for much longer.

Instead, the numerous low power wireless devices used in large-scale productions will have to fan out across the spectrum in combination with the correct deployment of tools like external antennas, filtration, and new modulation schemes if we are to continue to use them in the same quantities.

There is almost no other alternative.

Luckily, we’ve got RF options. We have VHF, we have the unlicensed bands at 900 MHz, 1.9 GHz, and 2.4 GHz, as well as (debatably) 5.8 GHz. There are plenty of additional bands open to holders of Part 74 and Part 90 licensees, as well as new bands that are slated to open to license holders post-auction, including the 169–172 MHz band, the 944–952 MHz band, the 941– 944 MHz and 952–960 MHz bands, the 1435–1525 MHz band, and the 6875–7125 MHz band. More on those here.

We won’t be kissing UHF goodbye, at least not yet. We’ll just be saying hello to unfamiliar spectrum elsewhere, making wireless production band-planning far more fragmented, but still doable.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

RF Venue Releases VANTAGE: OS X Spectrum Scanning and Monitoring Software for RF Explorer

We usually refrain from talking about our own products on this blog, but occasionally we need to make an exception.

Last week, we released a long anticipated native Macintosh OS X spectrum analysis and frequency monitoring application for use with RF Explorer® portable spectrum analyzers as well as RF Venue’s rack-based RF Explorer® RackPRO, called VANTAGE.

Vantage is the first professional third-party RF Explorer interface and coordination program that was built exclusively for the Macintosh OS X environment.

“For years, RF Explorer spectrum analyzers have been cost-effective, accurate analysis tools used by countless audio professionals and radio enthusiasts,” our CEO Chris Regan said after launch last week. “They allow visualization of the radio spectrum at a superb price, and connecting them to a computer through USB lets you do some very powerful things.”

“As Mac users ourselves, we’ve shared our customers’ interest in a robust, but very easy-to-use native Mac application for our RackPRO as well as the larger RF Explorer family of spectrum analyzers. Vantage will enable even the most novice wireless operators to visualize, monitor, and manage their facility’s RF systems without any steep learning curve.”

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The new software was designed with reliability and speed in mind.

Vantage is composed of three core features – spectrum scanning, frequency monitoring, and CSV file exports of scan data.

Users can manipulate scan range and monitor frequencies on the fly, and easily run Vantage uninterrupted in the background while using other programs simultaneously.

The export feature generates CSV files compatible with Shure Wireless Workbench® (WWB) and Professional Wireless Systems’ Intermodulation Analysis System® (IAS), so audio professionals can improve their existing coordination workflows in WWB and IAS by augmenting them with wideband scan data from an RF Explorer in any frequency range.

Vantage is compatible with the entire range of RF Explorer models. Depending on which RF Explorer is connected, Vantage can scan frequencies as low as 15 MHz, to as high as 6.1 GHz – filling a critical need for wideband scanning of the entire UHF broadcast band (470-698 MHz), as well as wireless systems operating in VHF, 900 MHz, and 2.4 GHz.

“RF Venue is committed to developing for the Mac and is continuing work on the Vantage codebase,” Chris continued, “with new advanced features planned to launch in the near future. We’ll be making new features available to all Vantage users via application upgrades.”

Vantage is available to try for free for 14 days at http://www.rfvenue.com/vantage, and priced at $99 per license.

13 Simple Tools Under $100 That Seriously Improve Wireless Audio Performance

Improving your wireless microphone or in-ear monitor system doesn’t have to be expensive. There are a lot reasonably priced accessories that might actually be more effective at improving range and reception than upgrading to the most expensive model from your favorite manufacturer.

1. Yamaha Sound Reinforcement Handbook

PRICE: Free-$24.16

The first two items on the list are knowledge resource tools, not things. (“Give a man a fish,” and so on…)

In January I polled about a dozen leading live sound engineers and professors at the country’s leading audio education programs for their most recommended books on professional audio.

Yamaha’s Sound Reinforcement Handbook made or topped the list with almost everyone. It’s been released in a few editions over the years, and is sometimes referred to as “the bible” of live sound.

New copies are available from Amazon, and free copies of outdated editions can be found as PDFs on the web.

2. Pete Erskine’s RF Coordination for Roadies

PRICE: Free

Pete Erskine, along with other wireless consultants like James Stoffo and Steve Caldwell, was among the first to pioneer wireless audio frequency coordination that was reliable and scalable for large broadcast and special events.

Pete’s brief manual RF Coordination for Roadies (click here for the mobile friendly link) has taught an entire generation of RF techs how RF coordination for IMD and other best practices are done. I consider it required reading for anyone who uses more than one channel.

Pete uses Professional Wireless System’s IAS and a small list of other quality tools to explain his process, though there are other tools available for those on a budget (like the RF Explorer in combination with IAS, listed later in this post).

3. Multi-Meter

PRICE: $30-$100

A multi-meter is an indispensable tool for tracking down problems with cables, among other things.

We demonstrated how to use a multi-meter set up as an ohm-meter to check for electrical shorts in coaxial cabling in this video:

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If you master Ohms Law, you can also do other things with a multi-meter, like tracking down and fixing broken components.

Multi-meters are priced from budget to ridiculous, but even simple analog ones should be more than enough.

