As the RF environment grows increasingly hostile, pro audio manufacturers continue seeking solutions for reliable operation of wireless instrument and microphone systems. There’s been a move toward the 2.4GHz band, a part of the RF spectrum that (at least for the moment) can be used by the audio community license-free, worldwide. AKG’s DMSTetrad is a 4-channel digital wireless system operating in that band. Designed for live sound, clubs, corporate, and house-of-worship applications, DMSTetrad provides 24-bit/48 kHz uncompressed audio transmission, 128-bit AES data encryption for secure transmission, and several proprietary technologies to fight interference.
The handheld DMSTetrad Vocal Set is available with AKG’s D5 or P5 capsule. The DMSTetrad Performer Set includes the DPTTetrad bodypack transmitter, C111 LP over-ear microphone and MKG L instrument cable. All versions include detachable antennas, rack ears with front antenna mounts, and antenna front mount cables. Any Tetrad transmitter may be added to the system later, facilitating expansion. For this review Mix received the whole kit-n-kaboodle.
To combat interference from Wi-Fi routers and Bluetooth devices that also live in the 2.4GHz band, DMSTetrad uses several technologies. Dynamic Frequency Selection automatically moves the system to a different channel when interference is detected (aka “frequency hopping”). Time Diversity detects a lost signal and asks the transmitter to resend it. And Antenna Diversity switches to the antenna with the higher signal strength at any moment. The system also employs AKG’s DROCON (DROpout CONcealment), which extrapolates missing information in the case of a dropout, and conceals noises that might otherwise occur.
Controls on the front of the DSRTetrad receiver are minimal but complete. Each channel has LEDs for Battery Status, Link and Clipping, a volume knob, and a single pushbutton for Connect. The rear panel features dual antenna inputs, a power supply jack (12 volts DC 500 mA, included), four discrete Channel Outputs, and a fifth XLR output providing a mix of the four channels. A switch toggles this output between 0 and +20, enabling it to be connected to either a mic or line level input. The remaining switch is labeled Interference Protection. According to the manual, this switch should be set to Low for optimum transmission time unless RFI is a problem, in which case it can be switched to Mid or High. Unfortunately, the manual does not provide detailed information on this feature, but I suspect there might be a small increase in latency when the switch is set to Mid or High.
The handheld DHT transmitter features a power switch and status LED. Unscrewing the battery cover/handle reveals a Connect button and a two-position gain switch (high/low); I would prefer a variable pot for gain but the two settings were adequate. Similarly, the DPT body pack transmitter has a power switch (with safety cover) and status LED. Opening its battery compartment reveals a gain pot, enabling it to be used with either the MKG L instrument cable or C111 LP over-the-ear microphone. All transmitters are powered with two AA batteries.
When setting up the DMSTetrad, frequency selection and pairing is automatic. A brief trip to the Quick Start Guide revealed the transmitter/receiver pairing procedure (see the “Try This” sidebar). The process usually takes a few seconds but on one or two occasions took as long as 10 seconds. There is no manual channel selection, nor visual indication of what channel a transmitter is using.
It appears that AKG intends the DMSTetrad to be used in one of two manners: patch the Mix Output into a single powered speaker (or mixer input), or patch each Channel Output to the inputs of a mixer. Most pros will choose the latter, however the option to use the Mix Output is very attractive for applications where an engineer is not present, or in situations requiring fast, simple setup.
I took the DMSTetrad on the road for a few weeks, using it in various regions across the country. Most often I used the handheld transmitters, but I also briefly used the DPTTetrad body pack transmitter, both with the C111 LP over-ear microphone and the MKG L instrument cable. Typically, I connected the Channel Outputs from the receiver to the inputs of a mixer, though on at least one gig I connected the Mix Out directly into a powered speaker to run acoustic guitar (with pickup) via the DPT body pack and a DHT vocal mic.
