By Anjum Altaf
I have been reflecting on the feedback from readers, both negative and positive, and it has helped me immensely to sift through my own biases and prejudices. I am now inclined to drop any remaining pretension to the claim that the end objective of this series is to increase the enjoyment or appreciation of music. This end result may or may not happen but it is not the real driver of this set of notes.
I now realize that I am addressing myself to the set of individuals who wish to talk and write about music, to describe an aural experience in words, and to critique it such that a reader gets a reasonable sense of the difference between one performance and another.
Indian music seems to me like a building suspended in air. The foundations are invisible, not in the sense of their origins (which are well known and well described) but in the sense of their content. This is because familiarization and training in Indian music begins with the music itself – the starting point is always the swaras – Sa, Re, Ga, etc. But what exactly are the swaras? That is not part of the discourse except perhaps to claim that these are the divine sounds favored by the gods.
There is a whole journey from sound to music that is missing in the typical discourse on Indian music. This is what I call the invisible foundation without which we cannot say much about the technical nature of swaras. So this series is also addressed to the set of individuals who are curious about this foundation. And here I am on more certain ground. Knowledge of this foundation should definitely help answer the kinds of questions posed in the fourth installment of this series: What are notes, why there are seven of them, why has every tradition settled on seven notes, what is the relationship among notes, why is one note different from another, what differentiates noise from music, etc.?
These two sets of individuals comprise the audience for this series. If I were to offer this as a course I would call it The Essential Physics of Sound for Curious Musicians and Listeners of Music. (South Asian musicians typically do not study the physics of sound and South Asian students who study the physics of sound are typically not interested in music. There are exceptions, of course, but they have little impact on the traditional teaching of Indian music and are of no benefit to the interested listener.)
In the last installment we had reached the conclusion that there are two key attributes of sound (there are more but we will confine ourselves to these two for the moment). The first is one with which we are very familiar; it defines the volume of sound on the spectrum between soft and loud. The second attribute, still unnamed, helps us identify the difference between sounds (e.g. the difference between the sounds of two bells) and we defined this spectrum to range from gruff to shrill or low to high or flat to sharp sounds. To recapitulate, think of where typical male and female adult voices fall on this spectrum.
I wish we could define this attribute now and move ahead but we can’t because if we do we would be using terms and concepts that are themselves undefined – much like saying that Sa is a swara. We have no choice but to step back and describe how sound is created and how it travels from its source to our ears. I will restrict myself to a skeletal description that would suffice to provide the essential vocabulary needed for this exercise.
The best way to understand how sound is created is to experience it physically. Stretch a rubber band between your thumb and forefinger and pluck it (those who have string instrument like a guitar can use that as a substitute). You will see the rubber band vibrate and also hear a sound. There is a relationship between the two. Very simply, the vibration of the band varies the pressure on the air molecules next it and this pressure wave ripples outwards. If there is a human being in proximity, this wave enters the ear and runs into the ear drum that vibrates in sympathy with the rubber band. We don’t need to know the details of how the vibrations of the ear drum are conveyed to the brain enabling us to hear the sound. (Here you can reflect upon an often posed puzzle: Will there be a sound if a big tree falls in a forest and there is no one to hear it?)
The important point to note is that sound is caused by the vibrations of the source and is transmitted through the air in waves. For an analogy, throw a stone in a pond of water and note the waves that originate from the point of impact and move outwards – you will get a sense of the motion of waves.
A number of details are worth knowing here. First, play around with the rubber band: note the effects of making it less tight while keeping the length the same; varying the length while keeping the tightness constant; changing the thickness of the band while keeping the length and tightness constant; etc. You will note that the sound changes in every case. This is because the vibrations are affected by the length, tightness, and thickness of the band (or string) that is being plucked. Keep this in mind because we will need this when we talk about the tuning of string instruments – how we vary these dimensions to get the sound we want.
Second, and this is both important and interesting, all sound is created by vibrations whether you can see them or not. For example, hit the edge of a drinking glass with a fork and you will hear a sound – the glass vibrated and generated a sound wave although this vibration was not perceptible. One way to convince yourself is to hit the edge of thin brass or copper vessel with a fork and then place a finger on that edge – you will feel the vibration that you did not see. Of course, you will also note that that the glass and the metal produce different sounds – one reason (there are others that we shall come to later) for the difference is that different materials vibrate differently.
Two questions are important at this stage: What is the nature of these sound waves and how rapidly do they travel? We will address these in detail in the next installment but I will leave you with some essentials to motivate the thinking.
First, the speed at which sound travels is a constant (just as the speed of light is constant) – it does not depend upon the source of the sound or how hard the source was plucked or struck. Second, you can imagine the shape of a sound wave by thinking how a child depicts a slithering snake on paper – a lateral continuous S shape with turning points at the peaks and troughs. The more regular the pattern of the wave the more it will tend to music; the less regular it is, the more the sound would tend to noise. Third, the distance between adjacent peaks of the wave pattern (adjacent humps of the slithering snake) will have a lot to do with the flatness or sharpness of the sound heard by the ear.
You can find a useful description of sound waves here along with graphics that show the shape of the wave.