of Microprocessors

16
Source-SignalAnalys,is
One of the great strengths of digital techniques lies in the ability to
thoroughly analyze already existing sounds. These may either be "natural"
sounds such as musical instruments, speech, animal sounds, etc., or they
may be synthesized sounds. In either case, the goal of analysis is to determine
values of the fundamental parameters that characterize the sound and how
they vary with time.
When the ultimate purpose is synthesis, one may do analysis simply for
education. Certainly, a good understanding of the parameters of existing
sounds will aid in the specification of parameters for similar synthetic
sounds. Often, published literature will have the necessary information, but
it may be obscurely presented or applicable only to generalized or overly
specialized cases. Even when published literature is adequate initially, most
synthesis applications can be expected to gradually specialize beyond its
scope. In either situation, firsthand analysis experience is quite helpful.
The most common application of analysis, however, is in sound modification
in which one obtains data from a natural sound and uses it to direct the
synthesis of an artificial sound. Sometimes the distortions introduced by the
analysis/synthesis process alone are sufficient for the desired results. Usually,
though, the analysis data are modified before the synthesis is performed.
Digital processing of the analysis data can usually be performed such that the
useful information is in an easily usable form. For example, if one wishes to
apply the overall spectral envelope of a particular sound to another sound, a
standard spectral analysis can be smoothed so that details about the individual
harmonics are suppressed but the overall envelope is preserved.
Digital signal analysis is a very broad, very complex topic that keeps
research staffs at many universities busy continuously. It is typically highly
mathematical as well and most literature on the subject is quite obscure
without the necessary training. Although one cannot completely escape such
complexities, an attempt will be made in this chapter to discuss the most
important and easily implemented analysis techniques. While these may not
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