Stereo Microphone Techniques
One of the most popular specialized microphone techniques is the stereo microphone technique i.e. using two microphones.
Stereo miking is a great way to increase the sense of depth in a mix, giving that more quality sound.
There are no rules or limitations when using the stereo microphone technique. Ultimately it is down to imagination and experimentation.
Always be aware of phase cancellation when using the stereo microphone technique. Phase cancellation occurs when two signals of the same frequency are out of phase with each other resulting in a net reduction in the overall level of the combined signal. If two identical signals are 100% or 180 degrees out of phase they will completely cancel one another if combined. When two signals are slightly out of phase you will notice a warble in the recording - this is not evident when the two signals are panned hard left and right so always check the signal in mono.
For tips of best practices when recording, check out the Recording Considerations article.
There are essentially four main procedures for stereo miking, with each having their own variations, including:
Microphone Type: 2x cardioid or omni-directional
The space paired technique is the easiest of all the stereo microphone techniques and is simply two microphones placed in front of an instrument, with one being placed to the left and the other to the right.
The distance between the two microphones can vary between 0.2 meters to 10 meters. The exact distance is usually determined by the size of the instrument, the size of the room and how many instruments are being recorded.
The spaced pair technique can obtain a large stereo image providing a bright open sound. There is however a drawback to this technique. Often there is the potential for phase cancellation and comb filtering due to the difference in the arrival of the sound to the two microphones. To help eliminate the problem of phasing, keep both microphones at exactly the same height and distance from the instrument. A mono reference source can be used to check for phase problems.
The spaced pair technique can be used with omni, but mainly uni-directional microphones.
Microphone Type: 2x cardioid
The X-Y technique involves a pair of cardioid microphones of the same make and manufacture placed with their heads facing as close together as possible at an angle of around 90-110 degrees.
The midpoints of the two microphones should be pointing towards the source, with the outputs being equally panned left and right. The two microphones should be placed within close proximity to the sound source.
The coincident technique produces a relatively narrow stereo spread but good imaging. Due to the microphones close proximity, there are no phase problems as can be seen with the spaced pair technique above.
A variation on the coincident technique is the near-coincidental technique where a pair of cardioid microphones are angled out at between 90-120 degrees. The bottoms of the microphones should be almost touching and head about 20cm apart.
Microphone Type: 1x cardioid, 1x bi-directional
The mid-side configuration combines two types of microphone, one being either a cardioid or omni directional microphone (the mid), and the other being with a figure-eight microphone (the side). The cardioid/omni microphone is placed in the middle facing straight forward, while the figure-eight microphone is placed facing ninety degrees to the side.
The technique provides good stereo spread, stereo imaging and localization. The configuration can usually be placed on a single microphone stand.
Microphone Type: 2x omni-directional
The binaural configuration is less common than the other three techniques and is used to replicate the way our ears capture sounds, and replay those sounds directly into the corresponding ears.
The arrangement places omni directional microphones on a ‘human head’ while recording. The attempt is to accurately recreate the way a human hears.