Audio for Video:
What You Need to Know

Like most churches, yours has probably graduated from video projects that could be taped and recorded by one volunteer with a video camera to more sophisticated digitally-produced programs shepherded by a video crew. Whether you’re the videographer or you’re working with a team, recording a service or a discussion within a ministry, the professionalism of the finished product will depend as much on the audio as the visual quality.

In this issue, we will help you and your team get the best sound possible for your video projects by covering audio-for-video basics – from expanding your knowledge of audio tools, to offering helpful tips and troubleshooting advice.

We’ll cover:

• Links in Audio Chain and What They Do
• Typical Video Miking Applications and Suggestions
• Troubleshooting Tips

The Audio Chain
In the beginning, the first recordings you probably made were with a simple cassette tape recorder. You pressed the Record button, spoke into the microphone and pressed the Stop button when you were finished.



In the world of audio-for-video, you’re going to encounter a few extra links in the audio chain. These will most likely include:

A microphone - that transforms sound into an electrical signal
A mixer - that adjusts the strength of the signal in relation to other signals coming through the same system
Camcorder - When the signal comes out of the mixer (or the optional signal processing device), it is ready to be fed into the audio input jack of a video tape recorder or to an amplifier for playback through loudspeakers.

Microphones
If you’ve read past issues of Shure Notes, you’re probably well versed in microphone characteristics and won’t require a short refresher course. However, there are nuances in video production that make the general subject worth reviewing. Here’s an at-a-glance cheat sheet of the four criteria: physical design, directionality, transducer type and electrical impedance.

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Physical Design

Directionality
Often misunderstood, directionality or polar patterns are actually one of the simplest lessons to learn in understanding how a microphone performs. It’s just this: directionality describes how a microphone responds to sounds arriving from different directions or angles.

Most microphones are available in both types. Lavalier mics are generally omnidirectional; shotgun mics are by definition extremely directional.

Transducer Type
The transducer is the part of the microphone that actually converts sound waves into electrical energy. Also called a cartridge, there are two common types: dynamic and condenser. Since each has specific characteristics that make it more or less desirable for a specific application, it’s important to understand a little bit about each one.

Impedance Ω
This is an electrical characteristic that is something like voltage or current. It is expressed in ohms, the symbol for which is Ω. The choices are low-impedance (low-Z) or high-impedance (high-Z). And this one’s easy: for professional applications, only low-impedance mics should be used. This is due to the fact that high-Z mics begin to sound muffled due to a loss of high frequencies when used with a cable longer than 20 feet. With low-Z mics, you can use cables up to 1000 feet with negligible loss of sound quality.

Important to know:

1. You can determine the type by looking at the microphone itself or its spec sheet. The impedance should be listed right there. If it has a rating of 10,000 ohms or higher, it’s high-Z. 600 or lower makes it low-Z.



2. Don’t match the impedance of your mic to its input. This actually causes a loss of signal level. Low-Z devices like mics should be connected to an input whose impedance is 5 to 10 times higher. This is why mixer inputs generally have an impedance of 1,000 ohms or higher.

Cables and Connectors
These are the least sexy links in the audio chain. Unfortunately, failure to pay attention to this critical gear is often the most common cause of audio problems.

There are two types of connections used between audio devices: balanced and unbalanced. Almost all low-impedance equipment – like microphones – use balanced connections, but there are exceptions. The chart below provides some of the basics that you need to know.

Helpful tips:

1. The type of connector is often a good clue in determining whether a cord or cable is intended for use with balanced or unbalanced devices.
2. Mini-plugs are generally unbalanced and commonly found in consumer audio gear. You can still use a good quality microphone with these connectors by purchasing a cable or impedance transformer with the appropriate connectors.
3. If your gear uses 1/4-inch, mini-plug or RCA connectors, invest in pro quality cables with metal connectors (instead of molded plastic ones) that can be disassembled. These are more reliable, you can make your own repairs if they do develop a problem.
4. Carry spare cables. Cables are the most common point of failure in the audio chain.

Connections commonly used. Left to right:
XLR male,
XLR female,
1/4 inch phone plug,
RCA or phono plug,
3.5 mm mini-plug







Question:
What happens if a microphone with a balanced output must be connected to an unbalanced mic input on a mixer or camcorder?

Answer:
If the cable length is short (less than 20 feet), you could use a mic cable that has an XLR connector on the microphone end and a 1/4-inch or 3.5mm plug on the mixer/camcorder end, or use a standard mic cable and a short XLR-to-1/4-inch or XLR-to-3.5mm adapter cable. This results in the entire length of the connection being unbalanced, which is more likely to pick up electrical noise such as hum or buzz.

If the cable length is more than 20 feet, or greater resistance from noise is desired, a transformer adapter with balanced XLR input connector and unbalanced ¼-inch or 3.5mm output connector should be used. This results in only a very short length of unbalanced connection (nearest the input to the mixer or camcorder).

Mixers
Unless your video recorder has multiple mic inputs or your project requires just one microphone, you are going to need a mixer. A mixer lets you take signals of different levels from several sources and combine them into one signal that can be fed into an amplifier, digital video recorder or other audio equipment.

Automatic mixers (like the Shure SCM810 with IntelliMix®) have special circuitry that senses when a sound is arriving at a microphone and then activates it. These units are able to turn on or "gate" the mic in just a few thousandths of a second so that not even a syllable is missed.

