What's the vocal effect for the Vogons in the Hitchhiker's Guide to the Galaxy radio series?
According to my book of the radio scripts the pre-Babel fish voice was done by ignoring his description of 'a combination gargling, howling, sniffing and fighting off a pack of wolves' and just revering the speech recording. I think they did a lot of stuff with just tape.
It doesn't specify what was used for the translated Vogon voice, but they had access to an ARP Odyssey and an early vocoder. They had to put various actors in cupboards to separate their audio.
I tried to find detail on how they recorded the original, but no joy.
This chap has tried to emulate the sound effect as part of his University course - https://ccrma.stanford.edu/~aarun/220a/hw4.html
In his words: