sound for film & video

Mission Critical with Zaxcom

The sounds of surgery at Children’s Hospital

You think you struggle with technology? Buddy, you don’t know what technology really is until you’ve seen a major surgical procedure. Figuring out how to sync your smartphone is nothing compared to the kinds of devices you need to know how to operate if you’re going to install a pair of expandable titanium rods in a 10 year-old’s back.

But that’s getting a little ahead of the story. This post is about some new audio technology that’s still mighty impressive when kept in proper perspective.

Ever since Talamas demonstrated the hot-shot capacities of Zaxcom’s wireless systems I’ve been quite keen for a project that called for the major firepower it provides. My good friend, DP, and producer Robert Pierce provided the opportunity: the anesthesiology department at Children’s Hospital was going to a big conference in Brazil, and they hired Robert to document one of their surgeries. Good clean capture of the dialog and interplay between the members of the surgical team would be the goal.

Among the challenges this one presented were (a) making absolutely sure our gear would not create any interference with the medical equipment in the operating room, (b) vice versa, (c) not being able to directly touch any belt pack transmitters once they were placed on the surgical team (a nurse who knew sterile procedures would be the only person who could wrangle the lavs once people were in the O.R.) and (d) extremely little control over how or when things happened. There was going to be no opportunity to fumble with menus on the transmitters for at least five straight hours. And there were not going to be any retakes either, natch. In short: get it right from the beginning or don’t get it at all.

Fortunately we now live in a world where field recording is a hell of a lot more sophisticated than a microphone on the end of a stick. There are quite a few things Zaxcom’s line-up can do that I knew would perfectly address the challenges at hand:

  • Recording at the beltpack: each transmitter holds a microSD card that records the audio before it hits the radio transmitter. No matter how bad any RF interference got, we’d still have a clean recording to fall back on. And those recordings would be time stamped for easy sync should we need them.
  • Remote frequency change: dial up a different frequency on the receiver and within a second the transmitter pack will follow suit. Should the X-37 space modulator suddenly be wheeled into the room to take X, Y, or Z-rays, and my carefully selected frequencies be thrown into disarray, I’d be able to rescan on the fly without having to go in the operating room, never mind touching the packs directly.
  • Remote gain change: since the on-pack card is recording the capsule directly, one needs to be able to manipulate the gain of the mic at the belt pack. Zaxcom lets you manipulate that gain from the receivers.
  • Remote battery status report: a display on receiver gives accurate reports of the remaining battery life. No guessing as to when the rebats would be, no waiting for the signal to crap out.

What makes a lot of the above possible is “ZaxNet”, a separate audio and metadata signal that operates roughly in the 2.4 G range. ZaxNet is how the timecode would get to the on-transmitter record cards, and how the transmitters would be able to respond to the remote commands. It also provides IFB capacities, either through small blocks that strap to the transmitters or dedicated belt packs. And although we didn’t wind up using it, we could have remotely taken the transmitters in and out of a low-power state to conserve battery life (you gotta love a product that has a line in the manual reading, “This feature was created for the NFL…”), as well as controlled the record and playback transports of each belt pack individually.

What more could you wish for? Well, remote battery change would be something, but until we know more about how to break the laws of physics we’ll just have to keep that one on the Christmas list.


The good folks at Talamas have been treating me well for years, and this time they came through better than ever. A few days ahead of the shoot they let me take away their new Fusion recorder, four belt pack recorders/transmitters, and three QRX100 receivers with ZaxNet capacities for a thorough tech-through. It was a good thing, because when you’ve got this much capacity and this many possible configurations at your fingertips, you’ve also got a bit of a learning curve. (For whatever its limitations, there’s an operational simplicity to a mic on the end of a stick that can be quite attractive.)