Consider the Rolls MU118 to cover the basics, or the Paladin 1543 for more advanced continuity testing.

4. Ferrite Beads/Cores

PRICE: $2-$4

Ferrite cores and/or beads filter radio frequency interference collected by a cable unintentionally acting as an antenna while allowing audio signal to pass through. They are extremely useful for keeping out unwanted “cellphone buzz” as well as other kinds of mysterious interference. Some techs use them on every single input for complete protection from cable ingress. And at the price, why not?

I wrote an entire post on using ferrite cores to fight interference, and where to buy them, here.

5. WiFi Explorer

PRICE: $14.99

WiFi is more important to the audio pro than ever, and there are lots of new models of 2.4 GHz microphones that use the same spectrum bands as most WiFi. You can stumble around trying to get a signal for your board control or mic, or, you can use WiFi Explorer to know exactly what is going on, and what signal belongs to what router/WAP.

I learned about WiFi Explorer from Justin McClellan of Communication Handled. He posted on social about the importance of WiFi diagnostic tools, so I’ll let him explain it:

“Being an audio tech has now forced us to also learn some networking. Along with the hardwired networks we also have to deal with crowded venues when using wireless network systems to monitor and control gear.”

6. Brand-Name Batteries

PRICE: $0.65-$3 for AAs, each

There is probably some debate on this subject, and I think each individual has his or her own ritual when it comes to batteries. Namely, how to make absolutely sure that they don’t go dead while a mic is on stage.

But what can’t be debated is that brand-name batteries, on average, maintain their minimum voltage for longer periods of time than budget or generic batteries, and are also less likely to leak electrolytes or, when lithium is involved, explode.

Rhett Allain at Wired did an experiment on the differences between name-brand and off-brand batteries and their ability to hold a charge over time, and I defer to his results.

If your average on-stage time is less than one or two hours, and you (as many techs do) replace the batteries every single time that mic goes up on stage, and you have the money, and done the economics, maybe brand-name batteries don’t make sense for you.

Then again, why take the risk?

A good source for disposable and rechargable brand-name batteries that have been field tested for maximum life is Gotham Sound.

7. Bandpass Filters

PRICE: $30-$300

The (superb) performance of Anatech #AE548B9620 548 MHz bandpass filter.

Bandpass filters are external filters attached after the antenna but before the antenna input on a distributor or mic receiver’s front end, and strongly attenuate interference above and below a low and high frequency, which is called the “pass band.”

Adding a bandpass filter performs miracles when operating in crowded spectrum, or when a spectrum analyzer reveals strong interference very close to, but not on, the tuned frequency of a receiver.

Receiver’s have built in “tracking filters,” which are integrated circuits (microchips), that create a bandpass filter around whatever frequency you tune to. These tracking filters aren’t particularly good though, and they often aren’t narrow enough, or don’t have large enough attenuation to keep out-of-band interference from leaking into front-ends when that interference is really strong.

If you want to pack a large number of channels into a small amount of spectrum that is extremely crowded, supplementary filtration is about the only way to do it—though you really need to know what you’re doing.

Bandpass filters can also be used by less experienced users operating smaller systems as an extra layer of protection from nearby sources of interference of any type.

(the links to products are in this list, I just haven’t set up the formatting so you can see them yet! (apologies) Hover over the all caps words for the links.)

• Mini-Circuits Surface-Mount Bandpass Filters: $30-$50
  They’ve got the cheapest UHF band filters out there, starting at $30. Unfortunately their selection isn’t all that large, and none of the UHF stuff I could find was fitted with connectors, so using them is only possible for fixed applications, and you’ll need to know some electronics. Order HERE.
• Microwave Filter Co., 3278 Series Factory Tuned DTV-UHF Bandpass Cavity Filters: $215-$300.
  I know! More than $100, sorry. But these are really great. An EXCELLENT SERIES OF FILTERS that filter out everything outside of one DTV station—that is, everything around any 6 MHz UHF DTV channel is filtered out. You specify which station you want to filter when you order, and if you have a screwdriver and a spectrum analyzer with tracking generator, you can retune these babies to whatever 6 MHz pass-band you want.
• Anatech LC Bandpass Filters, 60 MHz Passband: $289-$355
  Anatech has AN AWESOME SELECTION OF CONNECTORIZED FILTERS with all sorts of passbands. They are a bit pricey because each one is made to order. JAMES STOFFO recommends the ones with 60 MHz passbands, which by mixing and matching let you get pretty close to aligning with the frequency bands of popular wireless manufacturer factory ranges.
• Professional Wireless Systems Custom Range Filter: $375
  I don’t care how far above $100 this is. PWS will custom tune AN AMAZING FILTER for you to whatever range you need. Unlike the other three companies mentioned above, PWS only makes products for wireless audio and, thus, has superb customer support and will always know what you’re talking about.

8. Blackwrap

PRICE: $25

Blackwrap (used by the lighting department, usually), or thick black aluminum foil, can be used to control troublesome radio frequency electromagnetic waves that cause interference by creating a radio wave “cage” around the offending device.

I wrote at length about how to use blackwrap to control RFI from video walls here, but it can be used to contain interference from any electronic device (circuit breaker, power supplies, etc) if you know where that naughty device is located.

9. BNC Coaxial Cable Termination Kit

PRICE: $85

Ever wanted to make you own custom length coax cables? Or salvage the good parts of a long length of coax that has one crushed portion or hole without throwing the whole thing away?

