The Pellucid Sound of Rain

by Gautam Pemmaraju

The Bombay monsoon has finally fallen into character, after a destitute June. As I was falling asleep to the sound of heavy rain a few nights ago, my attention was once again momentarily drawn to the dense ecology of sounds that the droplets made as they struck several surfaces. There was the light, wind-swept tympanic percussion on the window pane, there were the lone droplets on the balcony ledge, the corpulent plops upon the leaves of the potted plants in the balcony, and there was the dense tumescent swoosh, the ‘white noise' of the environment, amidst several discrete sounds of varying time and frequency that I could distinguish in a short audition. Perhaps it was no longer that a few minutes. It felt much longer and so it is when we enter these strange, somewhat unsettling meditative states.

Rain sounds are packaged for commercial use as a sleep therapy device and a mood relaxant. White noise machines are commonly found, and used, although their efficacy is a matter of debate. White noise is generally understood to be a noise signal wherein the entire spectrum of frequencies is at the same intensity. Much like a diaphanous acoustic blanket, the signal has a physical consistency—a sort of drone character, so to speak. The ‘colour of sound', or the ‘colour' of a noise signal is an underlying concept here. Just as in music, we are able to describe and attribute ‘tone colour', what is also known as timbre, to a specific sound. In noise, the colour of a signal refers to the attributes of its frequency spectrum, in particular, its power. White noise is analogous to white light, characterized by a ‘flat frequency spectrum' in a narrow range, and in music and acoustics the signal is understood as a hissing sound. The use of a white noise generator or machine, for whatever purpose one may choose, is a process of ‘sound masking' wherein a sound/noise of the immediate environment is mitigated, cloaked, or ‘masked' by the addition of a natural or artificial sound (such as a white or a pink noise). Generally, the intention is to make the environment more acoustically pleasing, more amenable, relaxed, and to ironically, suggest a sense of quietude. So essentially, in order to mitigate, acoustically shadow, or conceal unwanted sounds that annoy or distract us, we employ noise. In many ways and iterations, we are essentially learning to cope with and negotiate noise (and noises), for noise, is ubiquitous. Actually, we seem to be perpetually learning noise.

Those who work in acoustics and human hearing (not to mention artists such as John Cage) are apt to point out that the search for quietude is actually the search for a bypass to or the absence of “acoustical distractions”, and not in fact, the absence of all sound. Low background noise, and a relative absence of transient sounds would then constitute an acoustic state of ‘quiet'.

In a seminal work for the US Environmental Protection Agency (Kryter, K.D. et al, “The Effects of Noise on People, 1970) the authors point out that during sleep the sense organs are just as responsive to stimuli as they are during a wakeful state, and even during deep sleep information reaches “the highest centers of the brain” (See also this ). Further,

The apparent indifference to stimulation during sleep is not a simple “shutting out” of the neural messages at or near the periphery of the nervous system close to the sense organ. Rather, this apparent indifference to external stimulation is due to a complex reorganization of brain processes during sleeping as opposed to waking states. It is also true that when the eyelids are closed, an ear in on a pillow, or the middle-ear muscles are contracted, responsiveness to the environment can be reduced because the magnitude of the stimulus that reaches the sense organ is not as great. But these physical conditions are no more related to the basic nature of sleep than are reduction of light by eye patches or the attenuation of sound by ear plugs.

Steady, rhythmic sounds, the authors write, may plausibly have a positive effect on sleep. Anecdotal evidence suggests they may have a soothing effect and may also be able to effectively mask out sounds that are distracting. Importantly, they pose a critical question: “Can sleep be induced and maintained by particular rhythms of sound?”

Much like traditional lullabies, it is widely thought that white noise can indeed induce sleep in certain circumstances. In this study on neonates between 2 and 7 days of age, the researchers found that 80% of them fell asleep with the aid of white noise as opposed to only 25% in the control group who fell asleep spontaneously. But white noise does not suppress intrinsic stimuli—if the child is hungry, the application of a white noise machine is unlikely to have any effect. In another study, it was found that patients in ICUs felt they slept better with sound masking intervention, as opposed to those in the control group.

We have all encountered the onomatopoeic whoop-whoop of a ceiling fan on a hot summer's night, or indeed of a hand-fan or punkah; the whirs and drones of refrigerators and air-conditioning, and often enough, the somnolent dance of windshield-wipers whilst driving down a lonesome highway on a cold, miserable, rainy day, seem cunningly to induce us into a devious sleep. The steady rhythms of so very many mundane things we encounter appear to be capable of some kind of sneaky magic. Such is life at times.

The sound of rain however, with its attendant tempers and rhythms, and the mist, light and smell that are by it evoked, either through a synesthesia or through physical phenomena, has always held a special character. Waking up to the sound of a rainstorm very early in the morning, well before sunrise, is a moment that provides a complex sensation of well-being and melancholia at the same time. The sound of rain on the street below as the first milk trucks begin to sputter and rumble in, suggest tragic limits to our collective lives—there is something more, beyond, that we barely grasp.

