The Lombard effect is the involuntary tendency of a speaker to increase the intensity of the voice when speaking in loud noise to enhance audibility. This change includes not only loudness but also other acoustic features such as pitch, rate and duration of sound syllables.
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 surrounding as in after-concert parties.
Noise has been found to effect the vocalizations of animals that vocalize against a background of human noise pollution. Birds sing with a higher frequency than those in quieter area to overcome the masking effect of the low frequency background noise pollution of cities. Beluga whales in the St. Lawrence River estuary adjust their whale song so it can be heard against shipping barge noise.
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