The A/B stereo recording technique, aka Spaced Pair, captures the same sound source through the two microphones it has within. These mics are located from a range of three to ten feet apart from each other. In turn, the separation creates time-of-arrival (phase) and level (amplitude) differences from the input they receive. As they get closer, the differences will be more obvious. Regardless, the A/B stereo recording technique is extremely efficient when creating wide stereo images inside a studio.
A/B Stereo Recording: the Fundamentals
Time-of-arrival and level differences usually recreate the signals we receive through our ears. Specifically, they simulate the way our brain uses them to position the sound sources within the horizontal spectrum. In order to achieve the a/b stereo recording effect, we must pan the mic tracks to the left and to the right. The mix of both signals produces extreme effects. However, time-of-arrival differences might create phasing in the output when the mic is not panned this way, as well as variable degrees.
Regarding the Microphones
The A/B stereo recording technique is able to use diverse types of microphones, cardioid and omnidirectional being the most common ones. Spaced cardioid mics should point directly at the sound source in order to generate narrower or broader stereo images. This setup won’t capture much of the room acoustics, though. You can position the omnidirectional microphones in the same way, for they tend to produce a broader and more diffuse stereo image. This setup’s purpose is to capture a more realistic acoustic environment.
Examples
This technique is widely common when miking drums, in full bands, and for capturing room sound. In order to avoid an uneven diffusion on the mics, it’s important to locate the microphones symmetrically within the acoustic space. Positioning the spaced pair halfway from low-frequency sources allows us to focus on the low frequencies. As an example we have bass guitar cabinets and kick drums.
