Do Cellphones and WiFi Interfere With Wireless Audio Equipment?

Yes and no—but mostly no.

Cellphones using spectrum owned by wireless carriers for voice or data never intentionally interfere with wireless audio, but can unintentionally interfere through the dreaded “GSM buzz.” (the distinction between intentional and unintentional radiators is here)

WiFi devices—including cellphones that are WiFi capable—can and do interfere with wireless microphones, but only with mics using the 2.4 GHz band, which are less common than industry standard UHF mics.

Cellphone Interference

For all practical purposes, cellular transmissions do not directly interfere with wireless audio devices.

If you are blaming cellphones for wireless problems other than GSM buzz, that blame is probably misplaced.

The majority of wireless microphones use UHF broadcast band frequencies between 470-698 MHz. Almost all cellular networks use frequencies located a safe distance away from UHF microphones. And there are no licensed cellular networks that share frequencies with UHF mics.

It’s possible for interference to bleed out of a given band into an adjacent or nearby band. This is called an “out of band emission.” However there aren’t any active cellular bands anywhere remotely near the UHF range.

It’s also possible for cellphones using WiFi to interfere with 2.4 GHz microphones, which we discuss in the next section.

Where are cellphones? All over the place, depending on model, manufacturer, carrier, and region.

As you can see (actually, you probably can’t—click here for a supersize version of this chart) licensed cellular spectrum does not overlap with current UHF. You can also see 2.4 GHz unlicensed waaaaaay to the right. A zigzag line is used to denote cellular bands, as they are mixed in-between other services.

The 700 MHz band was auctioned to carriers in 2008, and the lower portion of that allocation is close to the upper regions of UHF, but few of the winners have built up active networks there, so we don’t have to worry about out-of-band emissions (yet).

Some of you remember the blip blip blip bzzzzzzz sound that preceded incoming cell phone calls in the early to mid 2000s, which was known variously as the “blackberry buzz” or “GSM buzz,” and laid waste to unsuspecting PA systems.

The buzz was a radio communication protocol used by some (especially 2G) GSM type networks that would, under certain circumstances, be converted from electromagnetic energy into audio frequency signal by unshielded wires within electronics acting as antennas in combination with diodes and transistors, and then made audible by speakers.

Some believed that the dreaded buzz was caused by cell phones “taking” mic frequencies. In reality this type of interference is unintentional and caused by electrical interactions between cellphones in close proximity to XLR cables, speakers, and PA systems.

With new protocols like 4G/LTE, GSM buzz is now rare. I haven’t heard it in years (have you? email me, because I would like to know if it still happens)

[UPDATE: After a few emails, GSM buzz may be a more significant problem than is led on in this article. Stay tuned. DOUBLE UPDATE: An important follow up article is here.]

WiFi Interference

WiFi devices, like wireless routers/WAPs, can easily interfere with wireless audio equipment, but only equipment that operates in the 2.4 GHz band. UHF broadcast band equipment using 470-698 MHz is not adversely affected by WiFi.

Most (but not all) WiFi equipment uses unlicensed frequencies on the 2.4 GHz ISM band, which in the United States stretches from 2.400 GHz to 2.483 GHz. The most familiar standalone WiFi device is the wireless router or WAP. But Bluetooth, Zigbee, and many other radio technologies use 2.4 GHz.

2.4 GHz band wireless audio gear includes Line6 microphones, the Sennheiser EW-D1, the AKG DMS-Tetrad, the Shure GLX-D, Tempest 2.4 GHz intercoms, and a few others.

2.4 GHz microphones have grown in popularity because they require very little frequency coordination and are legal and unlicensed in every international region.

However, 2.4 GHz is a crowded band, and most technology operating there does not require real-time uninterrupted operation, like wireless mics do.

One or two channel 2.4 GHz microphone systems usually perform well. But interference may become problematic on multi-channel systems or where WiFi utilization is intense.

Since WiFi is such a prominent feature on smartphones, the 2.4 GHz band is hostile territory anywhere there are lots of people and WAPs that offer up connectivity. Smartphones aren’t just using WiFi for internet access. Increasingly, phones make calls through dedicated “voice over WiFi” apps or through what’s known as WiFi offloading.

Controlling interference from WiFi is difficult for two reasons.

First, WiFi sends out rapid bursts of RF that constantly and unpredictably hop frequencies—unlike analog transmitters which stay on a single frequency. You can’t manually coordinate around a WiFi device because it doesn’t stay put.

Second, WiFi is everywhere and used by everyone, but controlled by few. You have no authority to ask IT departments and cellphone owners to stop transmitting, and no opportunity to coordinate with them. Even if you did, short of completely powering them down, smartphones and other consumer WiFi radios operate automatically and out of direct control.