Aside for lulling us and mostly pleasing our senses, the sound of rain has another, quite significant one might add, practical use. The study of the sound of rain underwater, oceanic rain sounds, of the different kinds of sounds produced by rain striking the surface of the oceans and propagating below contributes critically to scientific study of global rainfall patterns, and thereby weather and climate. The rate of rainfall, the size of raindrops, and other characteristics of rain are collected using underwater rainfall gauges and these recordings provide vital information. As outlined here briefly, the ‘latent heat' that is released each time a raindrop forms, is of particular interest to climatologists, given that this heat is linked to atmospheric circulation. Two distinct components contribute to the sound of a raindrop—the splat impact sound on the surface and the bubble that is formed under the surface during the splash. The bubble is the louder of the two, and interestingly, as indicated here, it in turn has two stages ‘during their lifetimes'—‘”screaming” infant bubbles and quiet adult bubbles.' Due to the differences in pressure within the bubble and outside of it and due to its compensatory oscillation it creates “a distinctive and well-quantified sound.”

Because the sound signatures for each drop size are unique, it is possible to invert the underwater sound field to acoustically estimate the drop size distribution within the rain. Once an acoustic drop size distribution is obtained, a variety of interesting features associated with the rain can be calculated, for example, rainfall rate or median drop size.

(I will mention here the Bathyschape Trieste deep-ocean dive by Jacques Piccard of January 1960. A nagra recorder was used to record oceanic sounds at a depth of over 35,000 feet.)

*

In classical mythologies and literature, there is a great profusion of ideas linked to the sound of rain. A relevant description in this essay draws from the famous play Mṛcchakaṭika by Śudraka, dated between 2 BCE and 5 CE. The erotically charged rendezvous between the principal characters of the play, Vasantasenā and Cārudatta is described in fecund detail here, as the former, the abhisārikā, “braves the rain and thunder…bathetically shattering the wet-sari scene.” As Cārudatta leads his pining lover Vasantasenā into his house, towards the end of the act, we find a description of the sound of the rains, “rather than the normal theatre of the thunder”:

tālīṣu tāraṃ viṭapeṣu mandraṃ śilāsu rūkṣaṃ salileṣu caṇḍam |

saṃgīta-vīṇā iva tāḍyamānās tālā-‘nusāreṇa patanti dhārāḥ ||

A high-pitched plink upon the tāla leaves, a murmuring patter upon the branches, a harsh clatter upon the rocks and a violent crash upon water – the rain falls, keeping the beat, like vīṇās in a concert.

Interestingly, the writer of the above explication on rains, or varṣa, in classical Sanskrit literature, also mentions the various descriptions of clouds, with particular reference to Kalidasa's Meghadūta: “One cloud, with lightning as his torch, roams the world searching for any separated lovers who are still living. And often the clouds are drunkards, full to the brim and charging around dangerously, ready at any moment to spew out their heavy loads.”

Indra, the Vedic god, a demiurge, is regarded as the lord of the firmament with control over the rains, lighting and thunder. He rides a white elephant known as airavata and brandishing vajra, a thunderbolt in one of his hands. He has a fondness for soma , and is known to be a bit of a mischievous and amorous, character—a familiar set of attributes and trope to many of us I daresay. While quite popular at one time, Indra seems to have fallen in stature over the millienia. And as is the case in Hindu myth, there are several other associated deities—from Vidyut, Rudra, Varuna, Atharvan, and then the Maruts and Parjanya. The Maruts, closely associated with Indra, are believed to be the drivers of clouds armed with thunder and lightning. Pugnacious, with lion like roars, they are also meant to be singers offering songs in praise of the heavens. They too appear partial to soma.

Lighting strokes and thunderstorms are linked to lower atmospheric air temperatures and it is generally believed higher temperatures tend to produce more lightning whereas lower do the opposite. Further, the electromagnetic pulses produced by lighting dissipate away from the source; considerable amount of it degrades but some of it, in the very low frequency/long wavelength domain, is able to travel around the earth without much loss. This electromagnetic energy is known as Schumann Resonances. As pointed out here, there is science that links these resonances to global temperatures and here too, there is enough to indicate that there are “positive correlations” between Schumann Resonances and global temperature. Schumann Resonances are considered by some to be a underused barometer; one that has potential to reveal further details, and secrets, of the mysterious ways of our changing/mutating climate.

‘Schumann Resonance' appears here as “revolutionary brain entrainment audio meditation.” Much like Binary Beats, there are many kooky suggestions of the alleged health benefits of natural tones, pure tones, drones, and other manner of repetitive acoustic phenomenon, including white noise.

Whether it be myth, fantasy, popular culture, literature, art, science, or any in-between iteration, random repetitive tones generated by natural phenomenon hold special meaning to my mind. Perhaps as otherworldly drones. Much like the oracular sound of reverberating pre-historic caves, the sound of rain, the complex gush of a tropical storm, is an acoustic experience of transcendent mystery. As I walked to work in the heavy downpour this morning, recalling the deluge of July 2005 in Bombay, and the inscrutable ways of the Indian monsoon, I was momentarily lost again in the thick, unctuous pitter-patter of raindrops on my umbrella. If heard enough, it is easy to get lost in sound.

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