Unit 1: The Nature of Sound and Music

What is Sound?


What is sound? Many of us know that sound has something to do with vibrations — usually in the air, but also possibly in some other medium, such as water.

Sound as Vibrations

These vibrations are rapid alternations in pressure (called compression and rarefaction) that move through the air like waves across the ocean. When a sound begins (a guitar is plucked, a person speaks, a tree falls, etc.), waves of air pressure radiate outward from that source in a manner similar to the way a dropped stone causes concentric ripples in a pond. This can be measured in terms of how many waves pass by each second, expressed in cycles per second (abbreviated cps), now typically called Hertz (abbreviated Hz).

Sound as Perception

But is sound merely vibrations? Or does the definition have something to do with ourselves as well?

The Oxford English Dictionary defines sound as “The sensation produced in the organs of hearing when the surrounding air is set in vibration in such a way as to affect these.” Note that this definition refers first to the sensation, which means that vibrations must be experienced in order to qualify as sound. The OED gives another definition: “That which is or may be heard.” In this sense, it is necessary only that the vibrations may be heard in order to be considered music. Note that both definitions require our actual or potential participation in the process. These definitions — in referring to hearing — also admit that animals participate in the process. But for our purposes, we’ll restrict the remainder of the discussion to humans. In other words, vibrations must be capable of being heard in order to be considered sounds.

Our “organs of hearing,” which include our ears, eardrums, cochlea, etc. (even the brain), are capable of perceiving only certain speeds of vibration as sounds. Vibrations slower than about 15 Hz are usually felt but not heard. Vibrations faster than 20,000 Hz are usually inaudible by humans. But this typical range of human hearing — 15-20,000 Hz — is only an ideal generalization. Many men have a lower high-end threshold than women do. Frequent exposure to loud sounds can lower this upper threshold, and as we age the highest frequency any of us can usually hear drops lower and lower. (This is why the so called “mosquito” ringtone is successful: teenagers can usually hear its 17,000 Hz tone whereas older people cannot.)

 

What all this means is that the definition of sound is somewhat subjective. Sound is what humans can hear, but what humans can hear differs from person to person.

 

What is Sound and Hertz Demo (Video) //Temporary Link

 

The Four Irreducible Features of Sound

There are many ways to describe sounds. Words like beautiful, grating, harmonious, noisy, fast, and sweet often come easily when discussing sounds in general and music in particular. But most of the words we use to describe sounds actually arise from combinations of more basic features (and our reactions to them). The four most basic and irreducible features of sound are these:

• pitch
• duration
• dynamics
• timbre

Every other description you can make of a sound is a product of one or more of these basic features. In this book, we’ll discuss pitch and duration at great length in many units, and learn a little about timbre in Unit 16.

 

Summary video

This material corresponds to UMass OWL Homework 1