What is the typical panning law in stereo playback and how does it affect perceived level when panning?

• A. Unity panning with no level changes.
• B. Constant gain on both channels regardless of pan position.
• C. Equal-power panning keeps constant perceived loudness across the pan positions by adjusting the relative gains of left and right channels.
• D. Inverse-power panning reduces loudness toward the edges.

Answer: (C)

The key idea is how a pan law keeps the listener’s perceived loudness steady as you move a sound across the stereo field. In stereo playback, equal-power panning is the standard approach: the left and right channel gains are adjusted so that the total power stays constant as you pan. A common implementation uses L = cos(theta) and R = sin(theta), with theta ranging from full left to full right. This means L^2 + R^2 stays at 1, so the combined energy (and thus perceived loudness) remains roughly the same across the pan positions. At center, both channels contribute equally (about 0.707 each), giving the same overall level as a fully panned signal, just distributed between channels. If you used constant gains on both channels regardless of pan, there would be no actual panning effect on level. Inverse-power or other non-standard schemes would cause the perceived loudness to vary with pan, which is undesirable for smooth, natural spatial placement.