We told you that we were going to lay off the discussion of wireless audio technology for a while. Well, we lied. It seems like developments in the wireless world are happening so fast that by the time the ink dries around here, there’s more news to report. So this month, we shine the spotlight on X2 Digital Wireless Systems and Audio-Technica. X2 Digital (www.x2digitalwireless.com) — with a bit of help from Audio-Technica — has just augmented its XDR Series of Digital UHF wireless systems with four new products: the XDR952 (omni lavalier microphone with A-T MT830-X); the XDR953 (cardioid headset mic with ATM75-X); the XDR954 (cardioid lavalier mic with A-T MT831-X); and the XDR957 (clip-on in-strument mic with A-T Pro35-X).
“Big deal,” you say while you reach for the remote control. Well, yeah it is kind of a big deal. XDR wireless systems are based on multichannel, 24-bit digital wireless transmission. The system features several stages of operation, starting at the XD4 body pack transmitter, which is capable of handling instrument-, line- or microphone-level signals. A 24-bit analog-to-digital converter resides inside the XDT4, and the system transmits the audio signal, sans companding, to the XDR4 Receiver over a 300-foot operating range, using two separate RF carrier frequencies.[For those of you who don’t recall, companding is the process of compressing a signal before transmission and expanding it after reception in an effort to reduce noise, which it does. It can also create some very strange, audible side effects such as pumping and breathing and high-frequency loss. Lectrosonics is another wireless manufacturer that avoids companding].
Transmission from the XDT4 is in the range of 902 MHz to 928 MHz and employs X2’s proprietary Q-DiversityPLUS (a type of diversity recep-tion technology). Q-DiversityPLUS is a dual-frequency broadcast system that ensures that the data being transmitted — your precious audio — is isolated from unwanted interference. The XD4 transmitter turns audio into a unique digital data stream that is modulated over two separate RF car-rier frequencies for frequency diversity.
The XDR4 receiver, with its four receiver sections multiplexed in pairs, executes the next stage of Q-DiversityPLUS. Each set of two receivers works to receive one frequency. Two of the receiver sections connect directly to internal antenna, while two more receive RF signals from external antenna through BNC jacks on the XDR4’s rear panel. All four receiver sections work together to grab the two RF signals that carry the digital transmission. The receivers are smart enough to recognize only the digital data that originates from the XDT4 transmitter, effectively “locking out” competing sources of RF interference.
An onboard microprocessor analyzes the transmitted data, sorts it out and sends it to a 24-bit digital-to-analog converter, resulting in a dynamic range in the vicinity of 118 dB with a frequency response from 10 Hz to 20 kHz. Since XDR systems operate in the 900 MHz band, they are (at this moment) free from DTV and FCC licensing concerns and may be run on any of five user-chosen operating channels. The result is an increase in the resistance to interference from competing technologies and better performance under “hostile” RF conditions.
So far, so good. So what? Here’s the kicker: All X2 Digital Wireless XDR systems are “2009 compliant,” giving them the ability to operate freely throughout North and South America without frequency coordination issues or concern for DTV and the “white space” issues we have been jump-ing up and down about over the past year. In other words, X2 says “digital television, hostile RF environments? Bring ‘em on.”
In addition to microphones from Audio-Technica, XDR body-pack transmitters can be used with headset, ‘lav or instrument microphones from other manufacturers when wired with a 1/8-inch TRS connector. Furthermore, XDR products are backward compatible with previous products in the company’s XD Series of wireless components.
Audio-Technica (www.audio-technica.com) is working on wireless technology from a completely different angle. (The company has incorporated Ultra Wideband wireless technology from Multispectral Solutions Inc., using it for the first time in commercial sound applications. Believe it or not, UWB dates back to the 1800s and Marconi, when it was used for long-range communications. Dubbed SpectraPulse Ultra Wideband, the sys-tem does not employ conventional wireless channels and carrier frequencies. UWB uses a series of extremely short (nanosecond) pulses that oc-cupy an instantaneous bandwidth of 500 MHz within the 6 GHz frequency spectra. The signals are broadcast in precisely timed sequences, result-ing in reliable, coded transmission of information.
What’s really interesting about UWB is that (in addition to being extremely short) these pulses are broadcast at an extremely low level. Our current wireless systems typically broadcast a signal with strength of about 50 milliwatts of power. SpectraPulse transmission strength is roughly 40 nanowatts, placing it down near the RF noise floor of the typical environment. Ironically, this low signal level makes SpectraPulse transmission difficult to detect by all receivers other than the UWB device(s) that have been programmed to decode the precise sequence of data pulses. Since SpectraPulse operates in a region of the RF band where few other RF devices have been licensed, interference is unlikely. In other words, UWB is kinda’ invisible to other wireless technology.
Current SpectraPulse products from Audio-Technica include the mtu101 Microphone Transmitter Unit (boundary mic), the drm141 Digital Re-ceiver Module, the aci707 Audio Control Interface and the cei007 Charger Encryption Interface. At this time, SpectraPulse is intended for use in conference rooms, courtrooms and corporate events, and supports 14 simultaneous channels. With a sample rate of 24 kHz, audio bandwidth of a UWB system is approximately 100 Hz to 12,000 Hz, latency is around one millisecond and the system does not employ companding. I think we can expect to see this technology extended to instrument and handheld vocal mic applications in the near future.
Score two for the wireless geeks!
Steve “Woody” La Cerra is the tour manager and front-of-house engineer for Blue Öyster Cult. He can be reached via e-mail at Woody@fohonline.com.
