Have you ever wondered why, when you place a mono clip in a stereo timeline, or a stereo clip in a mono timeline, there’s a difference in audio levels? The reason is the “Pan Law” (or the “Pan Rule”).
This “is a recording and mixing principle that states that any signal of equal amplitude and phase that is played in both channels of a stereo system will increase in loudness up to 6.02 dBSPL, provided there is perfect response in the loudspeaker system and perfect acoustics in the room.” (Wikipedia)
In other words, “adding two identical signals [i.e. left and right channels] results in a 6 dB (6.02 dB actually) volume increase.” (Steinberg.net)
Because perfection is almost impossible to achieve, many audio consoles and audio software apply a -3 dB audio level change as a sound is panned from left or right (playing solely out of one speaker) to center (playing equally out both left and right speakers). In other words, the volume of a mono sound playing out a single speaker (panned fully left, for example) will be amplified +3 dB louder than the same sound panned center and playing out both speakers.
“The whole idea in the first place of “pan laws” and dipping the level in the centre of a pan pot, was that when people were doing those wild pans that had the guitar flying left to right all the time during a solo, the level of the thing being panned would seem to jump up and be too loud as it passed through the centre unless the centre was dipped….
“Theoretically, that -3 (or whatever) dip was chosen so that when you move a signal from far left into the centre it should appear to be about the SAME level, without adjustment. In practice, you adjust and once you HAVE adjusted, the amount of that dip built into the panner doesn’t matter anymore until you move the position again.” (Gearslutz)
This is the reason when you place a stereo clip on a mono timeline, it is about 6 dB too loud (+3 dB per channel), or that a mono clip placed into a stereo timeline will be about 6 dB too soft.
The amount of gain or loss can vary by audio console and the acoustics of the room. “Other common pan laws are -2.5dB, -4.5 and -6dB at center.” (Recording.org)
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