With this cable termination kit, now you can. Loosely follow these instructions, (your workflow will vary slightly if you use all the tools we suggest) and here’s what you’ll need:

(the links to products are in this list, I just haven’t set up the formatting so you can see them yet! (apologies) Hover over the all caps words for the links.)

• Stripper: To remove both insulation and dialectic to expose the center conductor (THIS is the same stripper we use to build RF Venue cables, it strips instantly, instead of taking 10-30 seconds. Highly recommended)
• Clippers or scissors: You may need to cut back the braided shield after you strip if the shield is too long for the ferrule. There are SPECIAL, INEXPENSIVE CLIPPERS available, but the wire on the braid is so thin an old pair of scissors work if you only plan on terminating a few, and don’t mind damage to your scissors.
• Crimper: THIS is a good budget crimper. The crimper we use to build RF Venue cables is THIS ONE.
• BNC Connectors: The actual connectors required for use with industry standard RG8X are 50 OHM MALE CRIMP-ON BNC.

10. ZAPD-1+

PRICE: $60

The Mini-Circuits ZAPD-1+ is an extremely versatile and low-cost RF distribution accessory that can be used to do all sorts of things. In fact, I wrote an entire post on all the cool things you can do with the ZAPD-1+.

11. RF Explorer

PRICE: $99-$300

Although the most popular (and recommended) model is $139, a tad over $100, the RF Explorer is just about the least expensive wide-band spectrum analyzer you can get. Depending on which model you purchase, it can scan as low as 15 MHz to as high as 6.1 GHz. You can use it to visualize spectrum all by itself, or plug it into a computer to do more powerful analysis and monitoring.

For PC users, you can use the RF Explorer Client or Clear Waves. For Mac OS X users, there is Vantage.

12. Connector Weatherproofing Kit

PRICE: $40

A grassroots attempt at weatherproofing a WiFi router using silicone, courtesy “Binary Koala”.

Most external wireless audio antennas are not designed to live outside, so it’s very important that if you do use antennas outside you weatherize them and, more importantly, the connectors and coaxial cable connecting the antenna so that moisture doesn’t seep into the cable or device.

Just a few drops of water inside a cable or connector can significantly alter the electrical characteristics and signal loss of an antenna and cable run.

If the antenna has an enclosure that covers the metal elements, you’ll want to seal every last open seam, hole, and juncture with silicone. Make sure to rub down these places with alcohol before applying the silicone for perfect adhesion.

Then, you’ll want to use heat shrink tubing combined with silicone to wrap up the connectors to make absolutely sure it’s completely impossible for water to get in.

(the links to products are in this list, I just haven’t set up the formatting so you can see them yet! (apologies) Hover over the all caps words for the links.)

• SILICONE
• HEAT SHRINK TUBING
• HEAT GUN FOR HEAT SHRINK

You can also protect antennas underneath an acrylic dome, although the domes are more expensive than aforementioned weatherization kit.

13. Fixed Attenuators

PRICE: $15-$50

Fixed attenuators weaken (attenuate) RF signal traveling through coaxial cable.

Why would you want to to weaken instead of strengthen signal?

First, to avoid overload on the front-end of wireless microphone receivers. Mic receivers are sensitive, and it’s easy for front-ends to encounter too much signal—like when a transmitter gets too close or when in-line amps are misused.

Second, a trick we learned from James Stoffo to alter signal-to-noise ratio on gigs where interference from video walls is problematic. Read about it here.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

How Adding an External Antenna Can Actually Make Wireless Problems Worse

External antennas are an incredibly effective tool for solving interference and dropout problems of all kinds.

But, it is possible to use an external antenna incorrectly in a way that increases problems instead of making them better, or use them in situations where their benefits are either unwarranted or inappropriate.

Amplification of Interfering Signals

When a stock whip/dipole antenna is replaced with an external antenna, and that antenna stays in the booth or FOH, performance improvements come mostly (but not entirely) from an increase in directional gain.

Directional coverage pattern of the 9 dBd CP Beam.

Directional gain is usually good, because of the effective amplification of signals in front of a directional antenna, but directional gain increases the signal strength of all signals within the antenna’s coverage pattern, not just yours.

Most external antennas are “directional” antennas—in that they have increased sensitivity to radio waves in one direction, and decreased sensitivity (rejection) in others.

A reference dipole antenna has a gain of 2.15 dB. A directional LPDA (aka paddle or shark fin) might have a gain of 4-7 dBd, and helical antennas are available with gains as much as 12 dBd.

High gain antennas increase the effective signal strength by increasing the density of radio energy in certain directions, similar to the way a lens or telescope focuses light into a small space (thereby increasing the apparent brightness to an observer) without increasing the amplitude of the source of the light itself.

Adding a directional antenna at the booth and pointing it at the stage usually makes things better because a directional antenna is “focusing” in on the transmitters on the stage and delivering a stronger signal of those transmitter signals to the receivers.

CP Beam helical antennas backstage, courtesy RMB Audio.

However, antennas aren’t intelligent. Antennas can’t differentiate your signal from someone else’s or a source of interference. If a source of interference (like a DTV station or noisy LED panel) falls in the same direction as the transmitter you want to pick up, the noise will be amplified just as much as the signal.