It is worth noting that both WiFi and cellphones can cause spurious interference to wireless microphones of any type by way of malfunctioning power supplies and poorly designed or shielded electronic components. But this risk comes from anything that uses electricity. Low power cell phones and routers manufactured to tight specifications are much less likely to cause spurious interference than things like faulty electrical wiring, breakers, audio amplifiers, and power lines, so if you are constantly worried about cellular and WiFi as a source of interference aside from the characteristic GSM buzz—you shouldn’t be.

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

Don’t Let Rehearsals Fool Your Wireless Microphone

Too often, we receive worried calls from techs or FOH engineers that go a little something like this: “We set up and coordinated our wireless during rehearsals on Tuesday, but on Sunday we had the worst dropouts! What’s going on?”

Usually, new variables absent during rehearsal have changed the shape and behavior of the radio environment, causing equipment to fail, even if settings are unchanged.

There is no practical way to replicate the RF environment of a full auditorium during an empty rehearsal.

There is, however, ample evidence for what can be expected to go wrong, so you can take steps to avoid it.

Higher noise floor

When 500 people and their cellphones pack into a building, security and staff power on two-way radios, and stage lights and LED walls turns on, the noise floor of the UHF band typically goes up, even if there aren’t any new wireless audio devices using UHF added to the mix.

Although an increased noise floor may not create dropouts on its own, it raises a mic or IEM’s general susceptibility to other sources of interference.

Technical Director Daniel Scotti and the team at Saddleback Church worked with us to illustrate just how much RF conditions can change between an empty room and a full one.

Here’s a frequency scan using an RF Explorer RackPRO and Clear Waves of Saddleback’s main sanctuary on a Saturday before services, with everything powered down.

And here it is on a Sunday, first during a pre-service run through with mics and IEMs powered on, and then during the actual service.

We scanned the entire UHF broadcast band, 470-698 MHz, so visually these results don’t look as dramatic as they might were we examining only a few MHz, but a significant difference is there. The noise floor rises once devices are powered on, and rises in some places again when the audience is present and service underway.

If frequency coordination was sloppy during rehearsal, its faults can rear up during the actual performance when there is less headroom between the signal of interest and noise.

Frequency coordination during rehearsals should follow best practices and use software programs like Clear Waves or PWS’ IAS to calculate intermodulation products to make frequencies as reliable as possible, rather than “good enough.” Techs should assume RF conditions on the day of the performance will be much worse than they are with an empty building.

Performances in urban areas should also consider the possibility that neighboring groups may also be using wireless audio equipment at the same time. Although wireless microphones are low power, they can still cause interference over short distances or between adjacent buildings.

Is there a concert scheduled for Saturday night at the club across the street? Is there another church also holding services on Sunday at 11:00 AM next door?

If so, consider reaching out to them to exchange frequency lists to ensure you won’t step on one another’s toes.

Line of sight

Wireless audio devices need an unobstructed path between the handheld or beltpack and the antenna back at the rack or remote antenna location. Radio waves are absorbed by human bodies. A human body in-between receive and transmit antennas is not good.

Although we see line-of-sight problems in all markets, it seems to be a big problem for houses of worship. Maybe because audience members do a lot of standing up and sitting down.

“Antennas are often set too low,” says Kent Margraves of WAVE, a top-notch integrator based out of North Carolina specializing in houses of worship, including Saddleback. “FOH guys don’t want to put antennas up on stands, but that’s a terrible mistake.”

External antennas are kept discreetly at eye level, just above the heads of seated audience members. As soon as the first rows in front of the FOH position get up, that clean line-of-sight signal gets snipped.

Saddleback was also kind enough to give us comparison scans for when the audience was seated vs when they were standing.

We’ve circled an area around 550-580 MHz where the physical changes caused by audience position dramatically attenuate received signal strength.

External antennas should be on stands well above the tallest audience member with a clear view of the stage. They can also be mounted anywhere within the facility that also provides line-of-sight—like on walls or ceilings—using long runs of low-loss coaxial cable or an RFoF system like the RF Optix.

“The best systems are not installed FOH at all,” continues Kent. “The receivers are backstage in a production rack and the antennas are flown beside or above stage.”

But we assume you’re using external antennas in the first place. Much worse than a low flying external is burying stock whip/dipole antennas in a closed rack housing, or scattering receivers around the booth.

Radio interference on or around the stage

Any kind of electronic device has the potential to create harmful radio interference. Most devices emit some kind of RFI, but the ones up on the stage are most likely to interfere with wireless audio equipment (especially IEM belt packs) because of their proximity, so the stage should be checked and checked again for culprits.

Bands carry all sorts of troublemakers with them everywhere they go. Amps, keyboards, pedals, effects processors, can all produce powerful interference, whether they are malfunctioning or not. If possible, choose frequencies when all the band’s equipment is powered up.

Kent suggests band members and anyone else allowed onstage be required to leave personal electronics in the greenroom. He also suggests vetting mixing equipment brought by the band for interference before letting it up onstage.

