Radio Voice

Whenever we hear someone talking through a radio (or any sort of communications device) their voices are always, always slightly distorted so that the audience can tell that the voice is being received through the communications link (as opposed to being spoken by someone who is slightly off-camera). This occurs even on shows where the builders of the communications devices in question achieved faster-than-light space travel hundreds of years ago and who by all rights ought to have come up with a perfect-fidelity microphone/speaker system long ago.

The effect can be accomplished by running the audio through a bandpass filter to remove all frequencies outside a specified range. For example, the U.S. telephone network uses a filter that keeps only frequencies between roughly 300 to 3500 Hz. It's symbolized in comic books by adding a jaggey or "lightning bolt" effect to some part of a speech bubble.

Variant: Voice communication over any kind of magical or psychic link (e.g. telepathy) will have a different effect, making the voice sound spooky or echoey instead of metallic, but the trope is the same.

This may be simply to serve the Rule of Perception, because otherwise we might get confused as to who's where. It also has a good technical reason: transmitting only 3 kHz worth of audio is far easier than transmitting 20 kHz regardless of what transmission medium or method is being used, and it's OK to do this when the only thing that matters is the speech itself and not so much the audio quality. This may also be explainable in-Verse as a user interface feature; the fictional designers of the fictional system may have felt it was useful to be able to distinguish radio voices from the voices of people present in the room.

Goes well with Walkie-Talkie Static. See Also: The Coconut Effect.

Anime & Manga

 * The in-head cyber-telepathy used in all Ghost in the Shell media (except manga, obviously) recycles a distinctive filter set from The Movie. It's basically just a spatializer, designed to make the sound seem far away, in a way different from a standard reverb or echo.
 * Used in Prétear for all of the scenes that allow us to listen to Sasame's "Words Gate" radio show. Particularly notable is when Mawata is listening to a recording of his show, only for her player to run out of batteries as Sasame's voice comes in loud and clear to repeat what he said on the show--in person.

Film

 * The voice of Korben Dallas' Taxi in The Fifth Element sounds like a late 90s speech synthesizer. And radio/television communications are hardly better (though you wouldn't be able to tell with Ruby Rhod anyway).
 * Used in the Star Wars movies, in particular the first movie with the attack on the Death Star, where the distortion was heavy filtered through what sounded like a single sideband transmitter. The Star Wars Expanded Universe noted that this was deliberate on the part of the Rebellion, as it helped disguise who was talking (being rebels, it was rather useful for their identities to remain unknown to the Empire). And while they say very little, the Imperial pilots' voices are significantly less distorted.
 * And any time a stormtrooper talks, his or her voice is flattened and made to sound a little more artificial. It's supposedly the speaker in the helmet. Droids, too.
 * Truth in Television if you use a voicemitter mounted on a gas mask. The first time you wear one, it can be very difficult not to talk about missing droids or transferring prisoners to holding cells.
 * The Rebellion's reasons extended past just disguising the voice into security concerns, putting more effort into encryption than fidelity (and one would assume that keeping transmissions short would help keep enemy sensors from getting too accurate a fix).
 * Particularly bad in the Mystery Science Theater 3000 featured movie Monster a Go-Go!, prompting Crow to riff "take the kazoo out of your mouth!" and "They're talking to Charlie Brown's mom!".
 * Played straight in The King's Speech, Truth in Television for its day.
 * THX 1138.
 * Parodied in High Anxiety, when Mel Brooks asks his secretary to repeat her intercom message without holding her nose. She replies in a perfectly normal voice.
 * Mel Books also parodied this trope in Spaceballs; specifically, the "jammed radar" scene featuring Michael Winslow as the Spaceball manning the radar station.