LED panels and TV stations are the most common culprits in this scenario, but unintentional interference can come from nearly any electronic device, and if another intentionally radiating device, like an intercom or microphone from a roaming news crew wanders into the coverage pattern of your directional antenna which were previously being attenuated, buckle up.

Transmit Antenna Contaminating Receive Antenna

In a rack, IEM transmitters often live right next to wireless microphone receivers. Letting IEMs and mics share a rack while using stock whips/dipoles can result in disastrous wireless because the IEMs are spitting out lots of RF while the mic receivers are trying to listen for very low amplitude RF coming from the stage. Cramped together in a metal cabinet is not the best place for the two species of device to live.

A solution is to separate IEMs and mics into different racks spaced a good distance apart, paired with both antenna combiners and distributors (great refresher at this link if these terms are confusing to you), each with their own separate antenna.

A transmit and receive antenna (CP Beam and Diversity Fin) deployed in Times Square, pointed in opposite directions, and offset horizontally, to avoid contamination.

Sometimes, techs might not separate mics and IEMs into separate racks, but know enough about RF to get rid of stock whips and feed the rack’s combiner outputs into an active signal/antenna combiner and the receiver outputs into an amplified antenna distributor. Unfortunately, if you place the external mic receive antenna and IEM transmit external antennas too close to one another, the comparatively high amplitude RF emitted from the IEM transmit antenna can easily bleed into the mics’ receive antenna, which is looking for very weak signals and may end up picking up or being overwhelmed by the IEMs instead.

We always advise our customers to place transmit and receive antennas at least 10 feet apart, minimum, to avoid unintentional interference between IEMs and mics, and never point the two directly at one another, no matter how far apart they are.

Improperly Deployed or Broken Cabling or Connectors

If you’re using an external antenna, you’re also using coaxial cable to connect that antenna to the receiver or antenna distributor.

There are more links in the signal chain, and therefore more links where mistakes can be made or equipment can malfunction.

When trouble occurs, cables and connectors are usually the last things to get inspected, when they should be the first!

Coaxial cable is fragile and easily damaged. The damage can occur inside the cable, or just as commonly at the BNC or SMA connectors terminating the cable on either side. If you have the resources, always check your cable to make sure they are transmitting RF signal properly.

I don’t have enough fingers on my hands to count the number of times we’ve tracked what a customer thought was a “bad antenna” to a severely damaged cable or missing center pin.

Long cable runs can also cause dropouts by reducing signal strength through in-line attenuation. The longer the cable run, the more in-line attenuation you get. Industry standard RG8X steals about 1 dB per 10 feet. 200 feet of RG8X reduces signal strength by about 20 dB (a lot). Even if you have a directional antenna attached to the front of that 200 foot run with 7 dB of gain, you’re still down 13 dB at the receiver, which can increase the likelihood of dropouts.

Active Antennas on Short Cable Runs

So called “active” antennas do not increase received signal strength at the antenna. Active antennas are just passive antennas with in-line amplifiers on the back.

They are not, should not, be used to “pick up more signal” because that’s not what they do. Rather, active antennas boost the amplitude of the signal gathered by the antenna in front of it to compensate for long, lossy feedlines. Much more on this common misconception here.

Active antennas can be very useful when cable runs longer than about 100 feet are in use, but when active antennas are used with short cable runs the signal delivered to the rack can easily be too strong, overwhelming the sensitive front-end of receivers and causing audible distortion or noise.

We frequently get calls from small venues, churches, and events where FOH or the rack position is near to the stage, and an active paddle is mounted on a small stand on top of the rack and connected to receivers with a 5 foot shorty—the perfect recipe for RF overload and ensuing screeching and hissing over the PA.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

The Tradeoff: Higher Gain Antenna, Narrower Beam-Width

One of the tradeoffs with high gain antennas is that the higher the gain, the narrower the beam of coverage. This is usually a good thing—but not always.

For example, the CP Beam has a gain of 9 dBd, creating a beam-width of 43°. This narrow beam width is exactly what you want if the antenna is positioned a reasonable distance away from the microphones or belt packs on stage (say, at FOH, or in the wings in monitor world). It provides increased range and reception by focusing more of the RF energy into that area. It also attenuates signals that fall outside of the beam, allowing you to strategically place helical and other high gain antennas and point them away from interference sources, like LED walls, and towards the signal of interest.

However, if a high gain antenna is placed in close proximity to talent using or wearing a wireless microphone or beltpack, the talent could move outside of the coverage area of the antenna, causing a dropout.

The CP Beam, actually, is not that directional, if you include the entire field of antenna design, and the polar plot above shows that it will still receive energy 360° around the element, but in differing amounts. In front of the element the CP Beam will increase the apparent signal strength of a signal, to the sides, it will moderately attenuate the signal.

There are antenna designs that have much sharper—nearly complete—rejection of off-axis signals, but we very rarely see these types of antennas in pro audio. The following polar plots show the extreme rejection of various types of “end-fire array” antennas.

End-fire array antenna patterns, the image of which mysteriously appears on WikiMedia with no author to attribute. The left most point of each of these patterns (where you see the small bouquet of smaller lobes, would be located at the center of the polar plots above. Now THAT’s rejection.*

The point is that antenna coverage patterns and (if specified) beam widths should be considered when setting up a system to ensure the antenna allows sufficient coverage for the movement of talent in a given space, especially if there is poor signal-to-noise ratio—which would, were the talent to wander off of the main axis of an antenna like the CP Beam, increase the chances of dropout.

