Midside (M/S) mixing is a stereo audio recording and mixing technique that allows for greater control over the balance of sound in the stereo field. This method utilizes two channels: the mid channel, which contains information common to both left and right channels, and the side channel, which contains the differences between the left and right channels.

This channel is typically recorded using a cardioid microphone, capturing the sound from the front, which represents the main audio source (voices, instruments, etc). This channel can be recorded using a figure eight microphone or a pair of microphones arranged to capture the sound from the left and right sides, effectively capturing the ambient stereo information.

To convert the midside signal back to standard left right stereo, the mid channel and side channel are used together to create left (L) and right (R) signals: Left Channel (L) = Mid + Side & Right Channel (R) = Mid  Side. M/S mixing allows for greater flexibility in manipulating the stereo image. For example, the mid channel can be adjusted independently of the side information. It helps to create a wider stereo image without compromising the mono compatibility of the mix, as the mid information is central and can be mono compatible.

Engineers can widen or narrow the stereo field by adjusting the levels of the side channel. M/S mixing is commonly used in various audio production settings, including music recording, film sound design, and broadcasting. It can be particularly effective for mixing environments where spatial audio quality is critical. Overall, midside mixing is a powerful technique that provides audio engineers and producers with advanced tools for creating balanced and dynamic stereo recordings.