The background sounds accompanying Orac and Zen’s speech from the show are readily available. (I’ve got an import CD that I traded VHS tapes of various shows for with a bloke in Scotland, and I’ll be damned if it isn’t one of the handiest CDs I’ve ever owned, featuring sound effects loops from Blake’s 7 and Hitchhiker’s Guide To The Galaxy. There’s a reason it has survived multiple CD collection flips/purges.) The rest is just putting the right amount of reverb on it.
I actually would’ve liked it had he repeated the footage with no foley or reverb – it’d be neat to hear how much of what we think of as Orac or Zen’s voices are the post-production, and how much was the man himself. I think Orac’s voice treatment is enhanced immeasurably by the “looped/sped-up swarm of angry bees” sound that, for some reason, someone at the BBC in 1978 decided would be a perfectly normal sound that a supercomputer would make. (If any of my computers ever makes anything approaching that noise, it’s a sign that it’s about to be a lot less super as soon as the fan fails.)