An Omnidirectional Antenna with High Antenna Gain is Impossible to Construct

Lot’s of people want to have their cake, and eat it too. Which is why we’re writing this post, to clear up the misunderstanding; Many want an antenna that will focus RF energy equally in all directions—i.e. a high gain omnidirectional antenna that will provide higher gain and longer range in all directions.

This simply isn’t possible.

That higher gain antennas have narrower beam-widths is a function of physical laws. Engineers have been able to figure out some impressive and acrobatic designs for antennas that shape radio waves in incredible ways, but so far they have been unable to dupe the simple reality that if an antenna focuses RF more strongly in one direction, it will be less strong in another.

There are a number of omni-directional antennas on the market that claim to improve reception while providing an omni-directional coverage pattern. That is, they promise a single antenna will increase signal strength, and therefore increase range equally in all directions. These antennas are usually dipole antennas mounted in a housing that allows remote placement, but are otherwise no different than stock dipoles that ship with receivers.

Sometimes, these antennas are combined with integrated amplifiers and marketed as “high gain omni-directional antennas.” Such language is misleading because as we’ve learned, omni-directional antennas must, if you are using the correct mathematical definition of antenna gain, have low directional gain.

You can have an exceptionally well constructed and electrically efficient antenna with an omnidirectional pattern that may very well increase range, but it is not increasing range through directional gain, but rather in its ability to collect a greater percentage of available RF energy from the environment. For example, a half-wave dipole will probably collect more energy than a quarter wave whip (monopole) antenna that might be used as a lower cost stock antenna on some receivers.

You can also have a high gain antenna that radiates more strongly across one horizontal or vertical plane in degrees of one axis (elevation angles), but not others.

An example of a radiation pattern of a horizontally omnidirectional antenna
but still not truly (spherically) omnidirectional.

These are sometimes called “high gain omni-directional antennas,” and here the use of that term is more appropriate, but not truly omni-directional; the coverage area is like a horizontal pancake, or wheel, rather than an omni-directional sphere. (which, by the way, does not exist. Even the most evenly radiating dipole antenna still has two nulls located at the top and bottom of the element.)

Still, a lot of people want the best of both worlds. They want an antenna that will increase range while allowing their talent to roam wherever they please. That is in part why the Diversity Fin antenna, although not a single antenna, was designed and is now popular. It is effectively able to provide both directional and omni-directional coverage by combining two antenna elements on the same board, and the diversity receiver votes between which antenna has the best signal.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Leading image courtesy Seth Sawyers.

4 Proven Strategies for Fighting Video Wall RF Interference

1. Find the Interference.

Before you can fight interference, you must find it.

Finding a source or spurious radiation is not easy, no less on a stage crammed full of video walls, cables, and other stage machinery, because radio waves are invisible and inaudible.

A wireless receiver, on the face of it, provides only one clue—signal strength. And spectrum analyzers, even the pricey ones, can’t locate the source of interference all on their own.

But with a little help from you, and a directional antenna, both wireless receivers and spectrum analyzers can be transformed into powerful interference hunting tools.

The same RF tracking techniques used by wildlife biologists can be used by audio professionals
to locate RF interference.

We’ve written about the process at length before, without mentioning spectrum analyzers (which make the process a hell of a lot easier, btw) as well as the technique of “frequency dependent attenuation” DFI using a DIY tool: the handheld transistor radio.

The gist is that since directional antennas amplify radio signal in front of them, and attenuate radio signal arriving from the sides, they can be used as a kind of spotting scope for RF.

By connecting a directional antenna to the input of a spectrum analyzer or receiver and sweeping the antenna back and forth, you’ll either see (if looking at a spectrum analyzer or signal strength indicator on a receiver) or hear the interference (if listening on headphones or PA) when the antenna is pointed in the direction of the source, since the receiver/analyzer is “seeing” through the directional antenna.

Once you’ve got a direction where the interference sounds or looks strongest, walk forward a few steps, and repeat. The interference will continue to get stronger and stronger the closer you get, until you’re standing on top off, underneath, or in front of it.

Then the fun begins.

Sometimes, very rarely, you might know exactly what part of the device is the source of the leak, and rewire or solder it to a resolution.

Other times, also very rarely, you might be able to get permission to turn the device/component off or have it replaced, but only with political leverage and the good graces of a video director willing to forgo that component. (translation: impossible)

But for the most part you will have to use tools and techniques at your own disposal to resolve the interference without changing anything on the wall.

2. Use Blackwrap to Contain the Interference.

Blackwrap is a thick, black aluminum foil commonly used by lighting departments to wrap searing hot light fixtures up in the cats, to control stray illumination, etc.

Black wrap can also be used to control stray radio frequency electromagnetic waves, as well as light.

You are probably very familiar with blackwrap. But I, a lowly blogger, am not. I ordered some just to get my hands on it, and to do a crude demonstration of how one might go about wrapping a radiating component here at the office.

If you locate an offending device, cover as much the device as possible in blackwrap, or gaff tape a piece of blackwrap over the top.

