Digital Sound & Music: Concepts, Applications, & Science, Chapter 1, last updated 6/25/2013
1.4 Basic Terminology
1.4.1 Analog vs. Digital
With the evolution of computer technology in the past 50 years, sound processing has become
largely digital. Understanding the difference between analog and digital processes and
phenomena is fundamental to working with sound.
The difference between analog and digital processes runs parallel to the difference
between continuous and discrete number systems. The set of real numbers constitutes a
continuous system, which can be thought of abstractly as an infinite line of continuously
increasing numbers in one direction and decreasing numbers in the other. For any two points on
the line (i.e., real numbers), an infinite number of points exist between them. This is not the case
with discrete number systems, like the set of integers. No integers exist between 1 and 2.
Consecutive integers are completely separate and distinct, which is the basic meaning of
Analog processes and phenomena are similar to continuous number systems. In a time-
based analog phenomenon, one moment of the phenomenon is perceived or measured as moving
continuously into the next. Physical devices can be engineered to behave in a continuous, analog
manner. For example, a volume dial on a radio can be turned left or right continuously. The
diaphragm inside a microphone can move continuously in response to changing air pressure, and
the voltage sent down a wire can change continuously as it records the sound level. However,
communicating continuous data to a computer is a problem. Computers “speak digital,” not
analog. The word digital refers to things that are represented as discrete levels. In the case of
computers, there are exactly two levels – like 0 and 1, or off and on. A two-level system is a
binary system, encodable in a base 2 number system. In contrast to analog processes, digital
processes measure a phenomenon as a sequence of
discrete events encoded in binary.
It could be argued that sound is an inherently
analog phenomenon, the result of waves of changing
air pressure that continuously reach our ears.
However, to be communicated to a computer, the
changes in air pressure must be captured as discrete
events and communicated digitally. When sound
has been encoded in the language that computers
understand, powerful computer-based processing
can be brought to bear on the sound for manipulation
of frequency, dynamic range, phase, and every
imaginable audio property. Thus, we have the
advent of digital signal processing (DSP).
1.4.2 Digital Audio vs. MIDI
This book covers both sampled digital audio and MIDI. Sampled digital audio (or simply
digital audio) consists of streams of audio data that represent the amplitude of sound waves at
discrete moments in time. In the digital recording process, a microphone detects the amplitude
of a sound, thousands of times a second, and sends this information to an audio interface or
sound card in a computer. Each amplitude value is called a sample. The rate at which the
amplitude measurements are recorded by the sound card is called the sampling rate, measured
Aside: One might think, intuitively,
that all physical phenomena are
inherently continuous and thus analog.
But the question of whether the
universe is essentially analog or digital
is actually quite controversial among
physicists and philosophers, a debate
stimulated by the development of
quantum mechanics. Many now view
the universe as operating under a
wave-particle duality and Heisenberg’s
Uncertainty Principle. Related to this
debate is the field of “string theory,”
which the reader may find interesting.