Bloodnok:(voiced by Peter Sellers) Mind your language! There may be sensitive Scots Guardsmen present! Flowerdew:(voiced by Peter Sellers) It's all right, I don't mind really, honestly, it's quite all right. Bloodnok: Sellers! How dare you change your voice from mine into his for one joke only!
Another example from the Goon Show episode 'The Histories of Pliny the Elder'.
Moriarty: Why don't you stop him Julius Caesar? (Ceasar uses Grytpype's voice, played by Sellers) Bloodnok: How can I when I'm playing the part of Bloodnok? ** Spike Milligan was absent for one episode and Sellers performed his parts as well! (His Eccles in particular was flawless.) But just wait until you hear Sellers' albums...
Yet another example from the episode 'The £1,000,000 Penny'.
Henry Crun:(Sellers) Now who was that knocking? Moriarty: It was my friend Grytpype-Thynne (also played by Sellers). Henry Crun: I can't see him. Moriarty: That's because you are playing him. Henry Crun: What? Moriarty: He's never here when you're here. Henry Crun: I don't understand. Moriarty: Neither do the audience, that's why it isn't getting a laugh!
Becomes even more amazing when you realise that most of the roles were done by the three main cast members and Harry Secombe only played one of them (main character Neddie) most of the time. Sellers was doing well over 90% of the one-off characters.
Former Goon Michael Bentine also did a radio sketch show where he performed all the voices, but that was done by editing. The Goons did it live on stage.
This trope has been known to occur quite a bit, especially when farmer Tom Riley and shady businessman Bart Rathbone were running against each other for mayor. Ed Walker, who played both, switched voices in real time, meaning he was literally debating with himself.
This also happens when Dr. Regis Blackgaard runs his brother Edwin out of town.
...and whenever Eugene Meltsner converses with Harlowe Doyle, P.I.
When Kevin Clash (Elmo's puppeteer and voice) was on Wait Wait Don't Tell Me, he managed to interrupt himself with Elmo's voice. It really creeped the host out, especially when it sounded like they were speaking at almost the same time.
The Phil Hendrie Show: All the guests on his spoof talk radio show.
In the entirely improvised sitcom The Masterson Inheritance, each performer would inevitably end up playing several different roles, most of them made up on the spot and many with ridiculous voices. Naturally, they often ended up talking to each other. Paul Merton ended up doing this pretty much ever episode (especially when the others deliberately arranged things so he'd have to). He'd sometimes wriggle out of it by having one character tell the other(s) to shut up while he spoke, or just have whichever one had the most annoying accent drop dead from a heart attack.
Mrs MacAllister: How can you stand here and say that to me? Mrs Naughtie: It isn't easy.
In another episode, the Laird (played by Jeremy Hardy) had an argument with his mother (played by Jeremy Hardy with a silly high-pitched voice) which ended "Now take me home before anyone realises you're doing both voices". Not being a show to let a joke rest, the Laird's mother later had a party with Mrs Dougal, Mrs Hamish, and Grandpa Naughtie.
Spoofed repeatedly on BBC comedy The Burkiss Way, which on several occasions features conversations between characters with exactly the same voice. Usually lampshaded in the most blatant way possible, and without the performer even pausing between lines.
"Over to Professor Norman Stillmetalking. Hello!" "Now, a man whose voice isn't done by me. Good evening. Except on special occasions."
In one episode, Jo Kendall uses the same voice for two different characters, simply by introducing every other sentence with "in a different voice".
In one spectacular example, John Cleese is required to have one of his characters eaten by another. There are almost twenty seconds of discussion whether it's physically possible, before he is told to get on with it.
John: I don't come here and grace you with my acting skills to be eaten. Anyway, if there's animal eating to be done, I want to do it. David: You did do it.... You ate yourself. John: Well, that's even worse. That's auto-cannibalism. Makes you deaf.
In another episode, Tim Brooke-Taylor, playing Tim Brown-Windsor, Lady Constance and Lady Constance's sister Flossie, genuinely gets mixed up when the three of them have to share a scene. Naturally, they Throw It In.
In yet another episode, two of Graeme Garden's characters have an argument together. The scene is introduced by John Cleese explaining that it isn't going to be very funny, but Graeme would like a round of applause anyway to imply to the home audience that it's very difficult, even though (according to Cleese) it isn't.
And in the end of that season, Graeme takes over the serial — and is, at that point, playing the main hero (Professor Prune), the main villain (Fetish), and the narrator. Naturally, chaos ensues.
Fetish: So, professor, We Meet Again! Professor: Oh, you monster! But I'm not beaten yet! Fetish: Oh no? Professor: No! Fetish: Oh! Professor: You see— you see— Fetish: Go on! Professor: I will! Fetish: Please do!
