After updating to FCPX 10.3.4, I can no longer make any audio enhancements, such as reduce bass, or voice clarity etc. The "effects" box under audio tab is now uncheckable. What's up? I have really needed this the last couple of days.
The Effects box will not be selectable unless there is an audio effect applied to the clip in the timeline. Drag an EQ effect or something onto your clip to test and you'll see that then the effects parameter in the inspector becomes active and can be turned on or off.
You have the audio file selected. Select the channel you want to effect, or command-click to select the four channels. The enhancements are abled on a channel by channel basis. You can then click show opposite enhancements for loudness and such.