Before the modern era of the “one-man-band” in video recording, it was assumed that an audio operator was an essential part of the production crew. The reason was simple: to the audience, good audio is more important than the quality of the picture.
Nothing has changed, yet many camera operators now have the added responsibility to simultaneously acquire both the sound and image. To get this right is no small feat.
The key to high quality audio-for-video is a combination of the right tools and the human knowledge of how to apply those tools to the recording situation. Fortunately, life has gotten a bit easier, thanks to new audio technology now being adopted in the field.
Called 32-bit float recording, that new technology allows camera operators to record audio without worrying about setting levels. Don’t be confused. This is not turning on the camera-mounted microphone and setting the switch to “auto.” That old pot luck scenario for audio recording may have allowed the video operator to get by in the past, but it was never acceptable professional practice.
A number of companies now make 32-bit float portable audio recorders, including Sound Devices, Zoom and Tascam. Most video editing software and digital audio workstations can now play back 32-bit float sound. These field recorders allow the recording of useable sound no matter how the level is set.
The downside is 32-bit float audio files are about a third larger than standard 24-bit files. If distortion is introduced before recording — say an overloaded mic capsule or power line hum — 32-bit float won’t help. But in normal one-person shooting situations, these new recorders can save the distracted operator from getting over-modulated audio.
Of course, the video operator still needs to do correct mic placement and use the right mounting gear and wind protection when working in the field. These problems can’t be fixed with 32-bit float audio recording.
Just as with lighting, good sound recording demands a complex set of choices that used to be a full job in itself. Now it is often rolled into one. The challenge for the video operator is to become a generalist and learn the basics of good sound recording (and lighting) while wrapping those skills into the bigger picture.
For far too many videographers, the key microphone is the one built into the video camera. That assumption is a big mistake. Yes, the on-camera mic captures general ambient sound, but that’s about it. If you’ve ever heard an interview recorded this way, you know depending on the in-camera microphone is a major error.
There are five common physical microphone designs: handheld, lavaliere, shotgun, boundary effect and studio. Each type has a unique purpose in video recording.
The handheld microphone, commonly used for man-on-the-street news-style interviews, can be held by talent or mounted on a stand. Many models include integral windscreens and shock mounts that minimize the noise when the microphone is handled live. These microphones often cost under $100 and are essential tools for any video crew.
The lavaliere is the catchall term for a type of miniature microphone worn on the body. This microphone got its name from the cord that hung around the wearer’s neck. Current models are so tiny, they are almost invisible.
Lav mics are popular because they leave the wearer’s hands free and keep the microphone a fixed distance from the mouth. Most inexpensive lavalieres are designed for single-purpose use and suffer deficiencies when used away from the body.
A shotgun microphone has a long, tubular design that resembles a gun barrel. A mono shotgun is used to pick-up sound at a moderate distance from the source while rejecting sounds around the sides. Stereo shotguns can create a wider sound mix. A shotgun can be mounted on the camera or held by a separate sound operator.
The shotgun microphone — equipped with a blimp-mounted windscreen and shock-mounted on a “fishpole” boom — is often the prime microphone for video productions where a separate sound operator is involved.
The boundary effect microphone uses a large flat surface, such as a desktop or floor, to reflect sounds to the capsule. These reflected sounds, along with direct sound pickup, make the microphone more sensitive than other types at the same distance from the source.
Boundary mics are most useful in recording a stage play or the sound around a conference table. They can be mounted on walls or hung overhead on large flat panels to record choirs or other musical groups.
Finally, studio microphones, the largest microphones in physical size, are designed for stand mounting, usually with shock mounting accessories. These microphones are most often used for voice track narration, music recording or other applications where the highest quality is desired and microphone visibility is not an issue.
All mics have a transducer. For video production, the most common types of transducers are dynamic and condenser. The dynamic transducer consists of a coil of wire attached to a thin diaphragm. The coil is surrounded by a small permanent magnet. When the diaphragm is subjected to sound waves, it causes the coil of wire to move within the magnetic field. This movement creates tiny amounts of electricity in the coil.
Dynamic microphones are extremely rugged, available in many design types and require no external powering. They are also less sensitive and work well in poor acoustic environments. For this reason, dynamics are very popular in video applications.
The transducer in condenser mics uses an ultra-thin strip of plastic or metal tightly stretched above a piece of flat metal or ceramic (the backplate). The assembly is kept electrically charged. Together, the diaphragm and the backplate form an electrical device called a capacitor, which generates a change in voltage in response to sound waves. Since the electrical charges are very tiny, condenser microphones have internal preamplifiers to boost the voltage to usable levels.
Because of these internal preamps, condenser microphones provide a very high signal output. Today, there are two kinds of condensers: the low-cost back electret — in which the electro-static charge is applied to the back plate of the condenser — and the more expensive true condenser, which still requires an external polarizing voltage supply to the element.
All microphones have a directional pattern. This ranges from omnidirectional — equal pickup in quality and sensitivity in a 360-degree sphere — used in handheld microphones to a highly focused unidirectional pattern found in mono shotguns.
The directional characteristics are important to know when selecting the right microphone for a video shoot. For example, omnidirectional microphones (available in handheld, lavaliere, surface mount and studio units) have no proximity effect (bass buildup when the microphone is worked close to the mouth) and have lower handling noise than directional microphones.
However, when using an omnidirectional microphone there is no way to prevent undesirable sounds or room reverberations from being recorded. Use of an omnidirectional microphone is highly dependent on the recording environment. Unidirectional microphones, on the other hand, reject some background sounds.
For most video crews, having at least one good omnidirectional and unidirectional microphone is essential. This usually takes the form of a dynamic omnidirectional hand microphone and short unidirectional electret condenser shotgun.
However, as with most things in life, selection of a microphone doesn’t end there. There are also cardioid, super cardioid, hyper cardioid, bi-directional, hemispherical and hemi-cardioid pickup patterns on microphones. Each type is fine tuned to a specific application.
A good third microphone to own is a cardioid. With a heart-shaped pickup pattern, cardioids can capture sound in a 120-degree spread in front of the mic, gradually rejecting sounds in greater amounts to the rear.
Stereo Field Recording
It’s hard enough for one-person to get good mono audio, but we now live in the era of stereo and immersive surround audio. For multi-channel immersive recording, we recommend an experienced sound operator. For basic stereo, here are some tricks that can help a single person capture good sound.
The simplest way is M/S stereo recording, a technique that offers a bullet-proof way to acquire highly stable stereo sound images that are mono compatible. For video, M/S offers adjustable stereo width and perspective to match the picture on the screen. The sound field can be narrowed or widened in either the field or post-production suite.
The best part of M/S recording is that while it adds a dramatic sense of realism to video sound, it also provides an accurate monaural audio when the left and right channels are mixed, something not so easily achieved with other stereo recording techniques.
An M/S microphone uses two fixed position capsules, usually inside a single microphone body. A cardioid or hyper cardioid capsule (mid) faces the front of the microphone and is pointed directly toward the sound source, while a bi-directional or figure-eight capsule (side), is positioned at the sides, at right angles to the mid capsule.
The outputs of the two microphones are then routed through an adjustable sum-and-difference matrix, which extracts conventional, two-channel (left and right) stereo. For video production, it is usually best to avoid the matrix until post, allowing the editor to “paint” the sound to match the corresponding image on the screen.
Poor sound has been cited as the biggest killer on low-budget, independent video productions. It is the one part of the process that has not yet been combined successfully into the single operator production process.
If you are going to do any video production demanding complex audio, hire an independent sound operator with his own gear. Good sound can overcome poor video any day. The reverse is not true.