The Walton & Johnson show has, alongside John Walton and Steve Johnson, three characters voiced by Johnson: Billy Ed Hatfield, a redneck Army veteran, Mister Kenneth, a gay hairdresser, and Mr. Eaux, a militant black nationalist from New Orleans. Needless to say, all three characters frequently get into fights with one another and with callers.
Ever since Katy Manning started playing Paul Magrs's dotty Time Lady Iris Wildthyme for Big Finish, it was inevitable that eventually there'd be a story where Iris met Jo Grant. It happens in the Companion Chronicles audio Find And Replace. Manning recorded all their conversations in one take, rather than recording each voice separately.
The Tenth Doctor audio story "Dead Air" is presented as a story recorded by the Doctor onto tape during downtime while fighting a sound-manipulation creature, in which he does the voices of all of the other people in the story with a variety of accents. However, towards the end of the story, events 'catch up' with him and we hear him conversing with the monster, who takes speaks with both the actual voice of the one-shot companion Layla (who sounds exactly like Tennant in a Scouse falsetto) and, when the Doctor tells it not to use her voice, the Doctor's own voice. It's kept from being confusing by the tape artefact effects applied to the sound creature's voice whenever it speaks, and by the fact that the sound creature uses a neutral Southern English accent when using the Doctor's voice instead of the usual Cockney.
The gimmick of the Companion Chronicles is that the companion actor plays both their usual character providing in-story dialogue and narration, and their Doctor, imitating their voice as best as they can. In-story dialogue is treated with effects to make it sound diegetic. Many have extra actors performing side character roles (or at least the monsters), but some are entirely just a companion and a 'Doctor' talking to him or herself.
Used along with Tomato in the Mirror to pantswetting effect in "The Holy Terror", where a Goo Goo GodlikeHumanoid Abomination speaks in a slightly unnatural-sounding child voice. When the Doctor corners it and asks it to "speak in a deeper voice like adults do", its voice slowly ages up from a child to a teenager to an older man... to the same voice as the old scribe helping the Doctor out.
In the Haruhi SuzumiyaSound Around radio drama a musical monster causes Kyon, Itsuki, Yuki and Mikuru to lose their voices and speak with Haruhi's voice instead. Thus we have Aya Hirano talking to herself as four different characters (although with Mikuru it is almost impossible to tell the difference). It gets even more confusing when Itsuki does an impression of Haruhi.
As a ventriloquist, Edgar Bergen naturally did this a lot on The Chase and Sanborn Hour.
Often happened to Bob & Ray, as a consequence of playing both hosts and (often multiple) guests on their various shows, assisted by their uncanny timing and familiarity with each other. The effect is most spectacular when baritone Ray and his falsetto character Mary McGoon hold rapid-fire discussions — often with Ray's other character Webley Webster chiming in — with Bob and two or more of his characters.
Since Chet Lauck and Norris Goff of Lum And Abner played virtually all of the characters of the show, this happened quite frequently. There are episodes where one of the actors would be on vacation, and the entire show consisted of the other actor basically carrying on a conversation with himself.
One That Mitchell and Webb Sound sketch features a radio debate on the death penalty between two men both played by Robert Webb, who sound exactly the same. It degenerates into chaos as the moderator, played by David Mitchell, desperately tries to find a way to tell the two men apart. At the very end, Webb starts playing the moderator as well.
On the sketch show Hello Cheeky, there were four actors, one of whom generally only played one role. They mostly managed to avoid talking to themselves, except for a few sequences in which Tim Brooke-Taylor plays a woman and a man in the same scene, at one point even muttering "You do feel a fool talking to yourself..."
In one episode, a sketch is completely derailed as the cast change their roles around in an attempt to avoid talking to themselves.
John: I am Lieutenant Jeffrey Snob, and I don't know what I'm doing here. And don't bother trying to tell me, foreign milkman, because I'm playing that part as well. Barry: Don't worry. I will take over the part of Klaus while you play that part. Tim: Isn't it confusing enough as it is? Let me explain...John was playing Klaus, so Barry took over the role of Klaus so Klaus could talk to Mungo...no, wait, Barry's playing Mungo...er, when Mungo became Jeffrey, John started playing Jeffrey but he's also playing Klaus...
Done literally by Brian Phelps of the Mark & Brian Radio Program. One sketch one the show had him portraying George W. Bush and Governor Arnold Schwarzenegger speaking to one another. Brian also challenges his co-host Mark to try and trip him up at the end of the sketch, which he does by rapid firing questions to Arnold and then Bush.