Close To The Source

The progress of digitizing sound reinforcement audio signals is moving from the loudspeaker processor back up the signal chain to the mixer and finally the microphone. While it may be a few more years before we have a wide selection of microphones that output a digital signal, there are already a number of mic pre-amps that do. Converting the signal as soon as possible can capture the very best signal from the mic output. To do this, a number of aspects of the mic pre-amp, A/D conversion and remote control features must be considered.

There are a number of compelling reasons to have the mic preamps onstage, rather than at the much more distant FOH mixing console. The delicate signal from a microphone can suffer the audible effects of high-frequency loss, induced noise and drop outs just trying to get from through the mic snake. Dynamic microphones depend on the quality of the output transformer to make this journey successfully. Condensor microphones can actively drive the line but the phantom power can sometimes generate ugly sounds when the mic snake is walked on or has road boxes roll over it. In many portable systems it is difficult to get two different paths to the FOH, so AC power cables are run parallel or even bundled with the mic snake. It is little wonder that live sound systems are notorious for poor signal-to-noise relative to their installed counterparts.

Placing the mic preamp on the side stage is obviously a great improvement to the signal quality, unless you lose control of the gain structure and warning indications. After all, it doesn't matter how quiet, clean and clear the mic signal is if it goes into clipping distortion on the first chorus. To maintain confidence that the gain of the preamp is correct and can be changed to suit those sudden changes during an event (not that a sax player would ever walk up to an acoustic guitar mic to play a solo) it is necessary to have both control and status indication for the mic preamp at the FOH mixer. This leads to a data path and display technology at each mixer to show gain settings, input levels and allow remote adjustments to be made.

Sharing a high quality mic preamp between both monitors and FOH mixing consoles can clean up the signal but may lead to gain management issues. Ideally, a separate gain (sometimes just on the split output) allows the monitor engineer to optimize his or her gain structure independently of the FOH settings. It has always been scary for the mic gains to be adjusted from one console but feed both, as it always seems that the gain adjustments happen when there is little time to warn the other person. To complicate matters further, there may be a remote recording or broadcast mixer that also needs to share these microphone feeds, with entirely different concerns about the gain settings.

There are a wide variety of potential solutions to these problems, from conventional mic preamps with remote controls, including sophisticated mic splitters, to mic preamps that form the front end of fiber optic interfaces. The fiber optic approach has been out with a number of touring productions over the past few years and can offer the most versatile splitting and patching functions imaginable. Once the signals are in the optical format, providing a drop box with just the mic signals you need, in the order you want, is very straightforward. In addition, even an extremely large number of input channels can be carried in a surprisingly robust, yet tiny, cable to the FOH mix position.

The latest form of FOH mixers doesn't even require the microphone signals to travel out into the house. Instead, the mixer is simply a control surface for audio processing that remains onstage. There are both the analogue approach, such as the Soundcraft Broadway (already on the road for a few years), and the digital approach, such as the Yamaha PM1D (should be on the road this fall). These mixers form smaller and less weighty controls for a rack of onstage processing that was, traditionally, contained inside the mixer. Both of these examples retain familiar control surfaces but add the power of instant reconfiguration that has been a familiar feature of studio consoles for many years. The only audio that must be sent from the stage to the mixer is the monitoring/solo bus for the headphone feed. Using multiple control-only consoles that all communicate to a single processing rack (which includes the mic preamps) can alleviate many of the gain management issues noted above. It all seems so obvious that the next generation of live sound techs will wonder why we ever carried the mic preamps way out into the audience. What were we thinking!

United Entertainment Media Inc.
460 Park Avenue South, 9th Floor
New York, NY, 10016
Ph. 212-378-0400
FAX 212-378-2160

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