Take this junction box for example:

It’s filled with electronics spitting out RFI.

And…

Voila! A newly shielded junction box—using nothing more than blackwrap and gaff.

The blackwrap acts as supplementary RF shielding and absorbs and reflects stray radio waves back at the device or inside the chamber of the blackwrap cocoon, instead of spewing out into the air and all over your receive antennas.

It’s best if you can cover the device in a way that the wrap makes minimal contact with metal components and connectors on or connected to the offending device’s enclosure. Contact with these parts could, under some circumstances, lead the blackwrap to function as an antenna and simply re-radiate that energy back out into the environment as if there were no blackwrap at all.

3. Use RF Attenuators to Push Down the Noise-Floor.

When broadband RFI from video walls raises the noise floor, but you still have good to great RF levels at the receivers, you can use fixed attenuators on your receive inputs to push the noise floor down closer to its native level or below the sensitivity of the receiver.

The signals get pushed down as well, of course, but because of the way receivers calculate acceptable signal strength and under what conditions to squelch, you’ll get improved signal out of your receivers.

Here’s how Radio Active Designs Chief Operating Officer James Stoffo (who gave me the tip), explains it:

“If the levels on your receivers are all pegged, which they should be, then you can put on attenuators, 3, 6, to even 10 db attenuators at your antenna input, and that pushes down the noise floor enough that, by adding 10 db of attenuation you increase range and increase audio quality.”

“It’s counterintuitive, but by adding attenuation you increase range, and that’s because analog receivers squelch on SINAD, so by adding attenuation, you’re increasing your SINAD ratio and getting better range and getting better audio.”

4. Use Directional Antenna Coverage Patterns to Your Advantage.

You can find interference using directional antennas, and you can avoid interference using directional antennas as well. In receive applications, by using directional antennas you can create selective cones of coverage that reach the performer and their beltpack or handheld, but not the video wall.

The directional coverage pattern of a helical antenna.

When it comes to using directional antennas specifically for avoiding video wall interference, circularly polarized helicals like the CP Beam and PWS Helical seem to be the weapons of choice.

Here, showing is much better than telling.

Again, much credit to James Stoffo for rig number one, and credit to Communication Handled and Stoffo for rig number two.

The green triangles represent the beam width of the helical antennas (not to scale). The pointy end is where the antenna is located, and the wide face that gradually tapers to white is the direction the antenna is pointed in.

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Video wall backplane image courtesy Sergio Leenan.

Unplugging the Mystery Behind (and Inside) Video Wall RF Interference

RF interference (RFI) from LED, LCD, and other types of display walls used in productions is a big problem for wireless audio. Some say the problem is getting better. Others say the problem is only getting worse. While few can say exactly why display walls create the type and quantity of interference they do.

But there is no denying the problem exists.

This article is about what display wall interference looks and sounds like, and what causes it. Our next article will provide detailed instructions on how to configure wireless audio systems to minimize the problem, so stay tuned.

Because video display walls are almost always on, around, behind, or (why not?) in front of performers and crew members using microphones, wireless monitors, and comms, this is a very tricky problem to solve since the source of interference is so proximate to the receivers or receive antennas in use. As we have said before there is almost no intentional or unintentional interference related problem that can’t be solved with creative use of the inverse square law. But because video walls are right next to performers, it’s difficult to get the beltpacks or antennas far enough away from the walls.

We’re not talking about a single LED display panel that you get at Best Buy, or even the expensive kind you might spec into an install. Here, we’re talking about walls. Giant video walls that have been torn down and built up from modular or independent components, or walls made from 10s or 100s of individual panels, like this:

What does display wall interference look and sound like?

Generally, wall interference is:

• Low Level. Video wall interference is usually low in strength or amplitude.
• Broad-band. Video wall interference almost always has a broadband footprint; it exists across a wide swath of the UHF spectrum, sometimes 100 MHz or more.
• Near-field. Video wall interference only lives within, approximately and conservatively (your video wall will vary), a 40 foot radius of the video wall or offending video wall component. Put another way, video wall interference does not travel far.

(But, there are exceptions, which we explore below.)

Here’s a simplified illustration of what you might find in a well-attenuated facility without any wall interference.

Typically, when a video display is on, you’ll see something like this:

To make matters worse, this interference is often present even if there is no image on the screen, and can vary wildly in its characteristics depending on the type of video signal being fed to the displays, and even the colors and movements of the images moving across the screen.

“What video wall interference generally does is raise the noise floor of the wireless,” says James Stoffo, Chief Operating Officer at Radio Active Designs. “Which gives you a poorer signal-to-noise ratio, which is going to reduce your range, and it’s also going to add audio noise to your system.”

James works on the high end of the production world. The interference he sees is coming from top quality displays, and display components, which usually produce this signature of a broadband, low-level “blanket” of spurious RF over the noise floor, and nothing else.

However, we have seen and heard considerable evidence from other professionals that poor quality, cheap display walls, especially LED walls, are capable of producing much more sinister narrowband RF “spurs,” which Ryan Sartell of Communication Handled described to us as LED “garbage.”

Here’s an illustration of what these spurs look like in some cases that we’ve seen:

These spurs can be very loud. Their amplitude may approach or exceed that of actual transmitters!—so they need to be addressed as if they were transmitters, carefully tuning around them and including them in IMD calculations.

