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A Look at the Zaxcom TRX742 Plug-On Transmitter

As purists often do, we who have stubbornly insisted on a hardwired boom must finally admit defeat: What started as a novel party trick called “Wireless Boom” is now the rule. On production stages where a hand-held boom is used, the boom mic is much more likely to be wireless than hardwired. The old-school side of the debate was an honorable one because the hardwired mic gave us higher quality sound: far less noise, no companding, no harsh limiting… just the mic’s high fidelity signal. But as the quality of wireless systems gradually improved, more and more sound departments have come to think of the cable as an unnecessary evil. The good news is that there’s no need to sulk: We, the purists, the guardians of high standards, the stubborn holdouts, now have a way to join the winning side with dignity…

Zaxcom is well known for the high quality sound of their pure-digital wireless mic systems. While there are some competing brands with digital systems on the fringes that may eventually need to be considered, Zaxcom is currently the only significant player. In the interest of full disclosure, I’ll point out that when comparing the range-before-dropout performance of this 125mW Zaxcom digital system with a 250mW analog system from a respected competitor, the digital system’s range was about 10% less than the analog system, which is consistent with my other digital vs analog wireless comparisons over the years. But it’s important to also point out that the criteria for determining the best wireless mic system is very subjective, and a personal balance of sonic quality, range, reliability, size, and other features. The range of the Zaxcom TRX742 system is well within the needs of most productions, and when the goal is to have the wireless boom sound as much like a hard-wired mic as possible, Zaxcom is the clear leader. While the Zaxcom TRX742 plug-on transmitter can turn any mic that has a 3-pin or 5-pin XLR connector into a wireless simply by plugging it on, the most challenging use for a wireless system is the boom mic for dramatic dialog. So this review will be limited to the wireless boom.

Zaxcom has added versatility to the TRX742 transmitter with changeable XLR input adapters, which Zaxcom calls “cones”. There is a 3-pin cone for standard microphones (48V phantom), a 5-pin cone for stereo microphones (48V phantom), and 3-pin digital cones for both AES-3 and AES-42 microphones (10V phantom). With their new “NeverClip” technology included in the new TRX742, Zaxcom pulls even further ahead in this digital one horse race.

Just a few bits about NeverClip (four bits, actually)

NeverClip is Zaxcom’s patent pending technology that gives an additional 20dB of headroom before exceeding digital max. It does this by using two A-D converters, where the second one seamlessly takes over just before the first one reaches maximum, making use of the four traditionally unused bits, giving a theoretical (and claimed) dynamic range of 137dB, which is more than most microphones have. This means, with the gain properly set, the microphone will actually overload before the transmitter does. Thought of another way: NeverClip devices’ input can be set up to 20dB lower than we are used to, without adding noise, which means that a NeverClip device such as the TRX742 does not need input limiting any more than does the microphone itself. (There is more to discuss about NeverClip, and its place in the complete production-to-postproduction chain, but we’ll keep this piece focused on the TRX742).

Because Zaxcom’s transmitters actually send a digital data stream through the air, they are able to handle two discrete channels of audio with a single transmitter and receiver. Imagine how easy it will be to get stereo effects and ambience by putting a stereo mic on one end of a boom pole and plugging in a single transmitter at the base. This, alone, makes the TRX742 uniquely valuable, even without considering that it is also a self-contained, high-quality, timecode, 2-channel recorder. Recording capability is in all Zaxcom transmitters, and has already been reviewed many times, so we’ll stick to just the transmitter part this time.

I’ve used wireless mics about as much as anyone over the last 35 years, in the full range of film and video production types, and am familiar with about every change and advancement made over those years. Because of that, a lot of people depend on my assessment of wireless sound equipment they choose or choose not to invest in, and I can neither afford to have them misled nor miss out. So I set out to expose the Zaxcom TRX742 for what it really is.

I had the TRX742 and QRX100 receiver during the same week that I had two days on the ABC series Nashville. (The fulltime mixer is Joe Foglia. I am the mixer on the “double-up days” and reshoots, about three days each month.). On this show I typically use a wireless system for the primary boom, and hardwire the second boom.

Before putting the TRX742 to work on a real production, I spent some time with it with boom operator, Kevin Cerchiai. It is surprisingly light-weight, even with three lithium AA batteries. Kevin mentioned that it was light enough that he could use it on the mic end of the pole if needed for extra range. Granted, the mic end of the pole is not where you want the additional weight of a transmitter, but keep in mind that doing so would allow the pole’s internal coiled cable to be removed, which weighs more than the transmitter. The look and feel of the build quality is actually very nice, and shows a continued trend toward refinement on the part of Zaxcom. One point to pick on would be the battery door (but nearly all battery doors get picked on). It hinges on one end and is held closed with two strong rare-earth magnets on the other end, making for an easy one-handed operation. However, Kevin noticed that it could be accidentally jarred open a little easier than it should, so for peace of mind he secured it with tape. There seems to be room for installing another pair of small magnets, which I think would take care of the issue, and Zaxcom is looking into this possibility. We continued going through the options and settings, conducting walk-tests for range, etc., all of which seemed fine. But, as all production sound crews know, the conditions we encounter on the set can only be duplicated on the set, with real actors, and only after “Action!” has been called.

Both days with the TRX742 were on sound stage. The first thing we did was to walk the stage for a range test, and the Zaxcom system covered entire stage without dropouts. The first scene was a typical interior dining table set, with two actors whispering as they are prone to do these days. With levels set during rehearsal, the Zaxcom TRX742 showed its true colors on the first take: After a few lines of quiet dialog, one of the actors gave a laugh that was SUDDENLY VERY LOUD. During the milliseconds this was happening, my brain automatically prepared itself for the sound that would surely result: The crunch of digital overload and/or the squash of a transmitter’s brick-wall limiter. But it didn’t happen. The yell was loud, but just as clear and natural as the words before and after. In this situation of extremes – extreme low levels suddenly followed by extreme high levels – the Sennheiser MKH-8050 microphone behaved exactly like the same mic wired directly to my mixing console: No detectable additional noise, no clipping, no distortion, no limiting, and with all the clarity.

The performance of any professional audio device is somewhat dependent on the user-adjustable gain structure, which is usually a challenge for wireless mic transmitters because they are away from the person doing the mixing. But the TRX742, like other Zaxcom transmitters, has the ability to have its gain settings adjusted by the person at the mixer, using a Zaxcom IFB transmitter. With this system, the transmitter gain is actually adjusted as if it were the mixer’s input trim, as it should be.

Since we had only two days of production with the TRX742, and couldn’t risk having the transmitter batteries go flat, I have no battery-life statistics to report other than to say that we changed the three lithium AA batteries after lunch because the internal meter seemed to suggest it, and the battery change got us through the rest of the 14 hour day. Keep in mind that we turned off the transmitter whenever it was practical to do so, which could easily account for half of that time.

So, the Zaxcom TRX742 plug-on pure digital transmitter is nicely made, lightweight, usually has plenty of range, and accepts mono, stereo, and digital microphones, has a built-in recorder, can be controlled remotely, and has 137dB of dynamic range.

As you might expect all of these premium features come at a bit of a premium price: U.S. $1995 for the transmitter and one cone (additional cones $200). But is it worth it? I’m sure that many will say “yes,” and put their money where their ears are. As purists often do.

(Credit Sound and Picture)


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