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

Leading image courtesy Chris Fenton.

Journey to the Center Conductor

A few days back we got an email from an engineer in Spain about whether our RF Optix fiber optic remote antenna system is compatible with a so-called “leaky coax” system in an underground mining communications installation.

Just when I think I’ve heard about every sub-field this tiny industry has to offer, another, even more obscure one emerges.

Leaky coax though, also known as radiating coax, really isn’t that obscure—we just don’t hear much about it at RF Venue.

Radiating coax allows RF to go where RF shouldn’t go at all: in the depths of a mine, on subway platforms, freeway tunnels, military bunkers, aircraft carriers, nuclear reactors, and more.

“The purpose of ordinary coaxial cable is to contain radio waves inside the cable,” says Tony Fedor, a Product Manager of cable at Times Microwave Systems. “The purpose of radiating coax is to let it leak out. It’s like having a continuous antenna where antennas aren’t practical.”

When connected to a radio, the exposed inner conductor in a length of radiating coax works like one long antenna. The metal shielding is deliberately absent, or selectively perforated or shaped to allow RF signal out into the environment at very low powers, or, in receive applications, expose the conductor to energy. Cable is laid out wherever RF coverage is needed.

There are many different kinds of radiating coax. Some are designed for specific frequency ranges, others have different loss characteristics, or types of connectors. The figure below is of Times Microwave’s popular T-Rad line.

It’s a little hard to see, but the shielding is split lengthwise and peeled back, making a semicircular sheath around the center conductor.

Mine communications may be one of the largest and oldest markets, but radiating cable is useful anywhere antennas are difficult to install and radio waves have difficulty propagating.

Applications range from mundane to exotic.

New York City and other major metropolitan areas have miles and miles of the stuff lining subway platform and tunnel walls so police, emergency personnel, and construction workers can communicate with the world above.

Tony tells me how Times Microwave supplied cable to a group that installs and services nuclear reactors, so they can keep in touch with people walking around in hazard suits inside the facility. Two-way radios are useless without leaky coax because of thick radiation shielded walls and airlocks.

It’s also buried around top secret facilities and used a covert perimeter detection system. A sensitive electromagnetic field hovers around the cable. Anyone that passes through the field changes the capacitive yield of the system and is perceived by monitoring software hooked up to the line.

There are even applications in sports and entertainment.

“We’re working with a company that has RFID tags embedded in golf balls,” says Tony. “They have a driving range with coax down the length of it that allows golfers to know precisely how far their ball has gone. They set up driving contests, and other games.”

Though the principle behind radiating coax is an easy one, in practice designing radio systems that use leaky coax is difficult. The biggest challenges are loss of signal strength (it is leaking after all), and coupling loss from imperfect connections.

All sorts of powered distribution thingamabobs are in this literally dark corner of the wireless industry to get around the problem. Just search “leaky feeder amplified distribution system.”

I asked Tony whether there were expert leaky coax design engineers who might talk to me about their work.

“They tend to be very secretive about what they do, and reluctant to give up much information—I’ve tried,” he said. “They only describe leaky coax as a ‘black art.’”

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

The Time to Get Licensed Is Now

With the 600 MHz auction knocking, it has never been more important for large-scale users of wireless audio devices to get a Part 74 license. Thanks to regulatory changes, publicly available resources, and a streamlined licensing service recently launched by our partner Professional Wireless Systems, getting a license is easier than ever.

It used to be that only those working in the broadcast and film industries could get one of these. Good news arrived last year when FCC broadened eligibility criteria to include professional sound companies and operators of large venues that routinely use 50 or more wireless microphones. Now, just about every wireless “power user” has access to licensed status.

Getting licensed allows more powerful transmitters (up to 250 mW) and priority registration on the TVBD white space database, which protects against interference from TVBDs.

But there is another seldom discussed benefit that is just as relevant.

“As an industry we need to be better represented in the FCC’s system,” says Cameron Stuckey, of Professional Wireless. “One of the reasons the 700 MHz range was taken back so abruptly was that when the FCC did their due diligence and examined the spectrum they found only a couple hundred licensed Part 74 users and said ‘great, this isn’t going to bother anyone.’”

Cameron explains that when it comes to voicing opinions on pending regulations, users who have a callsign have big advantages over those who don’t.

Anyone who buys a wireless microphone off the shelf is by default operating as a Part 15 or “unlicensed” user. Were such a user to submit a comment on a Commission item, from the perspective of the FCC they seem like “just an average citizen,” he says.

“It’s a totally different paradigm when you have 500 licensed users of the spectrum voicing the same opinion compared to 500 ordinary citizens trying to sway the FCC. If you file a comment and you have a callsign as a licensed user they are required to read through your comment and take it seriously in the debate.”

If you value your ability to operate lots of wireless post-auction, it behooves you to hop on the license train ASAP both for the technical and political benefits a license potentially provides.

You can apply for a license on your own, especially if you are a location sound mixer or broadcast professional. That path is well trodden and there is even a handy step-by-step guide prepared by IATSE 695 for those who want to go it alone.

But even those who do qualify and are aware of licensure have been hampered by the bureaucratic requirements of the application process, along with technical glitches that plague the FCC’s tragically outdated online software.

PWS spares organizations (for which the process is slightly different than the IATSE link above) from facing off with this notoriously difficult process.

“We have a true turnkey system for getting licensed,” explains Cameron. “There is a brief security form, just like if you were buying anything else, where you put in your name and mailing address and a few other details.”

PWS then handles the rest, and your license arrives a number of weeks or months later.

The service is offered at a flat rate of $600, which includes the FCC’s $160 filing fee. Contact PWS at FCClicensing@professionalwireless.com for more information.

Leading image courtesy Christopher Skor.

Just How Dead Is the Recording Industry?

While having dinner with a friend, Tony Falco, and his wife Liz, he mentioned that he is actively looking for a space to record. I rattled off a few pessimisms about the anemic state of the recording industry, and received a well-deserved eyebrow from Tony.

I have no personal or professional experience in, or aspirations to, recording. But I have heard about it.

Mostly, I hear bad things: that recording is “dead” or “dying,” wounded first by DAWs, and then killed off in 2008.

That’s why Tony’s plan surprised me. Why would you open a recording studio in this day and age, and actually expect to make any money from it? Tony, a drum performance graduate of the New England Conservatory of Music, is anything but naive about music careers.

It surprised me so much that I thought I would investigate my assumptions.

So, can you still make money opening and running an independent studio?

The first thing I did was give Tony a call to get his thoughts on paper. Why dream of opening a studio?

“If,” he told me, “you recently invested in physical gear and traditional education with the sole intent of becoming an audio engineer and opening a studio, the accessibility of software tools and an abundance of used gear probably did kill the dream in that respect.”

It’s old news that the introduction of affordable digital audio workstations like Pro Tools in the late 90s heralded the beginning of the end for old ways of making records, and the obliteration of many of the iconic big studios.

“For me,” continued Tony, “it’s not all about recording. A studio is just one of the pieces that fits together to make my life as a musician work. I’m making an investment in software, equipment, and space for what it would take to record a single album, and then I also have a space that separates my personal and professional lives where I can practice and teach.”

For many musicians and engineers like Tony, a studio is no longer a viable means of deriving the majority of an income, but can very easily be one of many different income streams in a way that was not possible before, because the equipment overhead is so much lower. Likewise, a specialized recording or mastering engineer who does nothing but record or master is now rare, while combinations of engineer/musician/entrepreneur/hobbyist proliferate.

When I asked Matt McArthur, Executive Director of Boston area non-profit studio The Record Company, on the possibility of running a profitable studio he promptly said, “absolutely, but it’s different than it used to be.”

“Because it is so difficult to derive a good margin—or any margin—from the sale of recorded material, the role of the recording studio has changed. It used to be the recording studio was something that artists and labels invested in on speculation that they would be able to produce a return on the product they created. While there are some successful artists in the world who still do sell records, for the most part making records is now a marketing expense.”

For his own enterprise, Matt applied a non-traditional business model—the non-profit—to a recording studio around a unique mission, to “amplify Boston’s diverse musical voices.”

The Record Company is a success because it approaches recording from a framework that acknowledges just how much the industry has changed. Like Tony, Matt is able to make recording financially “work” by fitting recording services in with other strategies. Their non-profit status allows them to accept donations, and they also rely on clients to provide their own freelance engineers, rather than keeping an in-house engineer.

Matt told me other studios have been able to survive as standalone, for-profit shops by doing the opposite: staffing a skilled engineer and maintaining margins by charging a premium hourly fee for his/her services either to professional musicians or, increasingly, to music hobbyists with disposable incomes.

There is even evidence that old-fashioned studios and studio roles have actually grown (albeit in small amounts) since 2004-05, fueled by the need for complex scoring sessions on sophisticated video games and big-budget television shows.

The US Census keeps records on industry employment information through the yearly Statistics of United States Businesses Survey. There is a lucky NAICS classification, #512240, that contains sound recording and mastering studios and almost nothing else.

Check out how precipitously employment dropped once DAWs became affordable.

But, the number of studios has steadily increased since then, and the ratio of small studios to large studios has grown.

<img style="width: 600px; display: block; margin-left: auto; margin-right: auto;" src="http://cdn2.hubspot.net/hubfs/316692/studios_copy.jpg&quot; width="800"

There is also this tantalizing chart that appears to show the incomes of sound recording studio employees steadily rising. In 2012 the payroll per employee was the highest it has been in more than a decade.

