Descript's low-pass filter — also known as a "hi-cut" filter — allows you to trim out high-frequency audio from your media clips. This can be useful in situations where electromagnetic interference (say, from a cellphone close to your microphone) may have gotten onto a recording. The effect comes with several presets to choose from, so you can try out different settings to get the desired result you're looking for. You can apply the effect from the Audio Effects section of the Properties Panel.
|set the frequency where you want the roll-off to begin.