Whether it is a classical ensemble, big band or other group of acoustical instruments, recording an entire ensemble can yield professional results if certain things are kept in mind. This article explores some ideas that may help to get the desired professional results.
Main Stereo Pair
The main stereo mic pair captures the essential blend of the entire ensemble and the room acoustics. Because this pair of microphones is at a considerable distance over and in front of the ensemble, room acoustics will be noticed as a significant component of the overall sound. A stereo microphone may be used, or two well-placed omni directional condenser microphones. The idea is to find the best spot for the pair to capture the overall sound which will be influenced by the room acoustics. If the room is too live, the sound will sound mushy and ill-defined. If the room is too "dead", the sound will not be very impressive, but and possess a very dry characteristic. Liveness is increased by increasing the distance to the ensemble (hanging or placing the stereo pair higher in the room and further from the group. Liveness is reduced by bringing the mics closer to the group (more direct sound, less room sound). By taking the time to experiment with this position, one can achieve a good sound without alot of multi-micing (putting mics on each instrument), which creates phase problems between the various microphones, and the overall blend of the instruments may sound unnatural when using just single mics. One can always add some reverb to the stereo pair signal to add liveness and depth later, but a soggy sound produced by thin and distant sounding instrument is often a sign of room acoustics that were too live, or mic placement that was too far from the source. If the room acoustics are not very pleasing, it is best to try to deaden the room and liven up the sound with reverb and effects later.
Some microphone stereo placement techniques include the X-Y stereo pair, the M-S (middle-side) stereo technique and positioning a stereo mic. Usually an omni (circle) polar pattern is selected on the mic to capture the room sound and the ensemble with minimal phase interference caused by the releced sound arriving at the rear of the mic. Condenser mics are used most often in this main mic position. They usually require phantom power from the preamp or mixing console. Cardiod mics such as the shure SM57 are great live vocal mics or guitar amplifier mics, but are not suited for micing an ensemble because of their "proximity effect". This means that the bass or low end of a sound increases the closer you get to the mic, and the frequency response and noise characteristics of these type of mics are not suited for the application of main stereo room micing.
That leaves the actual instrumental blend, which should be achieved with the louder instruments to the rear, and the softer instruments in front. The actual physical placement of the musicians and instruments can also form a "mix" on the stereo pair. The more work that is put into getting the right sound with just one stereo pair, the better off the sound will be when individual solo instrument mics are added, or even spot mics to pickup certain sections or clusters of instruments that need to be highlighted and added to the stereo pair's main signal.
The actual signal path of the stereo pair should be the high quality stereo mic or microphone pair into a stereo pre-amp using high quality (thicker) XLR balanced microphone cable and then straight to the recording machine or analog to digital converters if recording on digital medium. This bypasses all of the noisy electronics that may be producing unwanted distortion of the sound or creating a higher noise floor which may be disturbing on soft passages. By creating a direct path to the recording source and monitoring the sound off of the recorder, one can achieve pristine results. Most professional mixer input modules will not adversely affect the signal if used to route to a multitrack recorder, but using the direct method bypassing a mixer and it's electronics and going straight to the recorder will yield a cleaner sound.
As with any recording techniques, there is no holy grail, but only using high quality components and actually listening to the end result, making changes to improve the sound. Listening is actully the best tip for achieving a great sound.
Equalization, Effects, Reverb and other signal processing can be applied in the mixing stage to spruce up the recording even more. But that gets into mixing, which we address in a future article.
A recommended book on mic techniques featuring stereo pair and individual mic placement recommendations for further reading.
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Professional Microphone Techniques