Building the Perfect Audio Bag

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Have you ever wondered what’s going on inside the audio bags that are used in professional video and film productions? In this article we’ll take a close look at the gear found in a typical professional location sound bag, and explain what each piece of equipment does. You’ll gain an understanding of how all these devices connect together and why each tool is necessary to have.

Before we get started, it’s important to note that not all location sound bags contain the same equipment. A professional sound person could have a variety of different configurations of gear inside their bag, depending on the specific needs of the current project they’re working on. With that in mind, here’s a list of the most fundamental equipment found inside a basic field audio bag:

  • A portable field mixer
  • Wireless microphone systems
  • A shotgun microphone and boompole (which are not found inside the bag itself—but essential)
  • Wind protection for the mics
  • A field recorder
  • Headphones

Let’s start out by talking about the bags themselves. Field audio bags are not glorified fanny packs, nor are they simple shoulder bags with a clear flap on the top. Location audio bags are purpose-built to hold field audio equipment. However, they’re not designed for storage. They’ve been made to position and protect the audio equipment while you actively use it.

Location audio bags usually have small openings inside of their pockets and compartments that allow you to feed cables through to all of the different areas of the bag. This way, if your field mixer is in the main compartment, you can connect an output cable to a portable recorder that’s inside the front pocket. It’s important to be able to connect all the cables internally without exposing them to the outside of the bag. This helps to protect the gear from the elements, and makes it less likely to accidentally snag and pull a cable, which could potentially damage the equipment, cables and the person wearing the bag.

Location audio bags can be worn by people of varying sizes, but they’re not “one size fits all” for the equipment. If you’re using a large field mixer with five channels, you’re going to need an audio bag wide enough to accommodate it. When you’re putting a location sound bag together, it’s usually a good idea to determine the exact model of field mixer you’re going to use first, and then pick out a bag that will work well with your mixer. Other factors you should consider are the number of wireless receivers that will be used and the size of your portable audio recorder.

Field Mixers

The field mixer is where you connect all of your microphones (both wired and wireless) and other audio sources. The mixer enables you to create a sound mix to send to the cameras and your audio recorders. It's also where you plug in your headphones so you can hear what's going on, and make the important decisions about how to mix the sound. Field mixers often feature multiple outputs, so you can feed audio to several different devices simultaneously.

What makes a portable field mixer different from other kinds of audio mixers? First of all, it’s portable; meaning that it can run on batteries. It’s not uncommon for a portable field mixer to lack a Master level fader; meaning that you can easily adjust the levels of the separate channels but not the Master output. Many portable field mixers feature a built-in tone generator. This allows you to calibrate the recording level of other equipment with the output level of the field mixer (such as the video cameras, portable recorders, etc.). Calibrating with a tone generator helps you avoid sending other equipment an audio signal that’s too loud, so you don’t end up with clipping and digital distortion.

The main thing you need to be concerned with when choosing a field mixer (besides the overall build and sound quality) is the number of channels it has. Some applications will never require more than three channels, while other jobs (such as doing the sound on a reality TV show) will require more.

Wireless Microphone Systems

Wireless microphone systems are an incredibly important part of a location audio bag. A single wireless microphone system consists of three parts: the microphone, the transmitter and the receiver. You attach a lavalier mic to your subject and you plug it into a beltpack transmitter. You then affix the transmitter to the subject’s belt (or fasten it to another part of their body). The wireless receiver stays inside the audio bag, with its output connecting to an input on the field mixer. Therefore, two thirds of the wireless system is attached to the talent, and just the receiver is inside your bag. You need all of these things to operate a single wireless microphone. If you need to use multiple wireless microphones, you will need a mic, a transmitter and a receiver for each one of them. It’s not uncommon for a professional sound person to have four or more receivers in their bag.

There’s a wide variety of battery-powered wireless microphone kits available, but it’s always a good idea to get the best quality system you can afford. The airwaves are becoming increasingly congested with consumer gadgets. A lesser quality wireless microphone system is more likely to experience static, dropouts and interference. Better-quality systems not only sound better, but they’re more reliable, and when you do experience a lot of traffic in the airwaves they make it easier to find clear frequencies to transmit on.

You can find out more information about professional wireless microphone systems in this B&H inDepth article.

Shotgun Microphones and Boompoles

Some of the most important parts of an audio bag don’t live inside the bag at all. No location sound kit is complete without a good boompole and a few different kinds of mics to use on it. The most common kind of mic that people associate with boompoles is the shotgun microphone. Shotguns are an excellent choice for recording dialog in certain kinds of environments in film and video production.

Other kinds of microphones are frequently used on boompoles as well. One of the most common is the small diaphragm hypercardioid microphone. Hypercardioid microphones are a great choice for booming dialog in indoor spaces. Shotgun microphones tend to pick up too many reflections from the floor and walls when used in smaller indoor spaces. Hypercardioids don’t suffer from this issue and will often capture a more natural sound. In larger rooms and outdoors, shotgun microphones are the preferred microphone for boompole use.  If you want to learn more, check out this B&H InDepth buying guide dedicated to shotgun microphones.

