PC Audio: Your Computer's Sound and You

Like so much else on a modern PC, the sound adapter of today is something of a miracle of evolution.

From the very simple speaker chip installed on early PCs producing tinny beeps and simple alarms to a separate expansion board providing a passable ability to both manipulate and send sounds, it's grown into a multi-faceted, multi-device sound adapters able to offer so much resonance and power packed onto a single board. The functions included on the circuit board serving as the basis of a sound adapter include recording, playback, connections for CD and CD audio playback, links to available voice modem technology, special processing to take work away from the potentially over-burdened CPU, and a way to convert analog sound into digital signal, and vice versa.

Psychoacoustics is the study of the human perception of sound. It is used in the development of audio technology including audio hardware and sound compression formulas to help identify what the human ear can and can't register, and what needs "boost" to be heard or "cleaning" to suppress from normal hearing.

Just as with video, the design of audio hardware on a PC or elsewhere in the human environment requires a basic understanding of the principles of human physiology and how it will interpret the output from the device. In this case, it means knowing what sound is and how it is generated, along with the physical properties of the event (the sound) itself.

Sound is produced when an object vibrates and displaces and moves air particles around it. Those air particles begin to collide with the particles around them, and this chain reaction begins to move out, away from the original vibrating object that may drive that air still further by changes in the physical properties of that object (movement of its parts), in something of a pulse-like fashion with vibrations of its own. These vibrations disrupt the air around them as they move, creating waves of fluctuation.

Such vibrations, sent out like the ever-increasing ripple effect of a stone tossed in a body of water, may transmit through solids, gases, or liquids, and at frequencies ranging from 20-20,000 Hz. How much of this we can easily pick up depends, of course, on how acute our hearing is. Some people can detect the simplest and slightest of sounds, while others need to have audio turned up to decibel levels that would deafen the rest of us. For example, like my dog, I can pick up the lightest sounds from far away while my husband, the dear man, usually requires everything to be repeated two or three times at a volume that requires me to scream. However, let's get back to the average human.

When that vibration reaches the human ear, the fluctuating change in air pressure begins to vibrate the eardrum (a slender piece of semi-transparent membrane that separates the outer ear from the middle ear), and the human brain, if all works properly, interprets that motion as sound and registers (consciously or unconsciously) that event.