After a few bumps in the road, lots of manual reading, a fair amount of rotating through menus, and a couple of phone calls, I had in front of me a system that would record four wireless lavs, two stationary, wired overhead mics, and a stereo-pair reference mix on the Fusion. The stereo mix would be so the editor could get to work on selecting shots with minimal audio alignment and mix fuss. At the same time the belt packs would be recording fail-safe files, time stamped with the same timecode as the Fusion tracks. Timecode would be free-run time-of-day. The two video cameras would jam sync throughout the day. We chose to let the camera audio use the built-in mics, both for extra audio coverage, and to allow the photographers to roam without encumbrance.

The day before the surgery was a long day of following the young patient on his pre-operative procedures and interviewing members of the staff using a fairly normal documentary style (mic at the end of a stick on one channel, wireless lav on the other). Then we were escorted into the labyrinth of the surgery area at Children’s, given surgical scrubs, and shown the way to Operating Room 24. (Yes, they have that many and more, and most of them seemed to be in use.)

Our first task was to string up the wired mics, a reasonably simple endeavor. They were the ultimate fail-safe, in case we ran into a situation where either there was too much interference for our wireless audio to be usable, or if the hospital technicians determined we needed to disable RF transmission because it was interfering with the medical equipment. Thankfully neither situation arose, but I discovered that mixing the overheads in low provided a nice stereo ambiance and bit of sonic adhesive to distract from any discontinuities in the main dialog track, while also picking up bits and pieces of the personnel who weren’t laved.

Next came the wireless test. I fired up the four transmitters and used the built-in autoscan feature to find the cleanest frequencies. To my pleasant surprise, the RF conditions in the surgical area seemed to be much cleaner than at my home. (I can only guess this is because the folks who build operating rooms have a good interest in keeping stray RF away.) I then handed all four packs to the surgical support technicians, who waved them around and rubbed them against any and all critical machinery in the operating room. Meanwhile I monitored signal at my bag in the “sub-sterile area” just outside the O.R., where I would be stationed during the actual operation. We discovered no interference in either direction and headed home for a good night’s sleep — call for the next day would be 6:15 A.M.


The next morning, freshly caffeinated and back in our scrubs, we were introduced to the surgical team. We wired the anesthesiologists pretty normally, dressing the lav wires under their scrubs. But the two surgeons had special requirements; because they were working directly in the sterile field, they would be wearing sterile gowns over their normal scrubs. I needed to wire them before they scrubbed up, and then the nurse would move the capsules from the normal scrubs to the outside of the sterile gowns. I gave her a bit of training on how to orient the capsules, showed her how the doors to the battery compartments worked (magnetic! easy!), took up my station, crossed my fingers, and lit the red button on the Fusion.

Everything started off swimmingly, with nice strong signals, clean audio, and no hits. But soon enough I would hear two words that could make the strongest production mixer wince: lead apron. A few things they hadn’t thought to warn us about were (a) the number of times an X-Ray machine would be used (b) the fact that all staff in the O.R. during those times (including the camera guys) would need to be wearing lead aprons, and (c) that the two surgeons would be wearing lead jackets under their sterile gowns during the entire operation, seeing as they would not be able to take them on and off without rescrubbing each time. (And if you think your feet hurt at the end of a long day, imagine being a surgeon standing 5 hours or more straight while wearing a coat of lead.)

At first I thought this might just create some temporary inconvenience during the actual X-ray procedure, but within a few minutes of watching one receiver bounce back and forth between the A and B antennas, it occurred to me that the transmitter for the orthopedic specialist might now be positioned under a layer of lead (they had placed the jackets on the surgeons out of my sight). I thanked my stars and Zaxcom for the belt pack recording cards, and had a nurse move the transmitter to outside the jacket when she got a chance. Signal did improve, but was still a bit erratic, since the lead-encased head surgeon was positioned directly between my station and the the orthopedic specialist, meaning the signal still had two layers of lead to contend with. Fortunately the diversity switching in the Zaxcom system was good enough that I completed the day with no audible hits, despite all the scary red lights and A/B bouncing. The belt pack recording helped me breath easy, but in the end it probably won’t be necessary to crack it open.

