Pan Laws Detailed (With a Cautionary Tip)

[fader8]

I had made these measurements some time ago, but the subject keeps coming up, so I thought I'd annotate them and post the results for everyone.

 

Logic Pro 7 has three pan laws: 0dB, -3dB and -3dB Compensated. The graph below is the level change for the LEFT channel with an automated left to right track pan.

 

Whether you use the -3dB Compensated, or the 0dB law is your own preference. But beware if you use the -3dB uncompensated. Should you choose to use busses to subgroup tracks, the level of those tracks will all drop 3dB! Even though you haven't touched the faders!

 

From left to right is time, (0-10 sec's) and the vertical axis is dB.

(Note that pan center is the spot where the blue trace and the yellow trace meet)

[Agzilla]

"Should you choose to use busses to subgroup tracks, the level of those tracks will all drop 3dB! Even though you haven't touched the faders!"

 

 

Why does this happen? Is it the individual tracks being sent that drop level or the group pf tracks playing through the bus itself?

[David Nahmani]

Here is my little quick tutorial on pan laws:

 

0dB is the default setting, it doesn't compensate anything, so the result is that if a signal is panned in the center, it stays at its nominal level (0dB of gain), and as you pan a signal to one side, the level drops.

 

-3dB is, in my opinion, a first attempt at 'fixing' that 'problem', by gradually reducing the gain of the signal as you bring it back to center, ending up at -3dB when panned dead center. Not an ideal solution, but the advantage is that the level remains constant as you pan the signal across the stereo field.

 

-3dB compensated is the best of both world: using the -3dB setting but adding 3dB of gain to the whole signal. So it's pretty much raising the gain as you pan to a side, so that the level remains constant as you pan across the stereo field, but not losing -3dB when panned center. The level is consistent as you pan, although you'll see the level rise on the meters as you pan to a side.

[woodenboy]

And where do you set your preferences for this?

[LukeDunn]

File>Song Settings>Audio

 

 

Luke

[Nado]

Also this setting is song specific, so save it in your autoload if you want to use it all the time.

[woodenboy]

Great, thanks

[fader8]

Why does this happen? Is it the individual tracks being sent that drop level or the group pf tracks playing through the bus itself?

 

The change seems to happen within each fader object itself. You can see this if you switch to -3dB, monitor a tone on a track and watch the meters for the track and the bus and the output channel. Now switch between pre and post fader metering. See what I mean?

 

Now switch back to -3dB compensated and everything will work as you'd expect it to, ie you get exactly the same levels on the track, bus and output regardless of pre or post fader meter setting, (assuming you've left all the faders set to 0)

 

As to why it does this? No good reason I can see. The solution? Just use the -3dB compensated pan law and you won't have to think about it.