question: How is it that during the night every activity we make appears to be louder than during the day?
comment: During the day, there's a lot of background noises. Birds, traffic, people, televisions, etc. But we mostly tend to tune it out as it's unimportant. During the night, most of these noises are missing, so any noise sounds louder.
passages: Section::::European guidelines.
  
  The European Union (EU) set up European guidelines in respect to noise pollution. For nighttime, it is advised to not exceed the 40 dB L threshold outside the residence. An interim threshold of 55 dB L is set as an upper bound, because above this limit, (sleeping) disorders are more prevalent. However, about 20% of people living in or near urban areas suffer from sounds at night that exceed even the interim threshold.
  
  Section::::Law in the Netherlands.
   Urban areas typically exhibit diurnal noise patterns where background noise is higher during the daytime and lower at night and the noise floor directly correlates to urban activity (e.g., automobile traffic, airplane traffic, construction, and so on). A firearm’s muzzle blast may be masked by ambient noise during the daytime, but may be detected at greater distances during the quieter hours of darkness. A popular urban gunfire locator system typically uses six to ten audio sensors per square mile for trilateration. (two or three per square kilometer)
   Ambient noise is another variable that is conducive to distraction, yet it has been proven that a moderate level of noise actually heighten creativity. Professor Ravi Mehta conducted a study to research the degree of distraction induced by various noise levels and their effect on creativity. The series of experiments show that a moderate level of ambient noise (70 dB) produces just enough distraction to induce processing disfluency, which leads to abstract cognition. These higher construal levels caused by moderate levels of noise consequently enhance creativity.
  
  Section::::Affecting factors.:Walking.
   Later developmental effects occur as vasoconstriction in the mother reduces blood flow and therefore oxygen and nutrition to the fetus. Low birth weights and noise were also associated with lower levels of certain hormones in the mother. These hormones are thought to affect fetal growth and to be good indicators of protein production. The difference between the hormone levels of pregnant mothers in noisy versus quiet areas increased as birth approached.
   When a louder sound is heard, more hair cells are stimulated and the intensity of firing of axons in the cochlear nerve is increased. However, because the rate of firing also defines low pitch the brain has an alternate way of encoding for loudness of low frequency sounds. The number of hair cells that are stimulated is thought to communicate loudness in low pitch frequencies.
   Section::::Animals.:Bi-coordinate sound localization (owls).
  
  Most owls are nocturnal or crepuscular birds of prey. Because they hunt at night, they must rely on non-visual senses. Experiments by Roger Payne have shown that owls are sensitive to the sounds made by their prey, not the heat or the smell. In fact, the sound cues are both necessary and sufficient for localization of mice from a distant location where they are perched. For this to work, the owls must be able to accurately localize both the azimuth and the elevation of the sound source.
  
  Section::::History.
   Sleep increases the sensory threshold. In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events.
  
  During slow-wave sleep, humans secrete bursts of growth hormone. All sleep, even during the day, is associated with secretion of prolactin.
   Loudness is perceived as how "loud" or "soft" a sound is and relates to the totalled number of auditory nerve stimulations over short cyclic time periods, most likely over the duration of theta wave cycles. This means that at short durations, a very short sound can sound softer than a longer sound even though they are presented at the same intensity level. Past around 200 ms this is no longer the case and the duration of the sound no longer affects the apparent loudness of the sound. Figure 3 gives an impression of how loudness information is summed over a period of about 200 ms before being sent to the auditory cortex. Louder signals create a greater 'push' on the Basilar membrane and thus stimulate more nerves, creating a stronger loudness signal. A more complex signal also creates more nerve firings and so sounds louder (for the same wave amplitude) than a simpler sound, such as a sine wave.
   Section::::Noise studies.
   A 2-minute YouTube video addressing this issue by audio engineer Matt Mayfield has been referenced by "The Wall Street Journal" and the "Chicago Tribune". Pro Sound Web quoted Mayfield, "When there is no quiet, there can be no loud."
   Noise has been associated with important cardiovascular health problems, particularly hypertension. Noise levels of 50 dB(A) at night may also increase the risk of myocardial infarction by chronically elevating cortisol production.
  
  Roadway noise levels are sufficient to constrict arterial blood flow and lead to elevated blood pressure. Vasoconstriction can result from elevated adrenaline levels or through medical stress reactions.
  
  Section::::Psychological impacts of noise.
   The phon model can be extended with a time-varying transient model which accounts for "turn-on" (initial transient) and long-term listener fatigue effects. This time-varying behavior is the result of psychological and physiological audio processing. The equal-loudness contours on which the phon is based apply only to the perception of pure steady tones; tests using octave or third-octave bands of noise reveal a different set of curves, owing to the way in which the critical bands of our hearing integrate power over varying bandwidths and our brain sums the various critical bands.
  
  Section::::See also.
  
