To the average Jane making a film in her attic in Cleveland, the concept of sound and all the equipment involved in sound recording and mixing can appear overwhelming. But if you break down the components and examine their various functions in context, you'll find that sounds are a fascinating study. When it comes to your film and recording sound, the microphones are your ears, the recorder serves the function of your brain, and the tape is your memory.
On consumer-level tape recorders, there are three heads that read across the tape. One erases any existing data while the other two record and play back new information. Professional recorders, however, also have a synch head for laying down a synchronization track, which allows the camera and recorder to be timed together. Professional recorders will also have either a volume unit (VU) meter or a peak program meter (PPM) to aid in setting the appropriate input levels.
Digital and Analog Sound
Most film recording is done using one-quarter-inch (6mm) analog tape or the smaller digital audiotape, commonly called DAT. Various qualities of analog tapes are available, using different types of magnetic media. The aim is to get the best signal while reducing system noise and dropouts. The tape passes over the recording head at a rate of seven and one-half inches per second, allowing for fifteen minutes of recording on a standard reel. This process is slightly different for digital recording. Instead of recording the sound itself, a digital system records information about the sound's waveform. That information is fed to the playback unit, which recreates, rather than replays, the sound. This eliminates the system noise associated with analog tapes.
With some of the medium-priced digital equipment, the sound travels from the camera straight into a recording computer via an inexpensive high-speed connecting cable called FireWire. While budgetary concerns may make this an acceptable option, compressing the audio down to FireWire compatibility and then expanding it back again to edit the sound results in a loss of quality. The audio signal can be so degraded by the time it reaches the editing room that it's impossible to raise the volume without raising the system noise.
The company Sound Devices makes a good four-channel Time Code Recorder that records to a forty-gigabyte hard drive that's commonly used in the film industry. Fostex also makes a field recorder that features a time-code device.
Ideally, audio should go through a mixing board but then split off to a DAT recorder or hard drive recorder rather than to the camera that feeds the computer. This will mean using a time base corrector (TBC) that creates a time-code with the audio that corresponds with the video time-code. The audio is always best when left in multitrack form, then mixed, mastered, and married back to the video in the master-to-tape process.
There are almost as many types of microphones as there are opinions as to which are best. In the broad sense, microphone designs fall into one of two categories. Directional microphones will pick up sounds from a limited area. The designs vary depending on the pickup pattern or the shape of the area to which they are sensitive. These are extremely useful in settings with lots of background noise, such as a city street location, or in an interview situation when you want to hear the subject's voice clearly and distinctly without any ambient sound.
Omnidirectional microphones pick up sound in a nearly 360-degree sphere. This can come in handy for recording a conversation between two or more people around a table, for example. Assuming the rest of your set is as quiet as possible, a single mike can simplify filming (and keep equipment rental costs down).