The A/B stereo recording technique, also known as Spaced Pair, is designed to capture the same sound source through the two microphones they have within. These mics are located from a range of three to ten feet apart from each other, which allows them to create time-of-arrival (phase), and level (amplitude) differences from the input they receive. As they get closer, the differences will be more obvious.
Time-of-arrival and level differences are usually used to recreate the signals we receive through our ears and the way our brain uses them to position the sound sources within the horizontal spectrum. In order to achieve this effect, it’s essential that we pan the mic tracks to the left and to the right. Both signals should be mixed to produce extreme effects. It’s worth mentioning that time-of-arrival differences might create phasing in the output or variable degrees when the mic is not panned this way.
The A/B stereo recording technique is extremely efficient when creating wide stereo images inside a studio. This technique is widely used when miking drums, full bands and 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. This can be seen in bass guitar cabinets and kick drums.
This technique is able to use diverse types of microphones, being cardioid and omnidirectional 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. The omnidirectional microphones can be positioned in the same way and they tend to produce a broader and more diffuse stereo image. This setup is meant to capture a more realistic acoustic environment.