One of the first things you should know is that most (though not all) of Logic’s internal controls respond to Fader data, rather than MIDI controller data. To be able to control just about any fader in Logic using an external MIDI controller device, you will need to create the appropriate Transformer objects in the Environment.
In the following example, I have a MIDI controller device connected to Logic’s Physical Input. This could be any kind of device, but let’s say it’s the Behringer BCR2000.
I’ve created an Audio Object and inserted the ES1 audio instrument. I’ve attached a Monitor object to it, so I can determine which knob sends which kind of fader data. The same data can be used to control the knob! In this case, I need fader number 10 on channel 2 to control the filter cutoff.
Finally, I’ve inserted a Transformer object between the Physical Input and the Audio Object. Take a closer look at the picture. The Transformer transforms incoming MIDI controller data to Fader number 10 on channel 2.
Now I can turn a rotary on the BCR2000 to send controller data to Logic, which is translated to fader data and fed to the ES1. Pretty cool.
Note that you will probably want more fine-grained transformations instead of translating all controller data. The above setup is just an example.