Mid Side Recording Explained

Mid-Side recording represents a uniquely flexible stereo technique that allows width adjustment after the recording session. Unlike conventional stereo that commits to a fixed width during recording, Mid-Side captures the components needed to create variable stereo width during mixing.

The Mid-Side Concept

Mid-Side recording uses two microphones with specific polar patterns. The mid microphone, typically a cardioid, points directly at the sound source and captures what would be the center of a conventional stereo recording. The side microphone, always a figure-8 pattern, positions perpendicular to the mid microphone, capturing sound from left and right while rejecting sound from front and back.

These two signals don’t create stereo directly. The mid channel sounds mono, and the side channel sounds ambient and hollow on its own. Combining them through a decoding process creates usable stereo with adjustable width.

The technique’s power lies in this separation of center and side information. Boosting the side signal widens the stereo image. Reducing it narrows toward mono. This control exists in post-production without degradation, providing unprecedented flexibility.

Microphone Setup

The mid microphone positions facing the sound source at the recording distance and height determined by the source characteristics. Cardioid patterns work most commonly, though hypercardioid or omnidirectional patterns create different results.

The side microphone positions as close as possible to the mid microphone capsule, oriented perpendicular so its null points face the sound source and away from it. The figure-8’s sensitive sides face left and right, capturing the ambient field.

Physical microphone mounting requires attention. Clip-style shock mounts allow positioning two microphones very close together. Specialized Mid-Side mounting bars hold both microphones in proper alignment. The goal involves positioning the capsules as close together as practical.

Decoding Process

Decoding converts the raw Mid-Side signals into conventional left-right stereo. The process involves duplicating the side channel, inverting the polarity of one copy, then combining the original side with the mid for the left channel and the inverted side with the mid for the right channel.

Most DAWs include Mid-Side decoder plugins that automate this process. Alternatively, manual routing accomplishes the same result: duplicate the side track, flip its polarity, pan the original side left and the inverted copy right, then blend with the centered mid track.

The width control comes from adjusting the level of both side channels relative to the mid. Higher side levels produce wider stereo. Zero side level produces pure mono from the mid microphone.

Mono Compatibility

Mid-Side provides perfect mono compatibility by design. When left and right channels sum to mono, the opposite-polarity side signals cancel completely, leaving only the mid signal. This mid signal represents a focused, mono-compatible recording without phase issues.

This characteristic makes Mid-Side valuable for broadcast television, where many viewers still hear mono audio. Film production benefits similarly, ensuring center dialog remains clear regardless of playback configuration.

Even stereo-focused music production benefits from guaranteed mono compatibility. Club sound systems, mobile phone speakers, and other mono playback situations remain common enough to warrant consideration.

Application Advantages

Acoustic instrument recording benefits from Mid-Side flexibility. Capturing piano, acoustic guitar, or string instruments with Mid-Side allows dialing in the perfect width during mixing when the full arrangement context exists.

Drum overhead recording using Mid-Side provides width control over the kit image. Narrowing the width focuses the drums in the center, while widening creates an expansive kit picture.

Room microphone applications suit Mid-Side well. Capturing room ambience with adjustable width allows tailoring the spatial characteristics to match close microphone sources during mixing.

Limitations and Considerations

Mid-Side requires a figure-8 microphone for the side channel. Ribbon microphones provide natural figure-8 patterns, while many large-diaphragm condensers offer switchable patterns including figure-8.

The technique captures rear room sound through the side microphone’s rear lobe. In problematic acoustic spaces, this rear pickup introduces unwanted reflections. Mid-Side works best in controlled acoustic environments.

Processing Mid-Side recordings requires understanding the decoding chain. Applying effects to the encoded signals produces different results than applying effects after decoding. Experimentation reveals which approach suits specific situations.