The audio files that you can download from this page accompany the article 'SPL De‑esser Collection', which appeared in SOS June 2012
This is a very typical de‑esser application. The original material does not sound bad at all, but it is too bright and there are some strong consonants which need to be tamed. In this example the SPL de‑esser gets the sibilance under control without any obvious side‑effects.
Even though they are designed specifically for vocals, a de‑esser can be a very helpful tool in a fairly huge range of possible applications. The more you think about it, the more use cases come to mind. In this case, the SPL de‑esser smoothens a overly aggressive drum machine, taking away a good portion of the sharp and harsh transients of the individual drum events. You can take this approach even further for some creative loop design in the style of early Portishead productions.
This is a typical application for M/S de‑essing. Imagine you are mixing or mastering a production, and you do not have access to all the individual tracks, but only to some stereo stems. In this case, lead and backing vocals have been grouped on a single stereo bus. The main vocal sounds great, but the backings are much too bright. Luckily, the lead vocal track is in the centre, whereas the harmonies have been panned left and right. A de‑esser that affects only the Sides portion of the signal can reduce the sibilance in the harmonies while leaving the main vocal untouched.