The Lombard effect or Lombard reflex is the involuntary tendency of speakers to increase their vocal effort when speaking in loud noise to enhance the audibility of their voice. This change includes not only loudness but also other acoustic features such as pitch, rate, and duration of syllables. This compensation effect results in an increase in the auditory signal-to-noise ratio of the speaker’s spoken words.
The effect links to the needs of effective communication, as there is a reduced effect when words are repeated or lists are read where communication intelligibility is not important. Since the effect is involuntary it is used as a means to detect malingering in those simulating hearing loss. Research on birds and monkeys find that the effect also occurs in the vocalizations of animals.
Listeners hear a speech recorded with background noise better than they hear a speech which has been recorded in quiet with masking noise applied afterwards. This is because changes between normal and Lombard speech include:
- increase in phonetic fundamental frequencies
- shift in energy from low frequency bands to middle or high bands
- increase in sound intensity
- increase in vowel duration
- spectral tilting
- shift in formant center frequencies for F1 (mainly) and F2
- the duration of content words are prolonged to a greater degree in noise than function words
- great lung volumes are used,
- it is accompanied by larger facial movements, though these do not aid as much as sound changes
These changes cannot be controlled by instructing a person to speak as they would in silence, though people can learn control with feedback.
The intelligibility of an individual's own vocalization can be adjusted with audio-vocal reflexes using their own hearing (private loop), or it can be adjusted indirectly in terms of how well listeners can hear the vocalization (public loop). Both processes are involved in the Lombard effect.
A speaker can regulate their vocalizations particularly its amplitude relative to background noise with reflexive auditory feedback. Such auditory feedback is known to maintain the production of vocalization since deafness affects the vocal acoustics of both humans and songbirds Changing the auditory feedback also changes vocalization in human speech or bird song. Neural circuits have been found in the brainstem that enable such reflex adjustment.
A speaker can regulate their vocalizations at higher cognitive level in terms of observing its consequences on their audience’s ability to hear it. In this auditory self-monitoring adjusts vocalizations in terms of learnt associations of what features of their vocalization, when made in noise, create effective and efficient communication. The Lombard effect has been found to be greatest upon those words that are important to the listener to understand a speaker suggesting such cognitive effects are important.
Both private and public loop processes exist in children. There is a development shift however from the Lombard effect being linked to acoustic self-monitoring in young children to the adjustment of vocalizations to aid its intelligibility for others in adults.
The Lombard effect depends upon audio-vocal neurons in the periolivary region of the superior olivary complex and the adjacent pontine reticular formation. It has been suggested that the Lombard effect might also involve the higher cortical areas that control these lower brainstem areas.
Choral singers experience reduced feedback due to the sound of other singers upon their own voice. This results in a tendency for people in choruses to sing at a louder level if it is not controlled by a conductor. Trained soloists can control this effect but it has been suggested that after a concert they might speak more loudly in noisy surroundings, such as after-concert parties.
Noise has been found to affect the vocalizations of animals that vocalize against a background of human noise pollution. Experimentally, the Lombard effect has also been found in the vocalization of:
- Canaries 
- Common marmosets
- Cottontop tamarins
- Japanese quail
- Rhesus macaques
- Squirrel monkey.
- Zebra finches
- Beluga Whales
- Pale spear-nosed bats
- Acoustic ecology
- Auditory masking
- Bird vocalization
- Human voice
- Intelligibility (communication)
- Noise health effects
- Noise pollution
- Occlusion effect
- Whale song
- Slabbekoorn H, Peet M (July 2003). "Ecology: Birds sing at a higher pitch in urban noise". Nature. 424 (6946): 267. doi:10.1038/424267a. PMID 12867967.
- Halfwerk, W; Slabbekoorn (2009). "A behavioural mechanism explaining noise-dependent pitch shift in urban birdsong". Animal Behaviour. 78 (6): 1301–1307. doi:10.1016/j.anbehav.2009.09.015.
- Nemeth E., E; Brumm H. (2010). "Birds and Anthropogenic Noise: Are Urban Songs Adaptive?". American Naturalist. 176 (4): 465–475. doi:10.1086/656275. PMID 20712517.
- Lane H, Tranel B (1971). "The Lombard sign and the role of hearing in speech". J Speech Hear Res. 14 (4): 677–709. doi:10.1044/jshr.1404.677.
- Junqua JC (January 1993). "The Lombard reflex and its role on human listeners and automatic speech recognizers". J. Acoust. Soc. Am. 93 (1): 510–24. doi:10.1121/1.405631. PMID 8423266.
- Summers WV, Pisoni DB, Bernacki RH, Pedlow RI, Stokes MA (September 1988). "Effects of noise on speech production: acoustic and perceptual analyses". J. Acoust. Soc. Am. 84 (3): 917–28. doi:10.1121/1.396660. PMC . PMID 3183209.
- Brumm H (June 2004). "Causes and consequences of song amplitude adjustment in a territorial bird: a case study in nightingales". An. Acad. Bras. Cienc. 76 (2): 289–95. doi:10.1590/s0001-37652004000200017. PMID 15258642.
- Lombard É (1911). "Le signe de l'élévation de la voix". Annales des Maladies de L'Oreille et du Larynx. XXXVII (2): 101–9.
- Patel R, Schell KW (February 2008). "The influence of linguistic content on the Lombard effect". J. Speech Lang. Hear. Res. 51 (1): 209–20. doi:10.1044/1092-4388(2008/016). PMID 18230867.
