Overcoming Problems with Stereo Miking
When you do stereo miking in your home recording process, watch out for phase cancellation and poor stereo imaging. These are thorny issues but they have simple solutions.
Phase cancellation happens when the two microphones are placed so that they each receive the sound at slightly different times. When this occurs, you don’t hear the bass as well because the low frequencies drop off. Improper mic placement or two mics that are out of phase with one another can cause phase cancellation.
Most digital recorders have a phase switch that allows you to reverse the phase of the signal (even after it’s recorded). To test whether two mics are out of phase, just reverse the phase on one mic (don’t do both) and listen to see whether the low frequencies become more apparent:
If they do, you’ve corrected the problem and you’re good to go.
If this doesn’t correct the problem, try changing cords on one of the mics because some mic cords are wired differently than others.
If this doesn’t work either, you need to adjust the relationship between the two mics. Just move one mic around a little and listen for changes in the bass response. When the missing bass appears, you know you’ve solved the problem.
Poor stereo imaging
Poor stereo imaging occurs when you can’t tell where things fall from left to right (or right to left, if that’s the way you think), or when you can’t hear a clear center point in the sound. Poor stereo imaging is a little more difficult to correct than phase cancellation, but you can fix it.
The solution depends on the stereo-miking technique that you use. If you use the X-Y technique, you’ve probably placed your mics too close to the sound source. If you use the spaced-pair technique, you’ve probably placed the mics too close to one another in relation to the distance from the instruments. In either case, adjusting the placement of your mics should clear up the problem.
A Jecklin disk is a simple device that can make dealing with these issues much easier (and give you a pretty realistic stereo image for not a lot of money). A Jecklin disk is a 1/4-inch-thick round plate, approximately 12 inches in diameter, with 1/2-inch foam attached to both sides.
Omnidirectional small-diaphragm condenser mics are placed on either side of the plate at precise locations and this entire unit is directed to the sound source. To learn more about the Jecklin disk, do an Internet search and you’ll find plenty of hits — including some plans to build one for under $30.