AKG’s documentation regarding the outputs leaves something to be desired. Regarding the Channel Outputs, the manual states, “You can connect the microphone inputs on a mixer to these outputs, for example.” I’d feel better if it were stated more like: these outputs operate at microphone level and should be connected to the mic inputs on your mixing console. Also there is no clear indication in the specs regarding operating level of the Mix Output—which, by the way, operates at line level when set to +20 and mic level when set to 0.
Channel Output level is determined by the front panel Volume control. I usually set the DHT to High gain, cranked the Volume until the receiver’s Clip LED blinked red, then backed it off a bit. This yielded a good gain structure that efficiently drove a microphone input. Whether it was due to this or the Tetrad’s overall RF performance, transmission was startlingly quiet, in a “is this thing on?” manner—particularly when using the DHT/D5 combination. RF performance of all configurations was excellent. The only time I experienced RFI was when a Wi-Fi router was literally placed next to the receiver; moving it a few feet away cured the problem.
When I used the DHT handheld with the P5 capsule for a female vocalist, she sounded a bit muffled initially; boosting a few dB at 3.2 kHz brought some presence and air to her voice. Both (supercardioid) capsules were great at rejecting feedback, and their sonic differences were subtle: The D5 has a slightly smoother off-axis response and perhaps a bit more mojo in the lower-midrange. I found the P5 slightly more aggressive in the upper mids, which was perfect for a male lead vocal in a bar band. My biggest surprise was the C111 over-ear mic. I hate headworn mics and with good reason—most of them sound like crap (I am being polite). The C111 just plain sounds good, providing clear articulation while still producing a balanced low end and a surprising amount of ambient rejection. This one’s a no-brainer for presentations or corporate work and easily holds its own for music applications.
AKG built some clever features into the Tetrad system. The BAT light on the receiver turns red when battery performance starts to deteriorate, and blinks red when battery life is down to about an hour. At that point the status LED on the transmitter changes from green to red. The transmitter’s status LED blinks (green) when interference is encountered, which can be helpful in locating dead spots or warning a performer that they are moving to an area of poor RF performance. The set includes rack ears with built-in antenna mounts, and cables to connect these to the rear panel antenna inputs, enabling the stock system to be rack-mounted while simultaneously moving the antenna out of the rear of a rack.
I see the DMSTetrad being comfortable in installed situations, for small tours that don’t require dozens of wireless channels, HOW applications and for rental houses that need to cover a variety of wireless needs. A first look at the price tag might cause a bit of sticker shock, but you have to remember that the receiver includes four independent channels in a single rackspace. Adding a channel requires purchase of only a transmitter, and with an average street price around $200, is very affordable. Of course none of this would matter unless the DMSTetrad’s audio and RF performance was up to the task—which it is. The combination of smart design, high-quality audio, excellent RF performance and expandability should put the DMSTetrad on your wireless watch list.
Steve La Cerra is a New York-based live sound and studio engineer.
AKG’s DMSTetrad features automatic pairing that sets the transmitter and receiver to the same channel. First, power up the transmitter and receiver. Find the Connect button for the receiver channel you wish to use. Press and hold it until it flashes. The system scans the RF environment for an open frequency. Press and hold Connect on the transmitter until both status LEDs glow steady green. They are now paired. To check pairing, push the channel Connect button on the receiver. Its LED blinks and the LED on the paired transmitter blinks. When adding transmitters, DMSTetrad is smart enough to look for a vacant channel that won’t interfere with existing pairs.
PRODUCT: DMSTetrad Four Channel Digital Wireless System
PRICES: DMSTetrad Vocal Set with D5 capsule: $699; DHTTetrad Handheld Transmitter with P5 capsule: $199; DPTTetrad Bodypack Transmitter: $249; C111 LP Over-Ear Microphone: $99; MKG L Instrument Cable: $35
PROS: Easy setup. Excellent RF performance. Four receivers in single-rackspace unit.
CONS: System is limited to a maximum of four channels. Microphone gain is not continuously variable. No visual indication of channel setting.