Because the SUSB survey for this code doesn’t tell us about every economic activity that involves sound recording and mastering, I can only say this information suggests the financial condition of existing recording studios isn’t getting any worse—which is still a much better prognosis than the stories of persistent deterioration and oblivion I’ve heard repeated by some.

We probably don’t get a good picture of the employment levels or incomes of freelance engineers who do not own their own studio. We don’t know to what extent musicians who are professional artists on paper are charging or paying for recording services under the table or as favors. And we can’t peer into the dark recesses of the hobbyist market.

And this last one, the hobbyist market, may be the biggest one of all.

Sparkling new pre-amps and rack processors show up at NAMM year after year. Someone’s buying them. Right?

“The lower end of the market, the base of the pyramid, has greatly expanded as the recording medium changed from tape machines to computer-based digital recording,” says EveAnna Manley, founder of Manley Laboratories, Inc. who helped me understand the new demographics of the end-user market for studio recording gear, which give a different perspective on the resilience of recording as a profession and pastime than the SUSB surveys do.

A few members of the RF Venue team witnessed these changing market dynamics while building Crowley & Tripp microphones.

Former Crowley & Tripp Product Manager and current RF Venue CEO Chris Regan commented, “overall, we saw the demand for the highest end studio gear ceding ground to the middle and lower end of the market. There is still a strong desire for quality tools to capture and record, they just don’t go into multi-million dollar facilities.”

Though C & T was as successful as any maker of ribbon microphones can hope to be, they watched as other high end gear manufacturers and retailers lost margins and went out of business.

So it’s great to hear manufacturers like Manley are doing well, even if many of their awesome tube amps vanish into garage and basement studios, never to be seen (or heard from) ever again.

“While we still supply recording gear to traditional recording and mastering studios, film scoring stages, live sound touring rigs, and working recording engineers,” EveAnna continued, “the market that has really opened up in the last decade or so has been to the songwriter and the hobbyist who have set up DAW-based recording rigs at home.”

How much has the hobbyist market expanded? And what percentage of all studio equipment manufactured do hobbyists buy?

The wireless audio market does not allow me to answer these questions, though it does let me sit at a desk in a city and blog.

As for Tony, he lives out in the sunny hills of Greenfield, steadily building a small but sustainable musical universe that includes a studio. I’d say he’s living the dream.

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

Visualizing Directional and Nearfield Antennas in Central Park

//fast.wistia.net/embed/iframe/459s2sc0it//fast.wistia.net/assets/external/E-v1.js

To compare the effects of two different types of antennas (and the effectiveness of the RF Spotlight at reducing sources of interference), we traveled to New York City in search of something most professionals avoid: crowded spectrum.

We brought a camera, a wireless mic, and some other equipment and camped around 59th and 6th, just inside Central Park.

A passive coax switch fed one RF Spotlight and one CP Beam to a spectrum analyzer. The switch and analyzer let us visualize and compare what a wireless microphone receiver would “see” if either of these two antennas were attached at this location.

With the CP Beam, the signals and noise floor within the antenna’s pattern are amplified (under normal circumstances, a good thing if pointed at mic transmitters). With the Spotlight, the noise floor melts away, leaving nothing but signal, loud and sweet.

The unique radiation pattern of the Spotlight creates a “bubble” (as we often say) of coverage that envelopes proximate transmitters while attenuating competing RF outside its boundaries, resulting in vastly improved signal-to-noise ratio.

What We Learned From Our 2015 Survey

Last week, we sent a survey to RF Venue customers and Audio Gloss subscribers. Nearly a thousand people responded—far more than we expected—with all kinds of interesting information on how wireless audio devices are being used in 2015.

We came away with a much better picture of our customers, and of wireless audio users as a whole. We want to share some of what we found with readers.

The survey went to audio and A/V professionals who work regularly with wireless microphones, or who have an interest in wireless audio products, including our dealer network, and other partners who have purchased RF Venue antennas and RF distribution equipment direct from the factory.

Our customers are over-represented by A/V dealers, wireless audio “power users,” broadcast professionals, and system integrators, so we also sent it to our diverse audience of blog subscribers, most of whom have never purchased from RF Venue.

The first surprise was the ubiquity of in-ear monitors. About 83% of respondents said they work with IEMs.

This confirmed what we already knew, that in-ears have grown more popular in recent years, but we didn’t realize just how popular. It wasn’t long ago that IEMs pretty much lived on major tours. Today, local bands, small to mid-sized churches, and even pubs and small venues are upgrading from wedges to in-ears, or going straight from no monitoring to in-ears. Churches have really helped drive growth in the IEM market with contemporary worship styles that put lots of musicians up on stage every week in concert-like environments.

Aside from general device usage, participants also chose which of six wireless audio brands (AKG, Audio Technica, Lectrosonics, Sennheiser, Shure, and “other”) they use most frequently. Then, we asked which specific models of both mics and IEMs they use within that brand. Most professionals work with, sell, or specify a variety of different models (not just one), so we allowed respondents to choose multiple models.

