Controlling the Recording by Barb Karg, Rick Sutherland, & Jim Van Over
While most professional audio recording equipment is designed for ease of use, it's important for the sound recordist to constantly monitor the recording for the best possible quality. This monitoring system requires the use of several different pieces of equipment, including a volume unit meter, peak program meter, and a host of additional mixing and cabling devices.
Volume Unit Meter
The volume unit, or VU, meter measures signal amplitude as an approximate average. The meter is marked with a red or black area to indicate when distortion occurs. When recording any sound, it's the goal of the recordist to avoid distortion. Since the VU meter measures an average, it's best to keep the indicator as close to the distortion area as possible without crossing into it.
When using a radio microphone on location, be sure to check for nearby power lines or broadcast sources on the same frequency. You don't want your romantic and elaborate outdoor wedding scene to be interrupted by the crackle of a railroad dispatcher.
Peak Program Meter
The peak program meter, or PPM, measures the peak signal level. This means the indicator should be allowed to cross into the distortion area without being allowed to “peg” all the way to the right side of the meter. That would indicate signal distortion.
Deciding Whether to Mix
All this talk of watching the needle and keeping it within a specific range doesn't mean the recordist continually adjusts the volume controls. Also called potentiometers or pots, these should be set during a volume test before filming begins. Once set, there should be no need to adjust them while recording. Doing so can result in unwanted fluctuations, making it difficult to match sound during editing.
Cables and Connections
Most recording problems during filming arise because of defective or incompatible cables or connections. If one piece of equipment has DIN plugs and the other requires XLR connectors, a lot of time and money can be lost while the correct equipment is tracked down. A difference in impedance can also create difficulties when recording. If your microphone and your recorder have different impedance levels, distortion can occur. While some recorders have a variable impedance switch, it's easier to check beforehand to confirm that the equipment is compatible. A ratio of five-to-one is acceptable. It's always a good idea to keep several cable adapters in your recording kit to quickly and easily avert an audio disaster.