- Winkworth AL, Davis PJ (February 1997). "Speech breathing and the Lombard effect". J. Speech Lang. Hear. Res. 40 (1): 159–69. doi:10.1044/jslhr.4001.159. PMID 9113867.
- Vatikiotis-Bateson E, Chung V, Lutz K, Mirante N, Otten J, Tan J (2006). "Auditory, but perhaps not visual, processing of Lombard speech". J. Acoust. Soc. Am. 119 (5): 3444. doi:10.1121/1.4786950.
- Pick HL, Siegel GM, Fox PW, Garber SR, Kearney JK (February 1989). "Inhibiting the Lombard effect". J. Acoust. Soc. Am. 85 (2): 894–900. doi:10.1121/1.397561. PMID 2926004.
- Zeine L, Brandt JF (September 1988). "The Lombard effect on alaryngeal speech". J Commun Disord. 21 (5): 373–83. doi:10.1016/0021-9924(88)90022-6. PMID 3183082.
- Waldstein RS (November 1990). "Effects of postlingual deafness on speech production: implications for the role of auditory feedback". J. Acoust. Soc. Am. 88 (5): 2099–114. doi:10.1121/1.400107. PMID 2269726.
- Konishi M (August 1965). "Effects of deafening on song development in American robins and black-headed grosbeaks". Z Tierpsychol. 22 (5): 584–99. PMID 5879978.
- Siegel GM, Schork EJ, Pick HL, Garber SR (September 1982). "Parameters of auditory feedback". J Speech Hear Res. 25 (3): 473–5. doi:10.1044/jshr.2503.473. PMID 7176623.
- Leonardo A, Konishi M (June 1999). "Decrystallization of adult birdsong by perturbation of auditory feedback". Nature. 399 (6735): 466–70. doi:10.1038/20933. PMID 10365958.
- Hage SR, Jürgens U, Ehret G (June 2006). "Audio-vocal interaction in the pontine brainstem during self-initiated vocalization in the squirrel monkey". Eur. J. Neurosci. 23 (12): 3297–308. doi:10.1111/j.1460-9568.2006.04835.x. PMID 16820019.
- Amazi DK, Garber SR (December 1982). "The Lombard sign as a function of age and task". J Speech Hear Res. 25 (4): 581–5. doi:10.1044/jshr.2504.581. PMID 7162159.
- Jürgens U (January 2009). "The neural control of vocalization in mammals: a review". J Voice. 23 (1): 1–10. doi:10.1016/j.jvoice.2007.07.005. PMID 18207362.
- Tonkinson S (March 1994). "The Lombard effect in choral singing". J Voice. 8 (1): 24–9. doi:10.1016/S0892-1997(05)80316-9. PMID 8167784.
- Johnson CI, Pick HL, Garber SR, Siegel GM (June 1978). "Intensity of guitar playing as a function of auditory feedback". J. Acoust. Soc. Am. 63 (6): 1930. doi:10.1121/1.381900. PMID 681625.
- Brumm H., H; Slabbekoorn H. (2005). "Acoustic communication in noise". In: Advances in the Study of Behavior. Advances in the Study of Behavior. 35: 151–209. doi:10.1016/S0065-3454(05)35004-2. ISBN 978-0-12-004535-8.
- Hardman SI, Zollinger SA, Koselj K, Leitner S, Marshall RC, Brumm H (March 2017). "Lombard effect onset times reveal the speed of vocal plasticity in a songbird". J. Exp. Eiol. 220: 1065–71. doi:10.1242/jeb.148734. PMID 28096429.
- Nonaka S, Takahashi R, Enomoto K, Katada A, Unno T (December 1997). "Lombard reflex during PAG-induced vocalization in decerebrate cats". Neurosci. Res. 29 (4): 283–9. doi:10.1016/S0168-0102(97)00097-7. PMID 9527619.
- Brumm H, Schmidt R, Schrader L (2009). "Noise-dependent vocal plasticity in domestic fowl". Animal Behaviour. 78 (3): 741–6. doi:10.1016/j.anbehav.2009.07.004.
- Brumm H, Voss K, Köllmer I, Todt D (January 2004). "Acoustic communication in noise: regulation of call characteristics in a New World monkey". J. Exp. Biol. 207 (Pt 3): 443–8. doi:10.1242/jeb.00768. PMID 14691092.
- Egnor SE, Hauser MD (December 2006). "Noise-induced vocal modulation in cotton-top tamarins (Saguinus oedipus)". Am. J. Primatol. 68 (12): 1183–90. doi:10.1002/ajp.20317. PMID 17096420.
- Potash LM (1972). "Noise-induced changes in calls of the Japanese quail". Psychonomic Science. 26: 252–4. doi:10.3758/bf03328608.
- Cynx J, Lewis R, Tavel B, Tse H (July 1998). "Amplitude regulation of vocalizations in noise by a songbird, Taeniopygia guttata". Anim Behav. 56 (1): 107–13. doi:10.1006/anbe.1998.0746. PMID 9710467.
- Scheifele P, Andrew S, Cooper RA, Darre M, Musiek FE, Max L (November 2004). "Indication of a Lombard vocal response in the St. Lawrence River beluga". In: Journal of the Acoustical Society of America. 117: 1486–1492. doi:10.1121/1.1835508. PMID 15807036.
- Luo, Jinhong; Goerlit, Holger R.; Brumm, Henrik; Wiegrebe, Lutz (22 December 2015). "Linking the sender to the receiver: vocal adjustments by bats to maintain signal detection in noise" (PDF). Scientific Reports. doi:10.1038/srep18556. Retrieved October 17, 2017.