  BULLET::::- Sone
  
  BULLET::::- A-weighting
  
  BULLET::::- Decibel
   European robins living in urban environments are more likely to sing at night in places with high levels of noise pollution during the day, suggesting that they sing at night because it is quieter, and their message can propagate through the environment more clearly. The same study showed that daytime noise was a stronger predictor of nocturnal singing than night-time light pollution, to which the phenomenon often is attributed. Anthropogenic noise reduced the species richness of birds found in Neoptropical urban parks.
   The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound. The relationship between SPL and loudness of a single tone can be approximated by Stevens's power law in which SPL has an exponent of 0.67. More precise measurements, a model known as the "Inflected Exponential" function, indicate that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.
   When sensorineural hearing loss (damage to the cochlea or in the brain) is present, the perception of loudness is altered. Sounds at low levels (often perceived by those without hearing loss as relatively quiet) are no longer audible to the hearing impaired, but sounds at high levels often are perceived as having the same loudness as they would for an unimpaired listener. This phenomenon can be explained by two theories, called "loudness recruitment" and "softness imperception".
   The use of auditory stimulation has been shown to increase PGO waves during waking and sleeping cycles with neurons associated with transfers of auditory information. Even while the subject is awake and in total darkness, the amplitude of PGO waves increases by auditory stimulation. Another study also found that auditory stimulation increased the amplitude of PGO waves in slow-wave sleep and REM sleep and did not reduce the amplitude of the waves with repeated auditory stimulation. From this research, scientists can theorize that PGO wave generation from auditory stimulation contains a positive-feedback mechanism that can be excited by evoked PGO waves.
   The earliest mammals were generally small animals, probably nocturnal insectivores. This suggests a plausible evolutionary mechanism driving the change; for with these small bones in the middle ear, a mammal has extended its range of hearing for higher-pitched sounds which would improve the detection of insects in the dark. Natural selection would account for the success of this feature. There is still one more connection with another part of biology: genetics suggests a mechanism for this transition, the kind of major change of function seen elsewhere in the world of life being studied by evolutionary developmental biology.
   In his dissent, Marshall agreed with the majority that the government has a substantial interest in controlling noise but believed that it may not advance that interest by actually asserting control over the amplification equipment and thus over private expression itself. The government has an obligation to adopt the least intrusive restriction necessary to achieve its goals such as enforcing the noise ordinance that has already been adopted.
   Holter also used open-air recordings throughout the album. The track "Horns Surrounding Me" opens with "The noise of a running, panting man", which was caught using an open-air microphone. It was recorded by Holter while playing a game of tag with a friend, on a building where she lived in Echo Park.
  
  Section::::Critical reception.
   Section::::Perception of sound.:Loudness.
   Although lightning has a broad-spectrum emission, its noise power increases with decreasing frequency. Therefore, at very low frequency and low frequency, atmospheric noise often dominates, while at high frequency, man-made noise dominates in urban areas.
  
  Section::::Survey.
   Section::::Concert halls.
  
  Very large rooms like concert halls or large television studios have fundamental resonances which are much lower in frequency than small rooms. This means the closely spaced harmonic resonances are likely to lie in the low frequency region and thus the response tends to be more uniform.
  
  Section::::See also.
  
  BULLET::::- Loudspeaker measurement
  
  Section::::External links.
  
  BULLET::::- A simulation of the buildup of axial room modes (needs WebGL)
  
  BULLET::::- HTML5 Mode Calculator (3D view of each mode, audio playback, Bonello diagram, Bolt area, Schröder frequency...)
  
  BULLET::::- Graphical mode calculator
  
  BULLET::::- Standing Waves - Room Modes
   "The hours wore quietly on. The party were dispersed from garret to cellar. At the hour of midnight, as I and two others were crossing the threshold of a room on the second floor, three feminine shrieks rose from the center of the room. Aghast we stood. From all quarters the party rushed… Too brave to desert, yet cowards at heart, we watched the gray light of morning dawn, and each man of us thanked God his night among ghosts was past. After those screams our band was closely knit together… collectively we listened through the waning hours of night to the clanking of sabers and tramping of footfalls."
   Often, the acoustic summing of a room and system are much inferior to the ideal, so the specific relative level will change from −3 dB to 0 dB as the mono signal is panned from center to hard left or right, and this sounds natural. The idea is that when one directs signals left and right with the pan pot, the perceived loudness will stay the same, regardless of latitude.
   This two process model was first proposed in 1982 by Borbely, who called them Process S (homeostatic) and Process C (Circadian) respectively. He showed how the slow wave density increases through the night and then drops off at the beginning of the day while the circadian rhythm is like a sinusoid. He proposed that the pressure to sleep was the maximum when the difference between the two was highest.
  
raw_presuppositions: Sounds heard during the night are much louder than sounds heard during the day. Sounds heard during the night are much louder than sounds heard during the day.
raw_corrections: Sounds heard during the day are covered by many distracting noises, the distracting noises are usually not present at night. This does not actually make noises at night louder than the day. Sounds heard during the day are covered by many distracting noises, the distracting noises are usually not present at night. This does not actually make noises at night louder than the day.