Aside from those “interesting” moments, things were reliable and uneventful. While the surgical staff monitored the patient’s vital signs on flat-panel displays in the operating room, I was able to monitor the vital signs of all four transmitters using the two-line LED readouts on the receivers:

In the picture above, the display informs me I’m operating this mic at 668.4 MHz. The arrow indicates antenna A is being used, which corresponds with the signal strength ramps at the right. The “REC” indicates the transmitter is recording audio to its on-board card, and the battery graph lets me know I’ve got about 40 minutes of power left — it will flash when we start to scrape the bottom of the barrel. (The “A” at the left is not related to the antenna – it’s the receiver channel. Each QRX100 is capable of picking up two transmitters. The pictured receiver is set to receive a single transmitter.)

The Zaxcom transmitters come in two styles; the TRX900AA takes a pair of AA batteries which provide operating time of about 4 hours, and the TRX900LT takes a single AA, giving about 2.5 hours. Talamas had two of each available. We chose to put the double-battery packs on the surgeons, since we’d have less access to their packs. As people left the O.R. to take breaks during the 5 hour procedure, we’d grab the chance to switch out to fresh batteries. But the head surgeon stayed in the O.R. the whole time, and when the readout for his transmitter got close to the bottom I gave the nurse the heads-up and she took the first opportunity to drop a fresh pair of batteries into his pack while he was still at the table. In every case the cards on the transmitters re-jammed and went right back to recording without even needing to flip the power switch, confirmed by both the incoming timecode display on the transmitter itself and the “R” on the receiver display.

The Fusion was a joy to operate. The touch-screen meant going through the dozens of menus any modern recording device will present was quick and relatively intuitive. Touching and holding any track meter would solo that track in my cans. The eight rotary pots can be assigned to any point in the signal chain, starting at the belt pack gain stage all the way through to the post-fader mix. One can even assign multiple pots to the same channel for control over different points in the chain, meaning, for example, one pot can remotely control the belt pack gain while another controls the submix. In spite of our brief acquaintance, the Fusion never sent me into any operational black holes. I can honestly say that the whole system worked exactly as advertised, and how many times can we say that about anything nowadays?

As for the actual surgical procedure itself, the entire film crew jokingly noted a similarity to auto repair — there was a fair amount of ratcheting, screwing, drilling, and pushing going on during those five hours, all of which is captured in glorious 24 bit sound from six different perspectives. Every once in a while I’d peek through the window in the O.R. door, note that everyone’s capsule was still in the right place, think to myself, “Yes, that is an awfully long incision,” and retreat back to my bag. How the camera guys managed it I’m not sure.


Back in our street clothes and a bit bedraggled, Robert and I grabbed some good beer and retired to my studio for the bane of our wonderful new digital world: media management. Tape may have had many limitations, but at least it served as its own archive. With digital it’s probably not going to be that simple, and odds are good you’re going to end up needing to suck some bits from one thing onto another. (And depending on the medium it’s probably going to be sooner than later.)

The Fusion records onto a pair of CF cards — the primary records into the proprietary .zax format. The big feature of .zax is that should the unit crash during recording the files can be fully recovered right up the point of the crash, something that isn’t possible with standard audio file formats. The downside is that the .zax files need to go through a bit of conversion utility software in order to become something that can be used in a standard editing tool. The secondary card can be set to either record .zax or the familiar broadcast .wav for immediate delivery directly into an edit workflow. (We chose the second strategy, and it paid off in an unexpected way.) The Fusion can also use an external hard drive as the secondary. The transmitter record cards were microSD, and they recorded solely to .zax.

It’s in that conversion utility that Zaxcom shows its weakness. Unlike the Sound Devices series, the Zaxcom system has a somewhat inscrutable and inconvenient way of going about naming things. Tracks names are logical, and the files from the transmitter cards bear any unique 8 character identifier you want to assign to the packs. But Zaxcom seems fond of something they call “segments”. Yes, you can create and assign take numbers on the Fusion, but they won’t show up in the file names. Instead you’re presented with a list of “segments”, and the numbering of those segments probably won’t have any relationship to your take numbers, nor even the number of times you pressed record — frequently during the recording I noticed that the segment number had incremented unexpectedly. As near as I can tell the .zax format creates a number of “containers” that are then filled up with audio, and when one container gets full, the next one is used and the segment number is incremented. When recording long takes the result can be a single continuous recording being broken up into multiple segments. (Fortunately those segments lined up seamlessly when I spotted them in my audio workstation.) The conversion software creates a .csv report telling you which segments correspond to which take numbers, but I can imagine this would be much less convenient then having the scene and take number just be right there in the file name.