Analyzing the multiple choice picklist gave us a fascinating look at the mixture of wireless audio technologies in use by our sample, as of this publication.

Some models were far more common than others. Here are the two most popular models by manufacturer.

We also learned what percentage of our sample uses digital modulation and in what frequency band.

39% of all respondents said they use at least one model of digital wireless microphone, with big differences in digital use by band and by brand.

The vast majority of digital systems reported were UHF: 36% of all respondents chose a digital microphone operating in the UHF band (470-698 MHz), with ULX-D accounting for the lion’s share. Only 8% said they use 2.4 GHz band systems. Even fewer picked digital systems using DECT (1.9 GHz) and 900 MHz band frequencies, 7% and 3%, respectively (We did not include intercom manufacturers in this survey, which might have bumped the 2.4 GHz and 900 MHz numbers up).

While we learned what percentage of our sample uses digital microphones, we still don’t know exactly how many digital microphones are out there. In September of last year we conducted a small poll of five large A/V retailers and distributors on digital mic sales by volume. We asked each to roughly estimate what percentage of systems they sold was digital, and how many existing legacy systems they thought were digital. The ballpark estimate was that 25% of systems sold today were digital, and 2-10% of existing systems (which actually gets us pretty close to the number we uncovered last week, but far from hard numbers).

Likewise, there may not be a correlation between a particular microphone model and how many microphones of one model are used or sold by a respondent.

For example, of those who said they use or sell Shure, about 70% said they use the top of the line UHF-R, more than any other model. Only ~30% of respondents said they use the more economical SLX. Does that mean by volume UHF-R outsells SLX by more than 100%? Probably not across the entire market, but within the context of RF Venue customers and Audio Gloss subscribers, who are disproportionately represented by wireless power users, possibly…

But back to digital. 38% is the average rate across all respondents. If we drill down into respondents by manufacturer, the rates of digital adoption are quite different from manufacturer to manufacturer. Of those who use Shure as their primary brand, 68% use one or more digital models, but of those who use Lectrosonics as their primary brand, not a single respondent selected a digital model.

These percentages don’t necessarily mean that customers of one brand dislike the digital mics of that brand. They probably instead reflect the fact that some manufacturers have a lot more digital offerings than others. Shure offers a wide range of digitally modulated microphones, while Lectrosonics offers almost none.

Either way, we learned the wireless audio market is changing—fast—and that wireless audio users are diverse, adaptable, and intelligent.

Thanks to all who participated!

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

All About IFBs

IFBs play a small but important role in the world of wireless audio and pro sound, but are seldom found outside of the broadcast and film community.

Since they are unfamiliar to most, I thought it would be useful to write an informational piece about these systems, for the curious.

In short, IFBs are one-way program audio feeds that can also deliver cues to talent. If you’ve ever seen a news anchor reach up to listen to his/her earphone, you’ve seen an IFB in action.

IFB stands for “interruptible foldback.”

“IFB is a broadcast term that encompasses three things,” explains Michael Brown, East Coast Regional Sales Manager at RTS. “One, a single or many talents hear one-way audio in an earpiece. Two, what the talent hears is some sort of program, which we call the ‘listen source.’ Three, someone (a producer, director, or audio control) can interrupt the listen source with a talent cue.”

An IFB is not so much a single device or system as it is a way of configuring comm systems and mixers to provide discreet in-ear program audio and cues to on-screen talent or off-screen crew.

The content of the program can be nearly anything related to the production—a local program (like a TV show or news), a remote program, cues, music, countdowns, even dead air.

What distinguishes an IFB from a simple one-way feed is the ability of a producer or director to “interrupt” the feed to deliver information to the talent and then “fold back” the program to that talent, as when a producer informs a news anchor of breaking news.

A typical setup is to dedicate one intercom channel for one-way communications with talent who wear translucent or miniature earpieces without headsets. Whenever the person in charge of the IFB transmit station is not speaking, program audio is patched into the feed. Though, configurations differ considerably from application to application, and it is possible to assemble an IFB out of different kinds of equipment.

For example, the link between IFB control station and talent may be wireless, or wired. The producer and talent may be in the same studio, or they can be hundreds of miles apart with the feed delivered via satellite or PL line. IFB systems may be set up to allow one or more producers to patch multiple program feeds to multiple talents or crew, as is sometimes necessary for large-scale productions and major network operations.

On film sets, IFBs usually supply production audio from the sound cart to members of the crew, who may be dispersed across a set. Producers and directors can interrupt the mix to deliver instructions to the crew or, less commonly, to cue talent as well.

Film crew member with IFB earpiece.

Products sold as “wireless IFBs” are analogous to a monoaural in-ear monitor transmitter (an FM transmitter with an XLR audio input), a beltpack receiver, and an earpiece. They do not include the comm system interrupt or IFB control panel, and must be properly integrated with mixers and intercoms to become functional IFBs for cueing.

