What is pan?
Pan is the control that adjusts where in the stereo field a sound is heard between left and right. The name is short for panorama, and in a DAW it appears as a knob on the channel strip. Center is shown as C, left as L, and right as R, and pushing a sound fully to one side is called hard panning.
Why you use pan
If every instrument sits in the center, sounds overlap and the parts can become hard to tell apart. Placing guitars, backing vocals, and percussion to the left and right creates stereo width while securing space in the center for the vocal, kick, and bass. There is no single correct placement, though.
Pan and balance
Panning a mono signal decides in what proportion one signal is sent left and right. Balance, used on stereo signals, basically changes the relative level of the left and right channels that already exist. Behavior differs by DAW and by pan mode, so check the displayed name when you work with stereo material.
Check in mono too
A mix spread wide can give a different impression when it is played back in mono on a smartphone or a small speaker. After you decide your pans, it is safer to check now and then that the main parts are still audible in mono.
What is pan law?
Pan law is the mechanism that compensates for the level change as a sound moves to the center or to the sides. So that a centered sound coming from both speakers does not feel too loud, the DAW applies a set amount of adjustment. The setting changes how a pan move sounds, so judge by ear and not only by the numbers.
Further reading
How to control volume and pan for several tracks at once is introduced in the summing stack section of Handy tips for organizing tracks in Logic Pro (Japanese).
