Stereo width
Also known as: stereo image, spread
How far a mix appears to extend to the left and right, which decides whether a soundtrack feels enveloping or stuck in the middle.
Updated
What it means
Stereo width describes the apparent size of the sound stage rather than the volume of anything in it. A wide mix places elements across the space between the speakers; a narrow one stacks them in the centre.
Camera audio is usually narrow whatever the specification claims. Two microphones a few centimetres apart on one body capture almost the same signal, so Stereo audio from an action camera is effectively mono with a little phase difference.
Music is where the width actually comes from in an action edit. A properly produced track has its own stage, and the camera sound sits in the middle of it rather than widening it.
How it works in practice
Keeping speech and low frequency content centred is the standard rule. A voice drifting to one side is distracting, and bass placed off centre loses the impact an Impact hit depends on on anything but a careful listening setup.
Width is then added around that centre by the music and by effects. A Whoosh panned across a transition uses the space that camera audio never fills, which makes a cut feel wider than it sounds.
Checking the mix folded down to mono is the discipline that catches mistakes, because anything that disappears in mono was relying on a phase relationship a phone speaker will destroy.
What to watch out for
Width enhancers usually work by introducing phase tricks, and those are exactly what collapses on a single speaker. The mix sounds impressive on headphones and thin everywhere else.
Over widening also empties the centre, which is where the content is. A spacious mix with nothing in the middle sounds large and says nothing at all, which is the opposite of what width was added for.
Platform encoding compounds whatever was fragile, because Platform recompression handles phase inconsistency poorly and the width a mix seemed to have does not survive the upload intact. What sounded spacious in the edit arrives flat.
How RawClip handles it
The music supplies the width and camera audio sits centred inside it, with speech kept in the middle so it survives a phone speaker. The mix is checked folded down to mono, because that is how a large share of viewers will hear it.