Note: This review originally appeared in Sound & Video Contractor, March 2010, and in SVConline.com. It is reprinted with permission from Penton Media. Click here to download a PDF of the review.
Mar 19, 2010 12:00 PM, By John McJunkin
A high-tech wireless microphone system for the boardroom.
The radio frequency spectrum is getting very crowded, and the scarcity of bandwidth is being compounded by legislation that is chopping up the available spectrum between more and more government agencies and other commercial bands. It continues to get harder and harder to find a clear frequency, and the more frequencies are required for a job, the more complex and difficult it gets. Contractors are in need of solutions that overcome these difficulties, and Audio-Technica has obliged with its SpectraPulse system. This is the only true ultrawideband (UWB) system in existence, and it brings some pretty high science to bear to solve the problems that contractors face. I spent time with a SpectraPulse system, and I was wowed by that high science but also impressed from a pragmatic standpoint. The system is simple to use and works exactly as advertised.
I'm not going to pretend to understand in great depth the technical workings of the SpectraPulse system, but allow me to offer a simplified explanation: The system is based upon time division multiple access (TDMA) channel access, the same technology used for most 2G and some 3G cell phones. The TDMA architecture allows 15 time slots of information per millisecond, and during the first of these time slots, the Audio-Technica drm141 digital receiver module transmits to synchronize and send status and control. Each of the system's 14 transmitter channels then has an opportunity of one time slot in duration to transmit its data to the receiver. Each transmitter sends its data sequentially during its respective time slot, and during the other 13 time slots, it queues its data for transmission during its next slot. This limits latency to less than 1.5 milliseconds. This system facilitates fast bidirectional communication between transmitter and receiver, which in turn helps to avoid sync loss, and much faster reacquisition if sync is lost, typically 3 milliseconds or less. Basically, this is digital over the air, which provides ipso facto encryption and allows for the transmission of a multitude of signals with much less bandwidth. Since the system does not use a single carrier frequency per se, it's virtually impossible to isolate and intercept the signal unless the signal thief has a UWB system of their own, and in that case, 128-bit encryption is available.
The system's transmitters are the mtu101 microphone transmitter unit and the mtu201 XLR desk stand transmitter. The mtu101 incorporates a boundary microphone and is roughly trapezoidal in shape. It is about 3" x 5" x 2". On its underside are a sliding power switch and a recessed rotary switch to determine on which of the system's 14 channels the unit will transmit. I used a standard tweaker tool to make the necessary adjustments. Atop the unit are LEDs to indicate power and link status. Additionally, the power LED will blink if the unit's batteries are failing. I like this a lot. It can use NiMH batteries or standard AA alkaline batteries, and Audio-Technica includes a pair for each transmitter—a nice touch if a contractor needs to get the system up and running immediately. A soft-touch button on each transmitter can be configured as push-to-talk, push-to-mute, or in toggle mode. This microphone/transmitter cuts a low profile and is therefore nice for installs that require clear lines of sight. The mtu201 is virtually identical to the mtu101 in topology and operation, but it's just a bit "taller" as it were. It offers an XLR input intended for use with an included gooseneck microphone, but any signal can be connected to the mtu201's XLR input. It struck me that these could be useful in a multisignal cart scenario, for example, a drum kit on a wheeled platform.
The drm141 integrates the system's UWB antenna and logic required to send the signal along a Cat-5 cable of up to 300ft. in length. It recesses into a wall or ceiling in the space of a 3-gang electrical box and is otherwise simple, with just its RJ-45 jack facilitating connection to the aci707 audio control interface. The aci707 demultiplexes the audio, making it available via Phoenix connectors on its rear panel. Up to seven channels of audio can be routed from each aci707, so two units are necessary to take advantage of all 14 channels made available by the system. The aci707 also features dipswitches that determine toggle mode, local control, channel assignment, active mode, and mic level output. Its front panel has per-channel LED indicators for link mode, muting, switch closure, and low battery. An RS-232 connector enables its connection to Audio-Technica's charger, the cei007, which also facilitates the programming of 128-bit encryption for up to seven transmitters simultaneously.
I unboxed the system and placed the drm141 up high and in line-of-sight with the system's transmitters, per the manual. The receiver exhibits a directional reception pattern and must be in the same room with the transmitters. I connected it to the aci707 and powered the aci707 on. As I powered on each transmitter, the green link LEDs on the front panel lit up, and very quickly at that; the system did not have to hunt for available frequencies. I monitored the output of the aci707 via loudspeakers in the same room. The mtu101 boundary mic units worked nicely, providing more than sufficient gain when I placed them on a table top. The mtu201 gooseneck units also provided an excellent signal. I experimented with moving transmitters out of line-of-site, and indeed, I discovered that the reception pattern of the drm141 is quite directional. I also experimented with connecting quite a number of musical instruments to the mtu201 transmitters via DI box, and I was pleased with the results. I chose to do this because I had been skeptical about the system's audio quality given its limited bandwidth, 100Hz to 12kHz. Of course the "air" frequencies above 12kHz were not conveyed, yet the quality was still better than just passable. Still, I'll be looking forward to future revisions that open up the bandwidth closer to 20Hz to 20kHz. There were absolutely no glitches, static bursts, or any other audible interference whatsoever. The noise floor was virtually inaudible, and the D/A conversion quality was very good.
This system is right out on the bleeding edge of wireless technology, and as a result, it is not inexpensive. If the budget allows, the system is worth the money because it's simple to use while at the same time providing a good quality (if bandwidth-limited) signal that is as close to being 100 percent interference free as possible. The inherent signal security combined with the optional 128-bit encryption will satisfy even the most strident requirements. I strongly recommend this system for high-end installs.
John McJunkin is the principal of Avalon Podcasting in Chandler, Ariz. He has consulted in the development of studios and installations and provides high-quality podcast production services.