 Voice @-@ recording sessions were supervised by Pattillo and the Andersons , with Sylvia Anderson in charge of casting . <unk> was recorded once per month at a rate of two scripts per session . Supporting parts were not pre @-@ assigned , but negotiated by the cast among themselves . Two recordings would be made at each session : one to be converted into electronic pulses for the puppet filming , the other to be added to the soundtrack during post @-@ production . The tapes were edited at Gate Recording Theatre in Birmingham . 
