interval signal, or tuning signal, is a characteristic sound or musical phrase used in international broadcasting, numbers stations, and by some domestic broadcasters, played before commencement or during breaks in transmission, but most commonly between programmes in different languages. It serves several purposes:
It assists a listener to tune his or her radio to the correct frequency of the station. This is because most older and cheaper radio receivers do not have digital frequency readout.
It informs other stations that the frequency is in use.
It serves as a station identifier even if the language used in the subsequent broadcast is not one the listener understands.
The practice began in Europe in the 1920s and 1930s and was carried over into
shortwave broadcasts. The use of interval signals has declined with the advent of digital tuning systems, but has not vanished. Interval signals were not required on commercial channels in the United States, where jingles were used as identification.
Broadcasting services and interval signals
BBC World Service: (English programme), Bow Bells Lillibullero, three notes tuned B-B-C (non-English programme, non-Europe), four notes tuned B-B-B-E (non-English programme, to Europe).
Radiodifusión Argentina al Exterior: First eight notes of by Carlos Gardel, followed by people saying the station's name in eight languages. Mi Buenos Aires querido
Ö1: Three notes tuned O-R-F by Werner Pirchner, played on  viola.
Radio Belarusi ? ( Radzima maja darahaja ,"My dear Motherland") by Uladzymyr Andranika? and Alesia Ba?yla.
China National Radio, China Radio International: Chime version of (" March of the Volunteers").
Voice of the Strait News Radio: Bell version of (" Three Rules of Discipline and Eight Points for Attention")
Radio Habana Cuba: Melody of La Marcha del 26 de Julio ("March of the 26th of July") by Agustín Díaz Cartaya
DR P1: , played on xylophone. Drømte mig en drøm i nat 
Radio France Internationale: Electronic-disco, culminating in the last 8 measures of . La Marseillaise
Deutsche Welle: Celesta version of Es sucht der Bruder seine Brüder from Fidelio by Ludwig van Beethoven.
Voice of Greece: The Tsopanakos (Little Shepherd), played on floghera. 
All India Radio: A tune composed by Walter Kaufmann or Thakur Balwant Singh, used since 1936. 
Radio Republik Indonesia: ("Solace on Coconut Island"), composed by Rayuan Pulau Kelapa Ismail Marzuki.
Radio Japan: Kazoe-uta (Japanese counting song) ("Sakura Sakura" - Cherry Blossoms) .
Voice of Korea: Melody of (" Song of General Kim Il-sung").
Pyongyang FM - Melody of (" Song of General Kim Jong-il")
KBS World Radio: Dawn.
RTL Radio: Feierwon by Michel Lentz, played on chimes. 
Voice of Mongolia? ? ("Motherland").
Radio New Zealand International: The call of a New Zealand bellbird.
Far East Broadcasting Company: Lord Jesus to Save Sinners.
Radio Veritas Asia: O via, vita, veritas
RTÉ Radio 1: Chime version of O'Donnell Abú ("O'Donnell Forever"). 
Radio Romania International: Pui de lei by Ionel G. Br?tianu
Radio Sakha: Excerpt from a Yakut folk song.
Radio Slovenia: Electronically generated cuckoo chirping.
Radio Ukraine International ? ( The roaring and groaning Dnipro is wide).
WEWN, later EWTN Global Radio: Salve Regina
National Broadcasting Company: 3 chime-like notes.
Trans World Radio: . What a Friend We Have in Jesus
Voice of America: Brass band version of . Yankee Doodle
Vatican Radio: , played on celesta. Christus Vincit Radio Nacional de Venezuela - Canal Internacional: Beginning of Alma Llanera by Pedro Elías Gutiérrez and Rafael Bolívar.
Cyprus Broadcasting Corporation: Avkoritsa by Andreas Mappouras, played on guitar
Radio Prague: Trumpet version of Kup?edu levá ("Forward, Left") by Jan Seidl Adagio - Allegro molto from Symphony No. 9 by Dvo?ák.
Radio Finland: Pim-pam-pulla by A. O. Väisänen. 