Many wireless IFB systems are unusual in that they operate in the VHF range. Some of them in the deep water of low band VHF, roughly between 54-88 MHz, like the RTS TT-16 and Comtek 72-76 MHz series (to the best of my knowledge IFBs are the only wireless audio devices that use frequencies in low band VHF). Such low frequencies give these systems very long range. Others, like the Lectrosonics IFB and Clear-Com PTX/PRC use the more familiar UHF band, between 470-698 MHz.

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

What is Squelch?

Wireless microphones are designed with squelch circuits to mute audio when the receiver loses or cannot find the transmitter’s signal. Squelch circuits are necessary because receivers (especially analog ones) try and demodulate anything they can, including waves that make up the noise floor and interfering signals. In the absence of squelch, receivers would send a hellish, screeching static into the PA during dropouts or when the transmitters were off—possibly destroying speakers along with the tympanic membranes of everyone in the audience.

There are different methods of squelching noise, and most receivers offer the opportunity to adjust the squelch setting in some way, although for the average user no adjustment is usually necessary.

The simplest mutes the audio if the RF signal strength drops below a certain level. This works relatively well, but is far from fool-proof. Such a circuit does not consider any characteristic of the signal other than strength, and can be tricked into opening audio on noise signals that are above the threshold. This type of squelch gets more reliable the higher the threshold is set, but sacrifices operating range for reliability.

Most modern receivers determine squelch using more intelligent methods.

One is to evaluate the frequency of the audio in the demodulated signal. Since a signal arriving from a microphone will not include any high frequencies, if the receiver detects anything above 16-20 kHz, it will assume the incoming RF is noise, not signal, and squelch it out.

Another is to include an audio “tone key” in the transmitted signal that is either above or below audible range. The receiver will squelch when it cannot locate the tone key. A tone key squelch can be fooled by rogue harmonics that approximate the tone key’s frequency or by other nearby microphone transmitters (used by someone other than you) that are also using tone keys.

In practice wireless systems may use a combination of these techniques and, overall, they do a very good job at muting noise without any input from the user. Gone are the days when squelch needed constant attention and noise seemed like just another part of the job.

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

Don’t Forget to Gain Stage Your Transmitter

Gain staging wireless microphones is an important but overlooked step in getting wireless systems to sound their best. James Stoffo touched on gain staging briefly during his presentation with T.C. Furlong this week in Chicago, which we had the pleasure of attending. Since improper transmitter gain staging causes audio distortion and sometimes RF trouble, I think the subject is important enough to expand on here.

How to gain stage a transmitter.

Gain staging is manually setting audio gain on a wireless microphone to the correct level. This type of gain is referred to as “transmitter gain” because of where the gain is applied in the signal chain: after the mic audio input and before RF modulation occurs in the transmitter. Wireless microphone handhelds and body packs combine a microphone and a radio transmitter. We are talking about setting gain in a stage inside the microphone itself, rather than manipulating the gain of the resulting signal at a later part in the chain.

On microphone models which support it, setting transmitter gain is a simple procedure performed either with a mechanical switch or knob on the transmitter or within the software interface on the beltpack/handheld or receiver. The exact method will vary from model to model.

Once you’ve consulted your microphone’s manual on setting transmitter gain (keep a lookout for terminology confusion as described below), have the performer use the microphone with his or her normal speaking or singing volume. Monitor the audio level meter on the receiver, not the RF level on the receiver.

RF meter vs. audio meter on ULX-D. There are no bars on the audio meter because I am not speaking into the mic, but you can see the “OL” overload peak marking.

The audio level should jump around just underneath the peak indicator without crossing it. If the audio peaks, turn down the gain. If the levels are low (only a few bars), turn up the gain. Transmitter gain should be adjusted and returned to the performer iteratively until a “sweet spot” is reached where the audio meter reads well above its lowest display, but doesn’t peak.

Audio meters on microphones vary across makes and models. Some have a more nuanced and sensitive display, like the Shure UHF-R, whose manual suggests setting transmitter gain so peaks never exceed the yellow range. Less expensive models do not have a “yellow” or caution zone, so it is more difficult to accurately dial in transmitter gain.

If transmitter gain is set too low, like when a performer is soft-spoken, the audio’s signal-to-noise ratio (SNR) will be low, and the full dynamic range of the system will be lost. This pitfall should be familiar to mixers and sound engineers who carefully manage gain structure, but they may not always realize that in a wireless audio system gain management must begin at the transmitter.

Transmitter gain set too low for performer’s volume.

Transmitter gain set too high, causing overmodulation and distortion.

Transmitter gain set correctly for this particular performer to maximize SNR (-0 dB is arbitrary, the gain setting depends on the performer’s volume).

