So you got some interesting science fiction youneed to share or advertise, and John De Lancie and Leonard Nimoy are not exactly what you are looking for? Then you are in a need to search out some serious alienc voices talent...
How do alien voices sound? We really don't know, so we need to guess. But in this day and age when any connection with science fiction films, TV productions, books, comics, audio productions we often need to make that guess sound realistic. On one hand, it can be a dark foreboding aliens that want to take over our planet on the other, they could be friendly, wanting real contact and advancmenet of humanity. In either case, alien voices have their place.
Any audience weaned on science fiction in any shape and form will certainly expect that any fictional alien race is represented by a specific alien voice. Very often, connected to this audience is the one that is actively researching whther aliens really do exist and whether they have visited and/or are visiting earth. Any recreation of possible human//alien encounters requires an imaginative recreation of an alien voice or voices.
The tone and pitch of an alien voice can actually be as wide as imagination goes, from very high and even shrill, to very low, and ground shaking. Such voices in most cases speak in an imaginary tongue, like Klingon from "Star Trek", which has actually given an imaginative detailed development by the fans. When an alien voice is 'translated' into a human language like English, it is often given the sound like it is going through a computerized translation, sounding like artificial intelligence in early development.