WASHINGTON, DC – Okay, just a forewarning. There will be a significant amount of conjecture and opinion here…First, the actual decision. Wireless mics, instrument packs and IEMs are covered under Part 15 – at least those systems under 50 Milliwatts. There are also commercial systems capable of much higher power, and those still require a license.)
Back to what the Part 15 thing means in a moment…
Pro audio did not walk away with a total loss. The FCC agreed to put aside two UHF TV channels of bandwidth in every city specifically for wireless mics. It appears that these spaces may change slightly from city to city based on what spectrum is currently being used there. Generally, these will cluster around channel 37, which is reserved for radio telescopes.
So let's bottom-line this. A UHF TV "channel" consists of about 6 MHz of bandwidth. And two of those are reserved in each city. Using current analog technology, we can squeeze 12 to 16 channels of wireless into that space. That's for the total space provided by both channels. Remember, stereo IEMs take about 40 percent more bandwidth, so probably 10 IEMs max. And to quote wireless guru Henry Cohen, the issue becomes one of having a relatively high power transmit antenna near a wireless mic/com receiver antenna and desensing the receiver. This means physical separation of antennas, or external bandpass filtering, is just as important as frequency separation.
That number might work fine in BF, Egypt, but – to use an example that I have worked and know pretty well – in, say, downtown Las Vegas, where there may be four to six bands playing on the same block and sometimes in the same building, this can get tricky.
This is where we get back to the guts of the Part 15 thing again. Just by virtue of being bound by the rules of Part 15, we give tacit agreement to accept interference from other Part 15 devices. Actually, as Henry pointed out, it is not tacit approval, it is a regulatory condition of operating these devices. Yes, that means what you think it does. If your show and the one next door are stepping on each other's wireless, there is no one for you to go to and get them to intervene.
Next issue. While most pro wireless units give you 100 or more frequencies from which to choose, they are between a set pair of upper and lower frequencies. For example, I am looking at a stereo IEM transmitter that is on my desk right now. It offers 100 frequency choices. But all of those choices lie between 614 and 647 MHz. So what if they set aside channels for my area do not fall in that range? Well, unless someone sets up some kind of trading apparatus (and that could include the manufacturers themselves), then your choices are to sell it on eBay or SoundBroker.com, leave it at the shop, or take your chances on wireless hits from other devices.
Lest we forget that pro audio is not really a part of the greater consumer electronics industry, note that EVERYWHERE outside of the industry, this is seen as a major win for commerce and consumers. This, from CNET, on the day the ruling was announced:
"As part of the new rules adopted today, the FCC agreed to set aside two channels for wireless microphone use to mitigate potential interference issues. But the commission said it would not require device makers to include geolocation spectrum sensing technology in new devices to ensure that these products don't interfere with existing services already using the spectrum. This is a key win for device makers, because it means that they do not have to include the potentially expensive technology in their products. Instead, devices will query a special geolocation database that makes sure no one is using that spectrum before it transmits. This database check is largely to prevent white space services from interfering with broadcast TV signals.
For those of you who have not followed this, or need a refresher, consumer electronics and Internet service providers have been trying to get this spectrum for a new generation of handheld wireless devices like, say, the iPad, but without the 3G cellular connection. You know how there are Internet "hot spots" in lots of businesses? Those currently use the 2.4 GHz band, which is controlled by international agreements and is non-licensed. But as you know if you have a wireless router in your home or office, the range is limited and coverage can be spotty.
But when it comes to wireless, smaller numbers are better. A signal in the 500-700 MHz range has a much longer waveform than one in the 2.4 GHz range, and longer waves travel farther and go through obstacles like walls much better. So, getting all of those hot spots to move to 500 MHz routers could potentially create a citywide hotspot that anyone could access. It can also be used to provide wireless access to remote and rural areas where running a cable is not practical. So there are a lot of good things that will come out of this. Just not good for those of us in pro audio.
To quote Don Boomer, who heads up the digital wireless effort for Line 6, "The FCC sees that another batch of unlicensed frequencies will offer economic development and provide the country with a new super Wi-Fi. Ever since the Balanced Budget Amendment of 1997 and, more recently, the proposed National Broadband Plan, it is apparent that the core TV band will be in relative chaos for the near future."
We'll be including the official word from a number of manufacturers in the upcoming October issue of FOH. The current approaches from the two biggest wireless makers (Sennheiser and Shure) include slicing the available bandwidth into smaller chunks and working to minimize intermodulation distortion, and also offering units with much larger bandwidth in terms of available frequencies – in some cases, units that cover the entire UHF spectrum.
But, Don has it right. This spectrum is going to be fought over for the foreseeable future, and when the pro audio biz goes up against the Microsoft/Google/HPs of the world, we are going to come up short every time. As is usually the case, the solution will be technological, and like so much in our live audio world, the future is probably digital.
Also in the October issue of FOH, be looking for Steve LaCerra's On the Digital Edge column, where he'll provide a rundown of the available digital stuff right now. We're also planning a Road Test feature on latest Line 6 digital wireless mic.
But we should emphasize that AKG, Lectrosonics and Line 6 all offer digital wireless for live performance right now. The advantage of digital is that, because the A-to-D conversion happens in the mic or beltpack, you are no longer transmitting audio. You are transmitting data. And when it comes to data, it can be error-corrected.
As Henry pointed out to me, digital does not solve the basic problems inherent in any RF system, nor is it immune to interference. Also, error correction means processing time, and that means latency – the constant thorn in the side in digital audio.
I have a little device called a JamLink that converts audio to digital and transmits between two devices via the Internet, and I have used it with a band in Las Vegas and a singer in Cali, and it worked. There was just enough latency to make it annoying, but not enough to make it unusable. That amount of latency was acceptable in a rehearsal situation, but would have been a disaster in an actual performance. But that level of latency was due to a host of factors, including a less-than-perfect setup, a less-than-ideal upload/download speed, and distance – the two groups were separated by a good 250 miles.
In a performance situation, digital wireless audio can work kind of like the Internet itself does on a much smaller scale. Because the transmission is data, multiple versions of it can be sent over different frequencies and put back together at the receiver before the D-to-A conversion. So if your data takes a hit on one frequency, the processor in the receiver says, "Oops, there's a glitch. I'm gonna grab that data from this stream over here, where it is undamaged." And what comes out sounds like a continuous audio signal. But again. What level of latency is okay for your gig?
So where do we end up for now? The devices that will eventually cause us problems are not even on the market yet. But I fully expect to see first-generation versions at the Consumer Electronics Show in January. and to see them in use by, probably, April of 2011. We have the two channels that have been set aside, and the spectrum between channels 14 and 21 will remain off limits to these devices as well, although we will still have to wedge our way into the holes in that space. So the sky is not falling today. There are a lot of smart people developing products in this industry, and ways will be found around this. But for now? Hang on, it's gonna be a rough ride.
