Warren Huart demonstrates serial compression on vocals, stacking a second compressor in series to push the vocal further forward in the mix. Rather than loading more work onto a single compressor, the idea is to let the first unit handle general leveling while the second one, set to a high ratio around 20:1, catches the remaining peaks and adds presence.
Warren starts with the threshold pulled high and gradually brings it down until the compressor just grabs the peaks. The result is a more even, upfront vocal that doesn't sound over-compressed. A clear bypass comparison makes the effect easy to hear.