They can also be quite wide. Pete Erskine of Best Audio sent us this scan he took at an event in Montpellier, France, which he reports, “almost destroyed my show.”

This is the third image we have seen showing these spurs. At Pete’s show, there were 5 MHz wide spurs every 20 MHz. Other scans show spurs with different widths and spacings, but they are definitely real.

What causes these spurs? We don’t know, exactly. Tim Vear at Shure has speculated LED drivers are the source of the spurs. Pete thinks they could possibly be from badly filtered switching power supplies with non-shielded connectors (more on these in the next section BTW).

If you think you know the answer to the spur mystery, please tell us more in the comments below.

Display wall interference also has a characteristic sound if the RF demodulates and makes it into the audio. Some have told us the worst audible artifacts sound like “digital jittering” (though we don’t have any recordings to give you unfortunately). Other describe it as being like the sound of light sabers.

James explains that the higher RF noise floor also creates a low level rise in the audio noise floor that sounds like “increased breathing and pumping in the audio.”

“Since this interference is broadband, you can’t filter it out, or you’ll filter out your mic,” so you’re stuck with both compromised reception and constant audible artifacts.

All told, video walls can be just about the worst thing that can happen to an audio department.

What causes display wall interference?

This was not an especially easy question to answer. Although everyone who works in production audio has encountered display wall RFI, very few seem to know why it occurs. And the people who do know have slightly differing opinions.

It should be said blame for RFI is not always easily pinpointed to one person, device, or company, but is the product of an accumulation of causes that begins when a panel is being designed, continues through how they are manufactured, and ultimately ends in how they are configured and installed at the venue by the crew.

Likewise, a video wall used in production, as compared with one single panel, is a system of interlocking parts that all use electricity which all have the potential to create interference, so it’s not easy to simply point to one individual electronic component and say, “yep, there’s your problem.”

Let’s begin with a summary of possible causes, and then move on to in-depth analysis with expert testimony.

• Power supplies: Power supplies are always a common source of RFI. Today’s video displays are truly gigantic, and all that video needs a lot of electricity, which means a lot of power supplies. LEDs especially need sophisticated power supplies that contain, in addition to the usual suspect components like transformers, switching regulators and other dense circuitry that can, if poorly designed, contribute RFI.
• Poorly or unshielded cable: Display walls use an absurd amount of cabling, cables of all types and sizes, that crisscross one another: a recipe for RF disaster. Potential offenders might include high voltage lines, all the way down to the thin cables that are carrying high frequency signal to individual diodes.
• Electrical junction boxes: Which may be on the wall itself or somewhere else on or underneath the stage.
• Unshielded connectors: Connectors are a great spot for RFI to leak out of. Display walls use a lot of connectors to snap together all of the parts listed above.
• LED drivers: LED walls create moving images by chopping video signal into on/off signals sent to individual diodes using pulse width modulation (PWM), at (relative to standard 60 or 120 Hz video signal) very high frequencies, up to 3000 Hz. These drivers can create interference by themselves if poorly designed or programmed, or if the wires delivering their high frequency signals aren’t properly configured.
• Poorly shielded or non existent backplanes: Electronics that emit large amounts of spurious RF use PCB boards, either functionally or as a protective groundplane, built with many layers of copper to keep the RF contained within the device, or to absorb the RF and diffuse it through the ground. The more layers you have, the better the protection, but, the higher the cost.

There is wide, wide variability in the quality of display panels available for sale. Generally, it seems that price is correlated with the care of electronics design; poor shielding and grounding and sloppy PCB design leads to RFI, plain and simple.

Older panels, and panels manufactured in Asia tend to create more RFI than newer panels, and panels made in Europe or the US.

“A lot of LED products that might come out of China use the minimum minimum minimum number of PCB layers possible, just to make it inexpensive,” says Jeremy Hochman, who currently leads creative LED product development at VER. “They’re using the minimum you need to make it operational, and that’s it. You then have very high-speed signals in the megahertz range going through the board that are all just on the surface of the PCB, or coming out through cables, going who knows where, and making weird patterns, that contribute to interference.”

Jeremy, who like James Stoffo works with and designs some of the best panels available, claims that from his frame of reference, things from manufacturers are getting better.

“I would say 90% of the products I see these days are LED, and things there are actually getting very good. LED drivers are doing a lot more of the smarts close to the LED, so the signals running on the PCBs are not so high-speed. That reduces EMI. The enclosure technology is getting better. Better groundplanes are being put on the LED boards.”

While the design of individual display products, especially cheap ones, do cause some of the problem, that’s not the entire story. The user also has something to do with it.

“There’s no way to know how an end user that might be decoupled two or three times from the manufacturer is going to end up putting this thing together,” continues Jeremy. “I don’t think this interference is particularly caused by the LED panels themselves. It’s the sheer volume of them. If you take 1000 toasters and put them in an array, they’re probably going to radiate in an unexpected way. If I set up 1000 projectors in a modular array, it’s probably going to interfere with you. Many older products weren’t intended to be set up on such a large scale, so if I set up an LCD wall that’s 300 feet wide, it’s going to radiate and interfere.”