If audio gain at the transmitter is set too high, audio clipping and distortion will occur, but not necessarily because the audio SNR ceiling is exceeded. The bigger concern is over modulation of RF. It’s a bit counterintuitive, but setting audio gain at the transmitter too high results in an RF problem, which in turn manifests as audible distortion.

Over modulation is a topic unto itself, but in short, over modulation is when the wireless carrier frequency in a frequency modulated (FM) system exceeds the maximum deviation of the system.

With FM modulation, the amount of deviation around a center or “rest” frequency is proportional to the audio signal’s amplitude. When audio is fed into the microphone, the carrier moves up and down around the center, or “deviates,” according to the amplitude of the audio wave.

Wireless microphone receivers aren’t very good at recovering audio from FM signals that deviate above and below a center frequency by their pre-determined amount.

High transmitter gain can cause over modulation problems in other parts of the signal chain before the RF modulator (like an A/D) which also result in audio distortion. Some mics include limiters before the RF stages to make carrier over modulation unlikely, though audio distortion is still possible.

Terminology confusion.

Setting the audio gain of a transmitter, or “transmitter gain” as it is usually described in manuals, refers to gain applied to the audio signal before the audio is modulated inside the transmitter. Transmitter gain may be thought of as a single, virtual fader for the audio signal coming from the microphone, used to compensate for differences in volume from one performer to the next.

A block diagram of typical components included inside a wireless microphone handheld or bodypack transmitter.

Transmitter gain is not the same thing as transmitter output power. Transmitter output power refers to the RF (not audio) power that a transmitter uses to send signal through the air. This is measured in milliwatts, and is commonly adjustable in some increment of 10 mW between 10 mW and 50 mW, if it is adjustable at all. Adjusting transmitter audio gain will not change transmitter RF output power, and vice versa.

“Gain” may be used colloquially and in manuals to refer to a few other parameters within a wireless microphone system. Make sure the transmitter gain you set is actually transmitter gain, instead of any of the following three settings:

Input RF attenuation, which may be inaccurately described as “input gain,” is RF padding at the front end of the receiver or distributor used to attenuate strong incoming RF signals. This setting may be within the software interface or as a mechanical dip switch, and is described as either negative dB, or number of dB of attenuation. These settings are very useful for receivers suffering from overloaded RF, but will not fix over modulation when the transmitter gain is set too high. RF attenuation settings are also easy to forget once they are enabled, or if they arrive in the “on” position from a factory or rental house. Always make sure to double check these settings are off.

Input sensitivity is available on some transmitters. This is closely related to transmitter gain, usually located before transmitter gain. It is analogous to the “trim” function on a mixer and is used to accommodate difference in input levels from different types of microphone elements.

Output gain/level or mic/line output is the adjustment of audio gain after the receiver has demodulated RF but before the XLR or ¼” output to the mixer or PA. Output gain is used to manage audio gain structure and return the output to line level or mic level ahead of mixers, speakers, processing racks, etc. The popular Sennheiser EW G3 mics refer to this as “AF out”.

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

Insights received via email from Steve Caldwell of Norwest, posted here in italics until we get our comment system up and running…

One thing that I have found becoming more commonplace is the poor practice of setting radio microphone transmitter audio gain by using the meters on a mixing desk, rather than looking at the meters on the receiver. Even if some attempt has been made to calibrate the meters on the desk to the apparent level on the receiver, on most receivers the level indicated on the receiver is not linear with frequency.

This only occurs with analog radio microphones of course, but it is due to the Emphasis noise reduction systems used in Analog FM transmission, and the fact that the audio meters on the receiver are INSIDE the Emphasis loop. As you may be aware, A Pre-emphasis filter is applied to the audio before transmission, and then a de-emphasis filter is applied in the receiver after demodulation. A bit similar to the old Dolby Noise Reduction techniques. Because there is the ability for over modulation to occur more easily at higher frequencies (due to the pre-emphasising of the audio before transmission), the meters on the receiver reflect the DEVIATION occurring in the FM, not the actual resultant audio after de-emphasis.

This means that most meters on an analog receiver will be more sensitive at higher frequencies (and respond more to sibilance, etc), than at lower frequencies. A meter connected to the audio output of a receiver (such as at the mixing desk), is after de-emphasis, and as such does not represent the actual FM modulation level. The meters at the receiver should ALWAYS be referenced when making gain adjustments, so as not to allow over modulation at higher frequencies. Consulting the meters on a desk is only really usefull in reference terms.

Steve

PS: I should also mention, it is my understanding that in order to get spectrum authority (FCC or whoever) compliance, the transmitters must use a mechanism to avoid over modulation of the RF signal. This is normally done in the form of a limiter in the audio stage before the audio is modulated in the PLL loop filter. So it’s actually very difficult to over modulate a transmitter, from an RF point of view. From an audio point of view hitting this limiter is not going to do you any favours.