Final Cut Pro

I need to split the clip.

Select a synchronized clip →Split with ⌘B

how do I do that without messing with the rest of the clip?

What exactly do you mean by “without messing with the rest of the clip”?

Don't want to change the length of your clip? Don't want to change the applied effects? Don't want to change the volume? Please clarify what you want to do.

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I have prepared a 10 second synced clip. Please explain using this diagram. Example: I want to split a synced clip at the part where B and C connect. I want to keep A to B as they are, but shorten the length of C to E by half (3 seconds).

A Sync Clip is a "clip type" or container. You'll see it listed in the Browser. Drop it into a Project Timeline and cut it up as you would any clip. It will not change what's inside of the Sync Clip container.