The boompole itself is another interesting piece of equipment. Many newcomers want to know the differences between a boompole and a broom pole. There are many. A good boompole will be easy to collapse and extend, and be able to do so silently. They are lightweight, yet durable enough for a tough life in the field. Some boompoles feature an interior cable, which makes set-up and breakdown times faster. Some will be made out of carbon fiber to be even more lightweight. The lengths, quality of the materials, and the quality of the locking collars all affect the overall cost of the pole.

Wind Protection for Microphones

Proper wind protection is one of the most important accessories in a location audio kit. Most microphones come with a basic, sponge-like foam windscreen. They are useful for indoor booming (to avoid distortion from drafty air), but totally inadequate for outdoor usage.

Microphones have incredibly sensitive capsules that pick up sound from changes in air pressure. When you take a microphone outdoors (even on a nice day), it doesn’t take more than a gentle breeze to compromise the capsule’s ability to pick up clear sound. The wind doesn’t damage the microphone; it just completely mangles the sound that it picks up.

Additional wind protection is always used on microphones outdoors. Shotgun microphones get mounted into blimps (which are also referred to as “dead cats”), and even tiny lavalier microphones get used in special fuzzy windscreens. These contraptions use artificial fur to silently diffuse rushing wind, and they’re very effective.

Field Recorders

Field recorders (which are also referred to as “portable digital recorders”) are used to record the sound that the microphones and other equipment have picked up. It’s a common practice for a professional location sound person to record a copy of the audio in their bag when shooting is taking place. It’s not uncommon for the sound person to also send an audio feed to the video camera.

There are many different sized and shaped field recorders on the market. Affordable pocket-sized portable audio recorders have become very popular with consumers. These devices can be useful for making a back-up copy of the audio in the bag for lighter jobs when only two tracks are being recorded. When you need to record multiple isolated tracks of audio, and when syncing and jamming to time code is necessary, a more professional field recorder will be needed.

On some kinds of shoots it makes more sense for the location sound person to record all of the audio directly into the field recorder, and not use a field mixer at all. This practice has become popular on the sets of larger-scale reality television shows. Because the dialog is unscripted, it doesn’t make sense for the sound person to try to mix the levels on the fly. Instead they will just record all of the microphones onto individual isolated tracks, and let the post-production crew sort out the sound mix.

Headphones

Headphones are one of the most important parts of a location audio kit. They’re as vital to a sound person as the viewfinder is to a camera operator. Professional sound people use closed-back headphones that provide a flat frequency response, so they can hear exactly what the audio sounds like. Because the headphones will often be worn for long stretches, it’s important that they be extremely comfortable. Headphones that fold up and collapse for travel can also be useful, because location audio people often have to break down and pack up their kits several times a day.

So, those are the most basic ingredients found in location sound bags, but there’s a lot more equipment that’s also commonly used. Battery distribution systems are popular among production sound professionals. These allow you to spread the power from a single NP1 battery to every battery-dependent piece of equipment in the bag. Using a battery distribution system offers many advantages. You won’t have to keep track of the battery life in each separate piece of gear, because they’re all sharing the same battery. In the long run, using a system like this will save you money over buying disposable batteries (and it’s better for the environment). Plus, you can power on and off all of the equipment in the bag with one switch.

Breakaway cables are another tool often used with location audio bags. They connect the outputs of the field mixer to the inputs on a video camera. Many breakaway cables have headphone jacks incorporated into the wiring that enable you to listen, remotely, to the audio that's being recorded into the camera. This way you can be sure that the audio being recorded into the camera isn't distorting and that everything is 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.

IFB systems are also commonly used with location audio bags. An IFB system enables you to transmit audio wirelessly to a remote pair of headphones. These systems are used when a director or other crew member needs to listen to the sound mix of the shoot as it takes place.

Hopefully this article has given you a solid, basic understanding about what’s inside a location audio bag. If you have any questions about this equipment, we encourage you to post them in the Comments section below!

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q about when recording live audio....
aren't many mics stereo? how come many preamps are one channel? does this mean the preamps are mono not stereo? are there preamps that maintain the stereo recording from a stereo mic using a single xlr? it seems that when recording into a recorder that a xlr input or channel is recorded as a single channel mono and not as a stereo channel. is this correct?

Most mics are not stereo there are some that are but not many. There are settings in most recorders where you can change the record setting from multiple mono which records two seprate mono files or intreleaved which is a sterio file. Stereo microphones still record to one one channel they just record in a diffent polar pathern unless it really is a stereo mic with two cables. hope this helps

Thank you so much, this has taught me a lot!

I'm unsure about one thing though: what is the difference between a field mixer and a field recorder? Are both essential, or can someone operate fully with just a field mixer?

Thanks again,

Avi