For the files on the transmitter cards, the naming scheme is even more cumbersome: not only do you have segments to contend with (one for each time stopped or re-batted), but every file name starts with eight characters corresponding to the timecode user bits and another six corresponding to the timecode at the start of the file (leaving off the frames). Thus a file will be named something like “01111206_101412_PACK2_004.WAV” I can only imagine this is going to make some poor editor’s eyes swim during a long post session.

Then there was the “slight” problem of “Segment 4” from the Fusion crashing the conversion software every time. (Talamas has forwarded those files to Zaxcom so they can debug.) That’s where the decision to use .wav on the secondary card was lucky, since the files on that card were trouble-free.

In spite of all that convolution (the logical kind, not the reverb kind) the files from both the Fusion and the transmitter packs lined right up flawlessly in my DAW. The transmitter files were well within a frame’s sync (only about 250 samples difference). The next day Robert brought the audio in against the picture, and found it lined up with the on-camera mics to within a frame as well — not bad for an entire day’s worth of harried jam-syncing. For a guy like me who over the years has trained himself to see sync errors down to a frame, it’s paradise. Of course, for this production we had an advantage: all our “actors” were wearing surgical masks. ADR for this one would be a piece of cake!


We’ve not locked down the details yet, but I’m hoping to get the chance to do the post mix as well. At that point I’ll be able to really confirm if the sound quality of Zaxcom’s system is as clean as my first impression. At no time during the recording did I hear any wireless hits, and there was a really nice absence of the thin fuzziness I’ve grown weary of with the some of the more pedestrian systems. But the true test of these things is always the point where you sit down an listen to it for hours against the picture — if you’re still happy late in the day then you’ve got something good. I’ll update the chart here when it happens.

*(Post Anesthesia Care Unit)


4 responses

  1. Jim Wilkens

    Wow. That’s very cool, Ken. Do you think you will use those mics again for for a different type of production?

    February 1, 2012 at 3:16 pm

    • It would depend on the needs and budget of the project. Some of this stuff is overkill for more basic productions (a sit-down interview to video, for example, or a low-budget short film with fairly normal set-ups). But I would not hesitate to use Zaxcom again in any situation where redundancy and high fault-tolerance is needed — a sit-down interview with the President, for example, or a one-time-only corporate stage show that I knew was going to go to post. It’s probably the perfect system for reality TV, and it would certainly come handy for many kinds of documentary shooting.

      I’d also spec it if I was worried about recording in a situation with a lot of uncoordinated RF about or if I thought there was a chance the actors/subjects were going to go outside of wireless range. For a film, it could come down to a calculation like, “How much would keeping the cast and crew here for a retake — or getting the actor for an ADR session — cost the production vs. the extra rental on the gear?” Rental-wise, it’s more than twice the run-of-the-mill systems, and about 20% more than other high-end stuff. If you’ve got any kind of decent budget it would seem to be almost a no-brainer.

      As I mentioned in the essay, the RF diversity capacities seemed pretty impressive, so perhaps that’s a good reason to go Zaxcom even if you’re not going to record on the beltpacks. Then again, the kinds of impressive new diversity strategies Shure showed us at their Axient intro today were also plenty intriguing, so… We work in exciting times, no?

      February 2, 2012 at 7:46 pm

  2. N. Christopher Perry

    Very neat.

    February 15, 2012 at 11:49 pm

  3. Jesse Henderson

    Very cool read Ken… nothing like a little lead to mess with reception. You look good in those scrubs.

    February 16, 2012 at 2:34 pm

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