Live Action TV

 * Star Trek, all series. Beam living people from one place to another? Check! Perfect the fully immersive, utterly realistic holodeck? Check? Build a communicator that can transmit sound with better quality than an FM radio? Still on the to-do list.
 * The new Battlestar Galactica may be an instance in which this trope is justified; except for having artificial gravity and the jump drive (which is, admittedly, a big "except"), their tech isn't any more advanced than real life, and this troper at least can hear the distortion on, e.g., her cell phone.
 * The old BSG (iirc) and Star Wars' Rebel Alliance fighters (definitely) had the same effect for their military radio comms. It's a close simulation of the actual sound of single sideband radio, as still used by ham operators today, and military voice comms a few decades ago. Besides the "telephone filter" there is a slight, and changing, pitch shift. Note too that the new BSG calls it "wireless," not "radio," and that their "civilian" radio does not have the SSB effect. Speaking of new BSG tech, while they have computers (with image enhancement software) they don't seem to have television. Hm, maybe the latter explains how they had time to invent jump drives and artificial gravity!
 * Hmm. It seems that in Caprica's time, when they invented the Cylons, they did have television. "'Curiouser and curiouser,' said Alice."
 * Television was present on the twelve colonies (Baltar did an interview just before the original attack). Its likely that after the attack and while on the run, there were just no adequate facilities for a TV production and/or there weren't a lot of TVs that were brought along anyway.
 * They did have televisions in the fleet. An entire episode is devoted to the making of a documentary about the Galactica's pilots. We just don't ever see people sitting around watching television, justified in that all of the characters in that show were routinely pretty busy.
 * Used in the Doctor Who episode "Silence in the Library"/"Forest of the Dead", when Charlotte watches what's going on on the TV. Particularly notable because the background music is similarly treated, suggesting her observation of the library comes with its own chase-scene music.
 * This may be justified since  and since it's a chase seen on the TV it should have chase music.

Music

 * Musical example; on Pink Floyd's Wish You Were Here album, the end of the song Have a Cigar is distorted to sound as though it's playing on the radio. This leads into a sequence where the radio is tuned through several channels rapidly before settling on the opening riff of the title track. Eventually, a second guitar joins in undistorted, symbolizing the listener (ex-frontman Syd Barret) playing his own guitar along with the radio.
 * Live they would sometimes have the main riff of Wish You Were Here played on an actual radio.
 * Honey Pie by The Beatles, for the single line "Now she's hit the big time!"
 * In the song "Patterns" by Simon and Garfunkel. After "The pattern never alters, until..", "The rat dies" is heard in Radio Voice.
 * Several of Doctor Steel's songs have epigraphs, some sampled from old Public Service Announcements such as "Duck and Cover", others deliberately done as a parody of such announcements.
 * In Starship's song We Built this city, about 2/3 of the way through, the song breaks for a radio-style announcement of an advert for a San Francisco radio station with a very much radio sounding voice.

Radio

 * Truth in Television - er, I mean Radio: Some BBC Radio productions achieve the effect of a radio voice by the simple yet obvious expedient of feeding the voice through an appropriately-sized loudspeaker.
 * In the radio version of The Shadow, the audio cue for "Lamont's turned invisible now" was the same filter used for "This character is talking over the telephone". Which somewhat limited the scriptwriters -- Lamont Cranston could get phone calls from other characters, but could only call other characters (and be heard over the line from their POV) as The Shadow.

Video Games

 * The Halo series. When Cortana is in her holographic form or in your helmet and talking to you, her voice is perfectly natural, but when she's speaking to someone else through your radio, her voice distorts--even though you're hearing her through the same set of speakers.
 * The marines in Half Life, as well as the Combine guards and soldiers in Half Life 2.
 * The Combine are speaking through a vocoder, sugically implanted as part of their conversion from human. The modulation is intentionally done. Marines still have no excuse.
 * In Mass Effect and especially its sequel, your character (Commander Shepard) and squad will walk around on an alien planet or city in full battle armor, with the player give the option to wear a helmet or show the character's face. In the second game, there is a subtle but noticeable filter between Shepard's normal voice, and how it sounds when s/he's talking with the helmet on (And depending on the type of helmet currently equiped, it might even show blinking lights at the mouthpiece which move in time to his/her voice).
 * And of course Tali's voice always has a slight buzz to it.
 * Space Marines in the Warhammer 40000: Dawn of War series.
 * Used subtly in the Modern Warfare games. Your team mates voices pick up the Radio Voice effect if they happen to be farther than a short distance from you when they are talking.

Web Animation

 * Virtually all communication in Red vs. Blue is conducted over radio, even when the characters speaking are standing in front of each other. Rooster Teeth tried to remove the effect at one point, but fans expected it there, so they put it back in.

Western Animation

 * Parodied in an episode of Invader Zim, where a policeman is driving down the road and hears an utterly unintelligible static-choked mumble from his radio. The policeman picks up the handset and talks into it in an equally meaningless Charlie Brown-esque mumble, revealing that it's not actually radio interference--in this world, cops just talk like that. Both sides can apparently understand each other perfectly.
 * Ben's various forms in the original Ben 10 series were typically voiced by different voice actors than human Ben. For the bulk of the series, the only exception was the technology-based alien form, Upgrade, who spoke with Ben's voice with the Radio Voice distortion effect.