Panning is a useful way of creating both size, and separation in a mix.
All music used to be in mono. One of the major defining characteristics of modern music is the fact that it’s in stereo.
If you listen to an old jazz recording from the 1930’s, you will notice how everything is in the center and sounds “smaller”. Listen to some of the Beatles and all of a sudden you hear certain vocals playing in one ear, when other elements of the music are in your other ear. Music being done in the era of when stereo was at its infancy, gave way to some really interesting sounding mixes. Engineers and artists began using panning as a creative tool, and it’s still being done to this day.
Everything around you that you hear with both ears, you hear in stereo. This is simulated in audio by the use of 2 channels: a left channel and a right channel.
In your Daw, your pan knob is usually located above your fader, and allows you to send that channel to a combination of the left and right channels.
When something is panned in the center of a mix, it feels mono. Your kick drum or bass might sound great staying in the center of your mix, so that you can use the rest of your stereo field for other elements in your mix.
If you have a stereo piano, the sound will change dramatically being in mono (both sides of the piano equally going to the left and right channels) versus being in stereo (left side of the piano in the left channel only and the right side of the piano in the right channel only). The difference to our ears is: in mono the piano sounds small and condensed, opposed to the stereo version where the piano has width, depth, and space.
Many times in acoustic rock, we like to record two separate passes of acoustic guitar, because we are anticipating that in the mixing process we are going to pan one of the guitars all the way to the left (hard left) and the other all the way to the right (hard right). The result is extremely powerful.
Ultimately there is no “rule.”
There are many common practices out there, but no one has ever won a Grammy simply by “following the rules of panning”.
So make observations and listen to a ton of music. Notice the patterns and trends within the different genres. For example: you are going to hear in 99% of music that the kick drum will be panned in the center of the mix. Bass instruments will normally follow a similar pattern. Percussive elements like hi-hats, cymbals, shakers, and tambourines can be anywhere in the stereo field.
Experiment with subtle panning to make certain instruments “sit” in the mix and to give the listener a more interesting listening experience.
One common myth is: you can duplicate an instrument, and simply pan the original to the left and the copy to the right. This will only result in a mono outcome. 2 IDENTICAL signals will only create a louder, mono signal because of identical frequency and phase (timing) content. This is why in my example with the acoustic guitars, there were two separate recordings/performances, not just a copy of one.
You can use a variation on this technique by delaying ONE of the copies by a few samples/milliseconds (they need to be panned to the left and right). Experiment with delaying the copy by a slight amount, and then a more extreme amount, and observe how the perception of width increases by increasing the delay of the copy. If you do it too much you will start hearing an actual delay (timing difference) of the copy (this will happen around 30 milliseconds). Read about the Haas effect.
It’s for these reasons that we choose to “double track” or record a second pass of an instrument playing the identical part, so that we have the option of panning “hard left and right” in the mix.
Panning is just one instance of the growth of sonic quality in a very young industry of audio. Think about it, we are just under 100 years old. I believe that the next wave of music will be a 360 degree experience. But who knows?! I look foward to what the future holds!