Tip: Monitor your audio. It’s not at all uncommon for sound or noise levels to change significantly during a shoot. If you’re not actively listening, you may not know about distortion, background noise, or other problems until it’s too late. Use a pair of lightweight headphones or earphones and listen at the recorder (best) or mixer (good).

Camcorders
Here’s where the technical end becomes a little tricky. Camcorders use a variety of microphone inputs, connectors and wiring schemes and at this point, there are few standards to which manufacturers adhere. Since many basic video recorders have built-in microphones, determining if and how external mics enter the picture can be a little frustrating.

I have an external mic jack. Now what?
Then, you need to think about making the right connections. Here are some questions that will send you in the right direction:

1. Is the camcorder mono or stereo? If it’s stereo, you’ll want to record the audio from your mic onto both the right and left channels. Assuming that you have a mono signal coming from your microphone or mixer output (that’s the norm), you may need to add an adapter to put the mono signal onto both the left and right audio channels of the camcorder.



2. If it’s mono, does the mic input jack supply DC voltage (sometimes called "Mic Power" or "+3 vdc") for the manufacturer’s own accessory mic? This DC voltage is not the same as the phantom power required by condenser microphones. If you’re connecting your own condenser mic directly to the camcorder, you will still requires a separate phantom power supply. If you are connecting a dynamic mic that does not require phantom power, you still need to avoid the camcorder’s Mic Power, so proper cable wiring is important. The best solution is to use a special transformer that is designed for use with camcorders, like Shure’s A96F Camcorder Interface.



3. If your camcorder is stereo, are there separate mono input jacks for the left and right channels or a single stereo input jack that feeds both channels? If there are separate jacks, do they supply DC power?



4. What length of cable will I need between the microphone and the camcorder? If it’s more than 20 feet, you’ll need a transformer, which not only maintains a balanced connection (minimizing hum and electromagnetic interference) but also boosts the signal level slightly. Typically, you can expect a 6 to 12 dB increase.



5. If your camcorder has an Automatic Gain Control (AGC), you may get better sound by disabling it (usually controlled in a feature menu). Some AGC’s pump up the volume during quiet passages, which may only serve to amplify the background noise.

I can’t add an external mic.
The bad news is that if you want good sound, the built-in mics on most basic camcorders won’t provide it. Here’s why: Most built-in camcorder mics are located on the camera body. Whether omnidirectional or unidirectional, the internal mic will pick up off-camera sounds that are nearby, so the camera operator must be very quiet. The internal mic may also pick up the noise that the camera produces (tape drive, zoom lens, etc.) as well as handling noise. You won’t be able to limit undesired sounds. Check to see if your camcorder has an external mic jack. (The icon for it looks like an old-fashioned stand microphone.) If it doesn’t, you probably won’t be able to connect an external microphone. And if that’s the case, you can still improve the quality of the audio by following these tips:

1. Get as close as you can to your subject. This makes the talker’s voice louder when it arrives at the microphone. The camcorder will automatically turn the mic down, which will reduce pickup of room noise as well as noise from the camcorder itself.



2. Pick a quiet location. Since the microphone is stuck on the camcorder at some distance from the participants, room noise (from air handling systems or adjacent rooms) will be even more audible.



3. Avoid working outdoors. Internal microphones are typically very sensitive to even a slight breeze, which will cause excessive rumbling. Some camcorders have an "electronic windscreen" feature, but try it out in advance to see how it sounds.



4. Isolate the camcorder. Put it on a sturdy tripod, and avoid having the operator touch it excessively.



5. If you’re recording an event or a program, keep the camera running to capture all the audio, even during pauses or short breaks. You can use editing software to eliminate the unwanted video later.



6. Make sure you capture a minute or so of ambient sound to fill in (spoken or musical) gaps in your final edit later on. This can also be used to cover up other sounds (like a ringing phone) that need to be edited out.

Common Video Miking Solutions
Now that we’ve covered the basics, let’s get on to the practical applications. We’re going to assume that you are able to connect an external mic to your camcorder. But now, the type of video you are shooting is going to dictate the kind of mic you use.

Spoken Word/Single Speaker
In this application, the speaker is either sitting or standing and speaking directly to the camera, maybe telling a Bible story, reciting a piece of Scripture or preparing a short video for your church’s website.

Indoors: The best mic choice is a lavalier for a single speaker, since the subject’s hands are free to gesture. It also eliminates the risk of holding the mic incorrectly. If the subject is seated, a handheld mic on a short stand or a boundary microphone on the floor can work well in a quiet room. This is a good option when recording children or subjects who are nervous, and who may touch or play with a lavalier mic.

Outdoors: You’ll need a unidirectional mic to cut down on background noise, with an effective windscreen to prevent wind noise. Here are three choices:

• A unidirectional lavalier mic.
• A handheld unidirectional mic on a mic stand off camera.
• A shotgun mic on a boom.

"Man on the Street" Interviews
Let’s say you want to capture reactions from members of various ministries or record comments from teen campers. Since you’re the videographer and the sound crew, how do you capture your questions and your subject’s answer? If another person will serve as "reporter", have them use a handheld omnidirectional microphone. This will pick up just enough background ambience to set the scene. If you’re working alone, clip a lavalier mic onto the subject, and a second lavalier on yourself to pick up the questions that you ask.


Church Service
Recording audio for a church service is one of the easier tasks that you’ll encounter. All you really need is a connection from the sound system to your camcorder. In this scenario, all the mics and cables you need are already in place. And since we’ve devoted an entire issue of Shure Notes to this subject, including helpful information on low-cost recording equipment, we’re going to send you there now.