The science of Synthesis Part 3

So far we've looked at how both the pitch and the timbre are determined. The final characteristic to consider is volume.

So far we've looked at how both the pitch and the timbre are determined. The final characteristic to consider is volume. Changes in volume are caused by the amount of air molecules an oscillating object displaces. The more air an object displaces, the louder the perceived sound. This volume also called 'amplitude', is measured by the degree of motion of the air molecules within the sound waves corresponding to the extent of rarefaction and compression that accompanies a wave. The problem, however, is that many simple vibrating objects produce a sound that is inaudible to the human ear because so little air is displaced; therefore for the sound wave to be heard most musical instruments must amplify the sound that's created. To do this, acoustic instruments use the principle of forced vibration that utilizes either a sounding board, as in a piano or similar stringed instruments, or a hollow tube, as in the case of wind instruments.

When a piano string is struck, it's vibrations not only set other strings in motion but also vibrate a board located underneath the strings. Because this sounding board does not share the same frequency as the vibrating wires, the reaction is not very sympathetic and the board is forced to resonate. This resonance moves a large number of air particles than the original sound alone, in effect amplifying the sound. Similarly, when a tuning fork is struck and placed on a tabletop, the table's frequency is forced to match that of the tuning fork and the sound is amplified.

Of course, neither of these methods of amplification offers any physical control over the amplitude. If the level of amplification can be adjusted, then the ration between the original and the changed amplitude is called the 'gain'.

It shoyud be noted, however that loudness itself is difficult to quantify because it's entirely subjective to the listener. Generally speaking, the human ear can detect frequencies from as low as 20Hz up to 20kHz; however, this depends on a number of factors. Indeed, while most of us are capable of hearing (or more accurately feeling) frequencies as low as 20 Hz, the perception of higher frequencies changes with age. Most teenagers are capable of hearing frequencies as high as 18 kHz, while the middle-aged tend not to hear frequencies above 14kHz. A person's level of hearing may also have been damaged, for example by overexposure to loud noise or music. Whether is possible for us to perceive sounds higher than 18kHz with the presence of other sounds is a subject of debate that has yet to be proven. However, it is important to remember that sounds that are between 3 and 5kHz appear perceivably louder than frequencies that are out of this range.

Here concludes the third part of this post, if you want to know more about acoustic science please read. Rick Snoman's Dance Music Manual (Second Edition) Tools, Toys and Techniques.