It's really hard to get single keystrokes to fire Macros reliably in any App. As @Sleepy says, the usual approach is to look for a menu condition that changes when you are typing text, in order to disable the macro when you are in a text field. (And on my inspection of Logic Pro there is no such change in the menu when typing text that I could find.)
The single letter hotkeys that are built into Apps (like "R" for record in Logic Pro) have been designed to work this way but that is because they are built into the Apps at some fundamental level.
The inbuilt single key hot keys are usually for doing one single action or changing the state of something (like "A" to change the mouse cursor to a selection tool). They are not for complicated multi-step actions that could be damaging if the single key was pressed by accident.
If the single key hot key you are trying to make is to simply invoke an existing function that already exits in the menu, you can make your own custom single key hot key using Mac System Preferences or very often in the App itself.
The problem with the single key approach with firing Keyboard Maestro Macros is that if you have many Macros that do things (in say, Logic Pro) how are you going to remember all those single keys? It's very likely that you will fire Macros by accident even if you get the "not in a text field" condition to work.
For what it's worth my approach to App specific Macros is to make use of Keyboard Maestro's floating Palettes. The Palettes can be shown and hidden with a hot key (in my case I always the same hot key ⌥⌘K to show/hide the Keyboard Maestro Palette for whatever App I am in). The Palettes are easy to click on to fire the Macros, they give a visual reminder of whatever the hot keys are and I can make custom Icons that make finding my Macros very easy. Nothing to remember - which is especially good if I am not using the App every day.
