In the previous paragraph we saw how the flow of atmospheric pressure in relation to the active loudspeaker can be visualized as a waveform. Waveforms can actually be very complicated, but fortunately every single one of them, and I mean every single one, can be considered as an extension of a very simple wave form: the sinusoid

Sinusoids are the simplest imaginable wave form, and as such is also the least interesting from a sound aesthetics perspective. Let us then make things more interesting for ourselves and complicate them a little. We have said how any wave form is conducible to a combination (sum) of sinusoids with an adequate amplitude and phase

This phenomenon takes place when either the sound source or the listener are moving. The classic example that is always given is the ambulance siren speeding past us and disappearing into the night.

Psychoacoustics studies the brain's sound elaboration mechanisms. A knowledge of such mechanisms is indispensable for the practice of sound engineering, in that it allows, through appropriate manipulation, very sophisticated sound-effects to be obtained.

Factors involved in the localization of a sound source

In this section we'll be looking at the various operations which periodically take place in order to keep a multi-track recorder at its best.

This effect combines the original signal with a delayed version of the latter, where the delay time has been modulated (this means that it varies constantly and the rate of its variations is defined by a function, for example, a sinusoid).

This effect adds light saturations to the input signal. As already mentioned, a saturation generates new harmonics based on the frequency content of the input signal. Therefore, the exciter effect is capable of generating high frequencies out of signals which lack them, as is sometimes the case with vocals which, though being in tune, don't bite enough.

When an elastic system undergoes an oscillating stimulus, it reacts differently depending on the frequency content of the stimulations. In particular, an elastic system will begin to oscillate at the same frequency as the stimulation once the latter is similar his resonance frequency.

When a loudspeaker moves in one direction, creating a compression in front of itself, it also at the same time creates a dilation behind it. The two generated waves would tend to nullify each other, being opposed phase-wise, and this would impede the diffusion of the acoustic-wave into the environment.