Fix Sharp S and T Sounds

When letters like S and T come out as a high-pitched hiss (caused by air pushing against your teeth), that's called sibilance. It's incredibly annoying, and I struggled with it for a long time, trying stuff like EQ sweeping, before I realized Final Cut has a free, built-in tool that handles it accurately and easily: the DeEsser.

Detector and Suppressor

With your clip selected, drag DeEsser from your effects tab onto it. Unlike the compressor, there aren't many knobs here. There are two sides: the Detector finds the sharp S and T sounds based on the frequency you choose, and the Suppressor decides which frequencies get turned down and by how much. Sibilance sits in different frequencies depending on the person, generally somewhere from 5,000 to 10,000 Hz, so you'll play your audio while you dial it in.

Dial in the detector

Down at the bottom there's a Monitor tab that lets you isolate the detector, sensitivity, and suppressor. Click the detector monitor and play your audio (heads up, it'll sound pretty quiet), then swing the frequency knob to find where those S sounds come through strongest. Flip to sensitivity, and the more you raise it, the more of that detected sound gets passed through to be suppressed. With the monitor up you can actually hear exactly what will be suppressed, so if you swing to a range with no sibilance, you'll notice it right away. A good starting point for sensitivity is about halfway, but it depends on the voice. There's also a smoothing control: no smoothing makes the suppression pop in and out harshly, while too much starts grabbing the rest of your words, so find a middle ground.

Set the suppressor

Finally, the Suppressor controls which frequencies get suppressed and how much. What I do is use the suppressor monitor to bring up the strength and find the frequency, then switch the monitor off to hear how it sounds overall. As far as I know, you'll want the suppressor frequency in a similar range as your detector frequency. Increase the strength and adjust the frequency as you play the audio, and you'll see the activity LED light up orange whenever suppression kicks in. Do it right and you go from harsh, hissy S sounds to smooth, clean audio.