Representation of Audio Signals
Ian SinclairThe impact that digital methods have made on audio has been at least as remarkable as
it was on computing. Ian Sinclair uses this chapter to introduce the digital methods that
seem so alien to anyone trained in analogue systems.
15.1 Introduction
The term digital audio is used so freely by so many that you could be excused for thinking
there was nothing much new to tell. It is easy in fast conversation to present the impression
of immense knowledge on the subject but it is more diffi cult to express the ideas concisely
yet readably. The range of topics and disciplines that need to be harnessed in order to cover
the fi eld of digital audio is very wide and some of the concepts may appear paradoxical
at fi rst sight. One way of covering the topics would be to go for the apparent precision
of the mathematical statement but, although this has its just place, a simpler physical
understanding of the principles is of greater importance here. Thus in writing this chapter
we steer between excessive arithmetic precision and ambiguous oversimplifi ed description.
15.2 Analogue and Digital ............................................................................................
Many of the physical things that we can sense in our environment appear to us to be part
of a continuous range of sensation. For example, throughout the day much of coastal
England is subject to tides. The cycle of tidal height can be plotted throughout the day.
Imagine a pen plotter marking the height on a drum in much the same way as a barograph
is arranged ( Figure 15.1 ). The continuous line that is plotted is a feature of analogue
signals in which the information is carried as a continuous infi nitely fi ne variation of a
voltage, current, or, as in this case, height of the sea level.
CHAPTER 15