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subaudible tone wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 overview 2 use for filmstrips 3 external links toggle the table of contents subaudible tone add languages add links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia in band signaling for broadcast radio automation this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources subaudible tone news newspapers books scholar jstor july 2007 learn how and when to remove this message for the use of subaudible tones in two way radio see ctcss a subaudible tone is a tone that is used to trigger an automated event at a radio station a subaudible tone is within the audible frequency range however it is usually at a low level that is not noticeable to the average listener at normal volumes it is a form of in band signaling overview edit these tones are included in the audible main portion of audio in the case of a satellite on tape these often are filtered typically subaudible tones are at one of the frequencies 25 35 50 75 hertz hz or combinations of those frequencies until computerized radio automation became inexpensive and common 25 and 35 hz were used either in the audio stream or in the case of tape cartridges used in radio broadcasting better known as carts on a special track on the tape to indicate to a radio station s automation system that it was time to trigger another event with the advent of computers and digital satellites these tones are relegated to triggering commercial announcements and legal ids on a dwindling number of radio networks external data channels have supplanted tones in the audio sent independent of audio on digital satellite feeds for radio these trigger relay closure terminals on the satellite receiver starguide is a prominent system use for filmstrips edit later filmstrip projectors used subaudible tones to advance to the next frame in a filmstrip presentation previously the phonographic record or audio cassette accompanying a filmstrip to provide its soundtrack would have an audible tone to signal the person operating the projector to advance the film to the next frame however automatic filmstrip projectors were introduced in the 1970s that had an integrated phonograph or cassette player that would read a subaudible tone of 50 hz recorded on the soundtrack to trigger the projector to advance to the next frame automatically most cassettes accompanying filmstrips from the 1970s and 80s have one side of the media with audible tones for use with manual projectors and the other side with the same program audio but with 50 hz subaudible tones instead for automatic projectors some filmstrip releases combine audible and subaudible tones making the filmstrip and its companion cassette or record compatible with any filmstrip projector external links edit examples of subaudible tone units this broadcasting related article is a stub you can help wikipedia by adding missing information v t e retrieved from https en wikipedia org w index php title subaudible_tone oldid 1351296847 categories radio technology broadcast engineering broadcasting stubs hidden categories articles with short description short description matches wikidata articles needing additional references from july 2007 all articles needing additional references all stub articles this page was last edited on 27 april 2026 at 03 30 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents subaudible tone add languages add topic