Video departments are doing some very severe teardown and rebuilds of video components to get their displays just they way they want them. They may be replacing or adding power supplies, gutting and re-wiring diodes or panels, or even swapping out or re-programming drivers—and they aren’t checking to make sure their Frankenstein creations, however gorgeous the image, are conforming to FCC certifications for acceptable levels of spurious RF emissions.

James Stoffo has been singing this sad, sad song for a long time.

“When I originally started going up against video directors,” he remembers, “the first thing they would say is, ‘well, the equipment is FCC type accepted.’ They would point out the FCC acceptance label on the back of the unit.”

Since LED display walls used in production contexts are so much different than consumer LED or LCD display products used in the home, and since production caliber displays, even the best ones that are put together by expert video departments, are still causing devastating interference to the audio department, perhaps it’s time the FCC takes another look at how it categorizes and approves EMI on these types of products.

“The tolerance on the FCC type acceptance on this equipment needs to be tightened up,” James Stoffo asserts, “because even though it is type accepted, it is still creating harmful interference onto wireless mics, ears, and intercoms.”

Now might be the time to start getting tough on the problem of video wall RFI—before it gets any worse.

Leading image courtesy Lara Torvi.
Video wall backplane image courtesy Sergio Leenan.
Close-up of diodes courtesy “Syntropy.”
Video wall installation image courtesy Niv Singer.

Protect Antennas and Wireless Gear from Rain, Basketballs, and Other Hazards with Transparent Domes

We often receive calls from installed A/V professionals looking for a way to mount one of our external antennas safely in a school gymnasium, or outdoors somewhere in an ideal location but safe from the rain.

You shouldn’t completely enclose an antenna in anything if you want it to work well. And using protective covers made from wire or mesh is almost guaranteed to cause wireless problems.

That’s why we were thrilled to learn of a solution that Dave Kint, Vice President of dk communications, inc., discovered in the course of working with some of his clients out in Colorado: an affordable transparent dome made of special acrylic.

Dk communications is up to some cool stuff, and Dave has high standards. He knew he needed to mount his Diversity Fin and WiFi router in an ideal, lofted position for excellent line-of-sight, and protect them from wind, rain, basketballs, footballs, and baseballs in the multiple school gymnasium and football field venues he has as clients, without sacrificing wireless performance. Plus, why not try and actually make it look good, too?

After a bit of research, Dave found California Quality Plastics, which manufactures a durable, RF permeable clear acrylic hemisphere/dome that fits over an external wireless antenna and easily mounts to any architectural surface. Dave uses the 24” diameter model, part HEMI24. Navigate directly to this model by clicking here.

“Before we found these domes,” Dave explains, “we really didn’t have anything that would allow us to put antennas in an area where it was going to be susceptible to some sort of damage or impact. I’ve talked to other people about non-metallic metal boxes, but, that didn’t really pan out. They are very expensive, and the other problem is that there’s nothing that’s really of adequate size for the antenna to fit inside.”

Dave notes that California Quality Plastics hemispheres are UV resistant, so they won’t become brittle or discolored after years of sitting out in the hot sun. There’s also enough space for dk to include other wireless gear: “We also were able to put the Apple Extreme under the same antenna dome so that we could use that for Airplay connection and system WiFi control of the DSP controller.”

Typically, we don’t recommend placing wireless devices so close to one another, because of the risk of out-of-band interference bleed over, as well as the metal in the Apple device altering the electrical characteristics of the Diversity Fin.

But, he says it works great and the DFIN is as effective as ever.

Thanks for the tip Dave!

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Vintage Vega Wireless Microphone Ads from the ’70s and ’80s

This Saturday I spent a few hours browsing the meticulously organized files found at the sound industry’s archives: the Audio History Library & Museum.

We are building a basic historical database of wireless microphone prices—which will be the subject of a forthcoming post. Among them were many vintage advertisements for wireless audio equipment of all sorts from every manufacturer. These ads ranged from historically significant, to hilarious, to downright painful.

As many seasoned pros remember, Vega was among the first commercial scale wireless microphone manufacturers, and for many years had market dominance. Since they no longer exist, we think it safe to share some of the early promotional materials dug up from this valuable collection.

I think we can all share a laugh at how far the technology—and marketing sophistication—of wireless audio has come over the years without cheapening the powerful contributions Vega wireless made to the industry.

Enjoy!

The first five are pages from a brochure on all four—count them—four of Vega’s models from around 1975: “The Orator,” “The Professional I,” “The Professional II,” and “The Performer,” which is advertised as “A microphone, transmitter, and antenna, all in one!”

Vega seems to refer to their entire line as “The Cordless Mike, by Vega,” which goes to show how few wireless microphones were on the market at the time, or, just how gigantic a market share Vega owned. That would be like referring to the iPhone or Droid lines as “The Smartphone.”

Up next is the “Professional 55,” which seems to be aimed at broadcasters.

Then we have the “Ranger” and its delightful camp-western magazine spread.

Finally, the “Q Plus Professional Wireless Intercom,” which rewards with a stoic portrait of an end-user.

Just look at those cold, responsible eyes.

It’s as if years and years on the road have desiccated his soul. All human desires and whimsy have been wrung out. What we see is an automaton molded from the old dregs of what was once a man; a sinless, empty being of the night that subsists on dry Folger’s crystals straight from the package and the vapors of an A2’s smoldering Pall Mall. That lives for nothing—

NOTHING—

but the cue.

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