Stereo Recording Techniques

Stereo recording creates the perception of width and spatial dimension by capturing sound with two microphones. The differences between left and right channels, both in timing and level, fool the ears into perceiving sounds across a horizontal soundstage rather than from a single point.

Coincident Techniques

Coincident stereo places two microphone capsules at essentially the same point in space, angled apart to create directional differences. The XY configuration represents the most common coincident approach, positioning two cardioid microphones with capsules nearly touching at angles between 90 and 135 degrees.

The XY technique produces perfect mono compatibility since both microphones capture sound at the same time from the same location. No phase differences exist between channels, preventing frequency cancellation when summed to mono.

The trade-off involves narrower stereo width compared to spaced techniques. XY recordings sound focused and centered rather than expansive. This characteristic suits broadcast applications where mono compatibility matters and intimate recording situations where extreme width feels unnatural.

Near-Coincident Techniques

Near-coincident techniques separate microphones slightly while maintaining close spacing. ORTF, developed by French broadcasting, positions cardioid microphones 17 centimeters apart at 110-degree angles. This configuration mimics human ear spacing and angle.

ORTF provides wider stereo imaging than XY while maintaining good mono compatibility. The slight spacing introduces minimal timing differences that enhance spatial perception without problematic phase interactions.

NOS technique spaces cardioid microphones 30 centimeters apart at 90-degree angles. This wider spacing produces more expansive stereo than ORTF with somewhat reduced mono compatibility. The technique suits orchestral and ensemble recording where natural width serves the music.

Spaced Pair Techniques

Spaced pair configurations position microphones several feet apart, creating significant timing differences between channels. Sound arriving from one side reaches the nearer microphone measurably sooner than the farther microphone, producing strong directional cues.

AB stereo uses two omnidirectional microphones spaced three to ten feet apart. The omnidirectional pattern captures a natural frequency response without proximity effect issues. Wide spacing creates an expansive stereo image with excellent low-frequency capture.

Phase considerations require attention with spaced techniques. The timing differences that create width also cause frequency cancellation when summed to mono. Spaced recordings may sound thin or hollow in mono playback.

Mid-Side Technique

Mid-Side uses a cardioid microphone facing forward (mid) combined with a figure-8 microphone facing sideways (side). Decoding the side signal creates left and right channels with adjustable width controlled by the side signal level.

The unique advantage of Mid-Side involves post-recording width control. Increasing the side signal widens the stereo image. Decreasing it narrows toward mono. This flexibility proves valuable when the optimal width isn’t known during recording.

Mid-Side provides perfect mono compatibility since the side signal cancels completely when summed to mono, leaving only the cardioid mid signal. This characteristic makes Mid-Side valuable for broadcast and film applications.

Blumlein Technique

The Blumlein configuration uses two figure-8 microphones positioned coincidentally at 90 degrees. This arrangement captures a three-dimensional representation of the recording space including significant rear pickup.

The figure-8 patterns reject sound from 90 degrees off-axis while capturing front and rear equally. This creates a distinctive sound that includes substantial room ambience from behind the microphone array.

Blumlein excels in well-designed acoustic spaces where the room sound enhances the recording. The technique works poorly in problematic rooms since rear reflections capture as prominently as front sources.

Application Considerations

Source characteristics influence technique selection. Wide sources like orchestras or drum kits benefit from spaced techniques that capture full width. Focused sources like solo instruments or vocalists suit coincident techniques that provide intimate imaging.

Room acoustics play significant roles in technique selection. Live rooms with desirable ambience suit techniques with broader pickup patterns and wider spacing. Dead rooms or problematic spaces benefit from coincident techniques that minimize ambient capture.