Live Recording Microphone Tips
Engineers spend their whole careers building a library of techniques for recording live performances. Microphone placement and selection are key elements of a successful recording.
Mic Placement Mic placement is the single most important criteria in determining the quality of a live acoustic recording (other than the performance, of course!). Experimenting with microphone placement in a given acoustical space is critical; good placement is very time consuming compared to setting up the recording rig. Because every acoustical space is different, it is important to record several test tracks before recording final material. With a large sound source such as an ensemble make certain mic placement can capture the whole of the source without being too close. Often, a stereo pair 5 ft above and 5 ft back from a conductor's position is used as the master pair. A tall (15+ foot) microphone stand is an essential accessory for live recording since getting microphones above floor level will get them away from unwanted sound sources. Also, since many acoustical instruments radiate up and out, getting microphones high helps capture them. Hanging microphones is often a solution, but is time consuming and cabling can be unwieldy. The master pair is often a mid/side pair (cardioid/bi-directional), coincident cardioids, or near coincident cardioids. The master pair receives mostly direct sound versus reverberation, and properly places the instruments in the stereo field. If additional ambience is desired, spaced omnis located throughout the performance space, high in the balconies can be mixed in with the master pair or recorded separately. Artificial reverberation in post production is a compromise when acoustical ambience cannot be captured. When recording individual sound sources, closer placement results in more direct versus reverberant sound. A mic placed too close can result in "hot spots" with too much emphasis in one frequency band. For instance, when recording acoustic guitar, microphones placed close to the guitar body will result in a tubby, unnatural sound, since the instrument radiates sound from the entire length of the instrument, not just the body.
Mic Selection Today, there are scores of excellent microphones for live and studio recording. Microphones are available in a variety of form factors and electrical characteristics. Different microphones yield quite different audible results. Microphones are very much like musical instruments; each one has its own unique characteristics and appropriateness for different applications. Microphone selection is a personal choice and experimentation is most important. Sound Devices mixers and recorders have high-performance (high bandwidth, low distortion) microphone preamplifier circuitry that can accept virtually every professional microphone. Their balanced, low-impedance inputs can provide 48-volt phantom power for microphones that require power. Condenser Microphones — Most microphones used for live recording are high-sensitivity condenser microphones. These mics use the phantom voltage from the mixer or preamplifier to power their output amplifiers and impedance converters. Some condenser microphones require 48 volts to operate while others can work at any voltage from 12 to 52 volts. Sound Devices mixers and recorders will power the majority of them. Condenser mics are found in a wide variety of physical types, including probe style, side-address, shotgun, lavalier, and headworn. Their low-mass diaphragms are available in a large variety of sizes. Condenser microphones can have very high sensitivities, making them appropriate for recording distant sound sources. For critical 24-bit recordings, microphones with the lowest self-noise should be considered. Microphone self-noise can show up when recording highly dynamic content. Unfortunately, very quiet microphones are expensive. Dynamic Microphones — Dynamic mics are generally simpler, less expensive, and more rugged than condenser microphones. Because they do not have amplifier circuitry their sensitivity is often less than condenser mics. Phantom power has no effect on dynamic mics. Older dynamic microphone designs, some of which are still excellent microphones, have low sensitivities and require high levels of preamplifer gain. Ribbon microphones, a subset of dynamic microphones, generally have even lower sensitivity. With distant sound sources and low gain preamplifers, many of these microphones don't have enough output to attain usable levels. Additional amplification may be needed. Remember, a well placed less expensive microphone will improve your recording substantially versus improperly placed expensive mics.