A Swiss-French working group has researched the effects of everyday noise on the development of premature babies' tactile perception.³ Babies were randomly assigned to a loud group and a quiet group, with the noise coming from feeding pump alarms. According to the study, a high noise level not only negatively affects tactile perception but also sensory learning capacity in general. As such, the authors recommend avoiding unnecessary noise in intensive care units to the greatest extent possible, for example by adjusting the alarms on feeding pumps, which typically only indicate the fill level and are not vital.

In spite of these findings, noise is still often excessively loud in the majority of neonatal intensive care units. According to one study, the average NICU noise level throughout the day is Leq = 60.05 dBA and overnight Leq = 58.67 dBA,⁴ with premature babies exposed to frequencies greater than 500 Hz, 57 percent of the time. Other studies have demonstrated that simple actions often produce extreme levels of noise.⁵ Simply setting down an object on the incubator or knocking on the incubator can give rise to extreme levels of noise from 74 to 116 dBA, which can be compared to the level of noise produced by a hammer drill.

In contrast to other units of measure, such as distance or weight, noise can’t be measured on a linear scale – but instead logarithmically. For example, an increase in noise level from 100 to 110 decibels does not represent a ten percent increase, but rather a doubling of the decibel level. Looking at it a different way: under certain conditions, a person is even able to detect a one decibel decrease. Noise is sometimes measured in decibels, shortened to dB, and sometimes in dB(A). In these cases, a process known as A-weighting of the frequencies is carried out and the measurement is weighted. This is applied because higher and lower than normal frequencies are perceived as quieter and therefore given a lower weighting.

There isn’t absolute silence in the womb. From around week 22, a foetus can discern low frequency noises like blood flow, intestinal activity, the mother's voice and ambient sounds such as music, which can reach levels as high as 85 dB.¹⁰ The abdominal wall mutes high frequencies over 200 Hz – while in neonatal units, such noises are common and can occur from things like metal containers, trash bins or loud alarm noises. The ability of an embryo in utero to discern high-frequency noises first develops around week 33 of pregnancy. But such noises in the womb are primarily transmitted through the bones as well as through fluids. Whereas, after birth, noise is transmitted through the air, offering less frequency damping. In addition, the "separating wall" between the embryo and the outside world becomes increasingly thinner as the foetus grows, which exposes the embryo to louder high-frequency noises very gradually. In the event of a premature birth, this gradual adjustment can’t take place, making it all the more essential to avoid loud high-frequency noises in the NICU.¹¹

Many studies show that premature babies respond well to "good" sounds. For example, prematurely born babies are deprived of the rhythm of their mother’s heartbeat, which could explain why very small babies respond well to music. "The Original Sound" study looked at precisely this aspect.¹² The title is the name given to a specifically compiled MP3 file which reproduces sounds like a heart beating, blood flowing through the veins, breathing and other suitable ambient noises. Thirty-four babies were exposed to either these sounds or the normal noises in the intensive care unit for twenty minutes, three times a day. Those babies exposed to the sound file showed a significant reduction in heart rate. This study supports the increasing efforts of music therapists like Haslbeck, who develop supportive measures for premature babies from the 32nd week of gestational age. According to therapy observations, music therapy together with the right care, can promote communication abilities and advance overall development.¹³