How to indicate window focus without being too subtle or too heavy handed?

My application has a window that shows the waveform of an audio sample and the text transcript of that audio:

Sometimes you want to navigate within the audio and sometimes you want to work on the text.

My intent is to allow focus in either of these panels, because each one has keyboard shortcuts that make sense in context. For instance, if you are in the audio panel and hit CTRL+Right, it moves the audio playhead forward 10 seconds, but if you are in the text panel and hit CTRL+Right, it moves the caret one word to the right.

If you look closely at the screenshot, you'll see that the audio panel has focus, indicated by a blue border. But my users are not looking closely, because I get reports that the app is "frozen".

It turns out that they think they are in the text panel and they are typing, say "A", and nothing happens, when in fact they are in the audio panel and "A" simply doesn't do anything in that panel. There are hotkeys to easily jump between the panels, but they don't realize that they need to use them to jump to the other panel.

So the question is: how can I have two complementary panels like this and show which one has the focus, in a way that's better than my (too subtle) border color?