Anatomy of an Audio Bag

By Sam Mallery

In the past, the B&H newsletter has explained some of the different elements found inside of field audio bags. We've published articles about portable field mixers, wireless microphone systems, field recorders, and battery distribution systems, but we've never put it all together and described how these separate devices act as one. This guide has been created to familiarize you with the equipment and accessories found inside of audio kits used in video and film production. I'll explain what each piece of equipment is, what it connects to, and why it's necessary. The goal is to introduce this stuff to people who may not be familiar with the inner-workings of field sound, and perhaps introduce some new technical strategies to experienced sound professionals. Either way, this article will hopefully be a little less messy than dissecting a formaldehyde soaked amphibian.

Watch this informative video on the Anatomy of an Audio Bag

Putting together an audio kit can be a wise investment for active production enthusiasts. It will help you achieve a higher degree of sound quality in your own projects, and you may even be able to rent it out to acquaintances for outside jobs. This equipment can potentially pay for itself, while also raising the bar for your own production capabilities-- a win-win situation all around. The main hurdles are obtaining the gear, and getting comfortable using it. And now, the first incision…

An ENG audio bag

The most basic ingredients found in an audio bag are a field mixer, a few wireless microphone sets, headphones, a boom pole and some boom mics (which aren't contained inside the audio bag, but are absolutely essential to the kit). ENG stands for Electronic News Gathering. You can use an ENG kit for journalistic purposes, but it can just as well be used for shooting film or television. In regards to audio bags, the term ENG generally means that the kit is slimmed down to be lightweight and easily portable. ENG kits are used when the job at hand isn't extremely complex. If you only need a couple of wireless microphones and a boom for a shoot, an ENG bag is the way to go. If you're going to need several wireless mics, a boom, timecode sync, a portable recorder, IFB feeds (more on this later), then you may need a more substantial audio kit.

A few of the elements of a basic ENG bag are the bag itself, a field mixer, a wireless kit, and a good pair of headphones

Essential equipment for an ENG audio bag

Field Mixer – A portable mixer is the heart of an audio kit. It's where you plug in all of the microphones and audio sources, and send the mixed audio to the cameras and field recorders. It's also where the audio operator plugs in their headphones to hear what's going on and conduct their work.

Audio Bag – I list the bag second because what bag you need depends entirely on what kind of mixer you have. The bags are custom designed to accommodate specific models of mixers. These bags usually have compartments for wireless receivers and other equipment, padded shoulder straps and options for harnesses. There are many cleverly placed slots that allow you to feed wires through the separate compartments to have all of the equipment working together, while still being protected from the elements and strapped to the audio operator's body. There are many options available in this category from Petrol, Kata, Porta Brace, and Sound Devices.

Wireless Microphones - A single wireless microphone system consists of three parts: the microphone, the transmitter, and the receiver. The microphone attaches to the transmitter and is used remotely. The receiver stays inside the audio bag, with its output connecting to an input on the field mixer.

Boompole & Boom Microphones – Boompoles come in various sizes (for more information check out this B&H Educational article about boompoles), and depending on what kind of environment you're working in, a shotgun microphone or a small diaphragm condenser microphone will be used on the pole (for more information check out this B&H Educational article about alternative microphones for boompoles). Having the proper wind protection for the boom mic is also very important (check out this B&H Educational article about wind protection).

Breakaway Cable – A breakaway cable connects the two outputs of your mixer to the inputs on a video camera, or other recording device. They are also referred to as "snakes" because they are several cables bundled into one. Many breakaway cables have headphone jacks incorporated into the snake that allow you to remotely listen to the audio that's being recorded into the camera. This way you can be assured that the audio isn't distorting, and that the cables connecting you to the camera are working properly. There is a small mechanism approximately 1.5 feet from the video camera's end of the breakaway cable that allows you to detach it without having to unplug all of the jacks, hence the term "breakaway." This allows the camera operator to freely move the camera to set-up another shot without having to be tethered to the audio person.

An EFP audio bag

If the task at hand requires a more complex portable audio set-up, such as a reality television shoot that requires numerous wireless mics, then you need to assemble an EFP bag. EFP stands for Electronic Field Production. The basic components of an EFP bag are identical to an ENG bag, there is just a little more of everything. Instead of a 3 channel field mixer you would use a 4 or 5 channel mixer, or use multiple mixers slaved together. You may be using two breakaway cables to send the mix to multiple cameras, as well as recording everything onto a multi-channel portable recorder. You may even need IFB systems, which enable you to wirelessly transmit your mix to a remote pair of headphones. These systems are used when a director or crew member needs to listen to the audio of the shoot as it takes place.

More complex jobs require more complex audio kits

Additional equipment found in an EFP audio bag

Larger Field Mixers – In EFP bags you will typically find portable field mixers with more than 3 channels, which allow you to run more wireless microphones, among other things. Larger mixers tend to have more outputs as well, so it's possible to send your mix to several separate cameras through breakaway snakes and wireless systems.

Time Code Equipment – In shoots where you're working with professional video cameras, it can be extremely helpful for post production to lock the audio to time code (learn about the basics of time code in this B&H educational article). Generally there is one device that will provide the master time code, and the other equipment in the shoot will sync to this master generator. Some portable field recorders will have a time code generator, while others may not have a generator but will have an input that allows them to sync with an external generator. Timecode can even be transmitted wirelessly so the audio and camera people do not have to be tethered to one another.

In ultra complex working situations (like a professional film shoot) you may need even more channels of audio, more IFB feeds, an antenna amplification system, etc. For these types of jobs experienced audio professionals will assemble an audio cart. Carts often contain larger formats of portable mixers, and are really another subject all together. At a certain point we would find ourselves dissecting a giant Chinese Salamander, as opposed to a little, lily pad leaping frog.

Thanks for reading this B&H educational article! If you have more questions about field production, don't hesitate to contact us by telephone at 1-800-416-5090, via online chat, or in person at our SuperStore in New York City.

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