Analysis, spectrum

Is it possible to reduce frequency zone in spectrum i.e. amplitude vs frequancy. For exemple, reduce to 8000Hz?

Analyze > Plot Spectrum will always expand to display everything it thinks in in your show – or your selection.

You can restrict the show by applying filters.

Effects > Low Pass Filter > 8000

That will make a new show that gracefully dies around 8000 Hz. If you analyze the new show, the display should show significant dip or rolloff around there. It will not do a “brick wall” drop. You can force tools to do that, but the music may be damaged.