Radio France Internationale: Trumpet version of a popular song Nous n'irons plus au bois. 
Berliner Rundfunk: Motif from the opera by Regina Albert Lortzing, played by trumpets.
Radio Berlin International: Beginning of ("Risen from Ruins"), played on chimes. Auferstanden aus Ruinen
Radio DDR: First few bars of Wann wir schreiten Seit' an Seit'.
Deutschlandfunk: Celesta version of Dir, Land voll Lieb' und Leben from "Ich hab mich ergeben" by Hans Ferdinand Maßmann. 
Radio Budapest: Excerpts from the suite 1848 by T.K. Polgar played on 3 trumpets and 2 cornets.
Kol Yisrael: Trumpet and drum version of . Hatikvah
Rai Italia Radio: Mechanically generated canary chirping.
Trans World Radio: Hymne Monégasque
NPO: First seven notes of , played on clarinet ( Wilhelmus Radio 1 and Radio 5), synthesizer ( Radio 3), spinet ( Radio 4) and carillon ( Radio 2). 
NRK P1: Motif from Sigurd Josarfal by Edward Grieg. 
Radio Norway International (former international service of NRK): Ancient folk tune from the Hallingdal region and 
Radio Katowice: Sound of a hammer striking an anvil. 
Radio Olsztyn: Excerpt from O Warmio moja mi?a by Feliks Nowowiejski, played on calliope.
Polish Radio External Service: Excerpt from Przniczka by Stanis?aw Moniuszko, played on piano. 
Radio Polonia: Piano version of Etude No. 12 ("Revolutionary Etude") by Frédéric Chopin.
Radio Sweden: Chime version of Ut i vida världen ("Out in the Wide World"), composed by Ralph Lundsten and the opening notes of Carl Michael Bellman's Storm och böljor tystna r'en. .  
Radio Bucharest 1 and Radio Bucharest External Service (pre-1989): Fragment from Cantata anilor lumin? by Anatol Vieru
Radio Canada International: First four notes of , played on piano or O Canada autoharp.
Radio Mayak: Vibraphone version of Moscow Nights.
Voice of Russia: "Majestic" chorus from the "Great Gate of Kiev" portion of by Pictures at an Exhibition Mussorgsky.
Radio Serbia: . Bo?e pravde
Radio Slovakia International: Kto za pravdu horí.
Radio RSA (former international service of Apartheid-era South African Broadcasting Corporation): Bokmakierie chirping and first bars of Ver in die Wereld, Kittie, played on guitar.  
Radio Beromünster: D' Zit isch do, played on music box.
Swiss Radio International: Lueget, vo Berg und Tal.
Voice of Turkey: Makam, played on piano.
Radio Moscow (former international service of the Soviet Union): ? (" Wide Is My Motherland") Midnight in Moscow, played by balalaika.
WYFR: First two bars of To God Be the Glory by William Howard Doane played by brass band
Radio Yugoslavia (1980-1989): First bar of Dru?e Tito,ljubi?ice bjela anonymous Partisan song, in various orchestral renditions 
Radio Yugoslavia, later International Radio of Serbia and Montenegro: Jugoslavijo by Nikola Hercigonja. NWDR: The 4th symphony by Brahms.
Classical Radio Station
WQXR-FM in New York City, during its ownership by The New York Times Company, played different variations of a classical infused gong with the ID read at the same time as "The Classical Station of the New York Times, WQXR, New York (And WQXR.com 2000-2009)
Numbers stations interval signals
Numbers stations are often named after their interval signals, such as The Lincolnshire Poacher or Magnetic Fields after "Magnetic Fields Part 1" by Jean-Michel Jarre.
References Frost, Jens Mathiesen (1974). World Radio-TV Handbook 1974. London: Billboard Publications. p. 408. ISBN . 0823058980 Sennitt, Andrew G.; David Bobbitt (December 2005). World Radio and Television Handbook 2006. Billboard Books. p. 608. ISBN . 0-8230-7798-5
Sennitt, Andrew G. World Radio and Television Handbook 1997. Billboard Books. p. 560. ISBN . 0-8230-7797-7