This article originally appeared in the June, 2017 issue of Pro Sound News. Innovations is a monthly column where different pro audio manufacturers are invited to discuss the thought-process behind creating their products of note.
One of the main barriers for any IEM or wireless monitor system using digital transmission, or even digital audio, is the incurred latency of the A/D and D/A process. Most digital wireless microphones, for instance, exhibit latency somewhere between 2 to 7 ms, with most in the range of 2.5 to 3.0 ms. While this does not seem like much, and can certainly not be heard as an “echo” or an audible delay in the signal, there is the issue of phase cancellation in the ear of any performer using an IEM to hear themselves while on stage. This occurs due to the difference of time of arrival in the “round trip” signal path of the microphone to the ears vs. bone conduction in the performer’s own head, manifesting as a tonal shift in the higher frequency registers. According to many sources, a maximum round trip latency target before most performers start to notice this tonal shift is 2.0 ms. As you can see, this is a difficult challenge.
Lectrosonics has been well aware of this obstacle for many years, beginning with the development of the Quadra digital IEM platform in 2011. Although this product was not ultimately a fit for the marketplace at the time, it set the standard for low latency and pristine audio quality when compared to any other available wireless system. Some of the issues with Quadra were the narrow tuning range and the crowded spectrum between 902 and 928 MHz. The Quadra system also occupied between 2 and 4 MHz per channel, depending on settings. This limited the maximum number of channels in any one location to 8, which turned out to be insufficient in many situations.
The Lectrosonics team learned a great deal from the Quadra experience, and went back to the drawing board in an effort to once again raise the bar for IEM systems with a digital platform that would outperform any other existing IEM system on the market while keeping within some of the standard conventions for products of this type. This was a tall order because the established premier systems from the major wireless manufacturers work well. But the downside of those existing systems is that they use multiplexed analog FM transmission over a signal RF carrier to deliver stereo audio. In practical terms, this is very closely related to how FM radio works. Admittedly, the sound is acceptable and the latency is essentially zero. However, as any audio engineer can attest, this kind of analog transmission platform introduces a number of audio artifacts, including companding distortion, dynamic compression, unstable and somewhat narrow stereo separation, and lack of extended, clear bass response.
The design effort for the Lectrosonics M2 Duet system centered on these main points: First, it had to be an all-digital platform with latency below 2.0 ms. Secondly, the audio fidelity and operating range had to be superior to any system available. Third, the audio input configuration needed to be flexible enough to accommodate both analog line-level signals and digital signals via Dante. And the final goal was that the transmitter would be more compact than other units, in an effort to save rack space and, ultimately, save cost when installing larger systems.
The new Duet system has not only met these goals, it has exceeded them. The analog-to-analog latency for the Duet system is 1.4 ms, or about half that of most digital wireless systems. The audio fidelity with the 24-bit digital stream is something to behold, with crystal clear, extended bass response, wide, stable stereo image and a complete lack of dynamic compression. The operating range, due to the 8PSK coding with forward error correction, coupled with the innovative receiver filtering arrangement, is better than any other system Lectrosonics has tested—even systems with more than twice the RF power at the transmitter. The M2T Duet transmitter accepts either line level analog or digital inputs via Dante network. And, finally, the transmitter is a half-rack unit with two stereo transmitters inside, yielding twice the rack density of any comparable system, while keeping costs reasonable.
Another major design goal for the system was the flexibility of how the receiver can be configured, since it is likely to be used in one of three ways: as a performer IEM system, as an IFB system for broadcast applications and as a monitor system for film sound boom operators. Thus, a detail-rich, high-resolution color display was integrated into the receiver, with a wide range of menu options that allow the user to customize a number of important parameters. The M2R receiver can be set up in stereo or mono, offers a wide range of limiter options, allows for fine tuning of stereo balance and offers a high-frequency boost at 5 or 7 kHz for some performers. In addition, the receiver can scan the available RF environment on site and upload this information to the transmitter and thus to the Lectrosonics Wireless Designer software platform for channel management and frequency coordination.
The Lectrosonics Wireless Designer software platform was originally developed for the DSW (Digital Secure Wireless) platform and was introduced in 2014. Since then, connectivity has been added for Lectrosonics Venue and Venue 2 receivers and now the new Duet system is included as well. This allows users to manage scan data from multiple devices, execute frequency coordination and monitor all systems centrally. Since the Duet system has twoway IR ports on the transmitter and the receiver, data can be exchanged, modified and re-sent. Coordinating frequencies alongside those for the wireless microphone systems is quick and easy. A frequency list from IAS (Intermodulation Analysis System) can be imported and then considered when choosing new frequencies.
After listening to input from our users, Lectrosonics incorporated the FlexList concept, which allows operators to load several profiles into the receiver, then quickly tune between them while on stage. Each profile contains the RF frequency, the name and other important parameters for the receiver. Monitor engineers in particular can then quickly go to any performer’s mix on a stage and hear what they are hearing, helping to troubleshoot any issues on the fly.
As should be evident, the new M2 Duet digital wireless monitor system brings a number of new technologies to the fore, in a well-thought-out package aimed at professional performers, broadcasters and filmmakers. The Dante connectivity, audio performance and operating range alone should draw attention, while the deluxe features are icing on the cake.
Karl Winkler is vice president of Sales & Service for Lectrosonics, Inc., where he provides frequency coordinations and system design assistance to a wide variety of clients. Winkler started in audio by making binaural recordings while in Jr. high school. Following a Certificate of Advanced Studies from USC, he joined the U.S. Air Force and toured as FOH engineer with the Airmen of Note big band during the 1990s.