Basic Audio Techniques for Video: Wireless Mic Systems

This installment of our blog series on Basic Audio Techniques for Video explains the basics of working with wireless mic systems.

If you missed the previous installment discussing how to avoid wind noise when recording outdoors with lavalier microphones, you can read it here.

In order to produce a great video, you need great sounding audio to go along with your picture. In some instances, a wired microphone may not make the most practical sense, or you may simply prefer the freedom of movement a wireless mic offers. There are some simple techniques to help get the best performance from your wireless microphone systems.

AT01Wireless Microphone Basics

It’s always important to ensure that you have a copy of the manual that matches your wireless mic system. There is a wide variety of makes and models for wireless mics and not all are created equal. Some instructions can even change from model to model within the same brand. There are some basics that are common among most models, however, specific menu settings and buttons may vary across different manufacturers and models.

Batteries

The most common issues with wireless mics on a shoot are the result of weak batteries, especially in the transmitter. Start every recording session with a fresh pair of batteries in your units. Plan to swap out the batteries for a fresh pair about four hours into your shoot, perhaps around lunchtime, until you get more familiar with a particular unit’s battery life.

Most manufacturers advise against the use of common rechargeable NiCad or Nickel Metal Hydride cells. These types of batteries tend to drop to a low voltage level fairly quickly, even though they are able to hold a lower voltage for a long duration. Fresh alkaline batteries start off with a higher voltage that diminishes much more gradually. Not having to worry about recording audio with a low battery makes for a less stressful recording experience.

Some models, such as the System 10 camera-mount wireless system, utilize a built-in lithium ion rechargeable battery in the receiver that can operate for up to 12 hours. In order to make them last the duration of your shoot, ensure they’re fully charged the night before. While it’s possible to power them from a portable USB battery pack in a pinch, it’s easier not to worry about charging them while recording.

Frequencies

AT02After completing your battery check set all your wireless mics to the best operating frequencies. All pairs of traditional UHF receivers and transmitters need to be set on matching frequencies.

To start, select a frequency for your first system and leave them turned on. Then, scan your next receiver to choose another frequency and set the matching transmitter. Continue this process for all the systems to be used in the shoot. Remember, there’s a wide variety of frequencies to choose from, so you can allow some space in between them. Keep your systems organized by labeling receivers and transmitters that are in the same set.

There may be other radio devices on or close to your chosen frequency. One way to detect interference is to turn off the matching transmitter and watch the indicator light for each receiver antenna. When the transmitter is turned off, neither light should come on at all. If either antenna light shows any activity, it’s picking up an unwanted signal. It can also help to listen to the receiver for any electronic chatter.

All manufacturers include additional frequency information in the manual or online for easy reference. Some of the newer systems on the market operate in the 2.4 GHz range and are frequency adaptive. They automatically change frequencies to avoid interference. Simply pair those systems to each other.

Mics

Your choice of which lavalier to use will greatly affect the overall sound quality of the audio, regardless of whether you’re using a wireless or hardwired system.

To set the microphone input level on the wireless transmitter:

• Plug your headphones into the receiver. Start with the knob turned to the lowest possible position.
• While speaking into the mic, raise the level gradually until it begins to sound clear and bright.

Remember, you don’t want to see the peak indicator come on steady, but occasional flashes are ok with loud transients.

You can get the best performance out of your wireless system by thinking of them as “wireless cables.” There are mic connectors at either end that are linked to each other by radio waves. Pay attention to this invisible pathway. Radio waves can be deflected or even absorbed by human bodies, metal stands, electronic equipment, power cables, or metal furnishings and props.

To improve the wireless path, it’s generally easier to remote an entire portable receiver. Although some receivers have BNC mounts that readily allow you to use RF cables to remotely mount your antennas. There are systems that can easily improve the wireless path by allowing the use of an Ethernet cable to remote the receiver modules, like Audio-Technica’s System 10 Pro.

Additionally, a good strategy is to shorten the path and avoid RF obstacles by setting up the portable receivers closer to the talent, on the edge of the set or hidden within the set, then run balanced audio cables back to the recorder.

Accessories

An XLR-to-transmitter audio input cable, such as the Audio-Technica XLRW, is a helpful accessory to add to your sound kit. The XLRW offers a female input for microphones or boom poles. If the mic requires phantom power, some sort of inline battery power supply will be needed. The XLRW will work with battery-powered condenser mics like an AT897. Additionally, the XLRW can be utilized to transmit an audio feed from a mixing board to a camcorder.

Along with the XLRW cable, belt and pouch kits are also a good accessory to include. They’re used to secure body-pack transmitters to talent. The pouch holds the transmitter and, with safety pins, can be fixed to the inside of clothes that lack pockets or provisions for a metal belt clip.

While using a waist or garter belt, the pack should be secured on the inside of the belt, up against the body. It shouldn’t be left to hang freely. When moisture becomes an issue, such as in instances of rain, water spray, or excess body perspiration, many professionals will protect the body-pack transmitters in dry, non-lubricated condoms.

Lastly, when rigging a body-pack transmitter on the talent, take care not to cross the microphone line with the antenna, as pictured below.

AT03

To keep this from happening, you can simply flip the body-pack around so that the two never cross, as pictured below.

AT04

It’s acceptable to bunch the excess line from the mic together, but make certain the antenna remains as straight as possible. Soft or easily flexible antennas can be kept straight by slipping a rubber band over the tip and using a safety pin to keep the antenna in position. The rubber band will stretch with the actor’s movements or will break if they put too much strain on the pinned antenna.

These basic tips will make utilizing wireless audio for your video shoot simpler and more straightforward. Whether you’re in the studio or on location, Audio-Technica always has you covered.