Digital Signal Processing Reference
In-Depth Information
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Illustration 55:
On the spectrum of near-periodic sawtooth signals
This series of sawtooth signals illustrates very clearly how often signals should be repeated in order to be
regarded as near-periodic. The upper series also contains a near-periodic signal, because this sawtooth
was only recorded for 1s. Both the lower series include the transition to non-periodic signals.
In practice there are signals which have a linear-like spectrum whose "blurred" lines
cannot in part be interpreted as integer multiples of a basic frequency. They are defined
here as quasi-periodic. The reason why they exist will be described in the next section.
Tones, sounds and music
Up to now we have examined signals which were produced artificially such as rectangu-
lar, sawtooth and even noisy signals. We now come to the signals which are really
meaningful; which are important in an existential sense because they impinge on our
sense organs.
Strangely, in all theoretical topics about Signals-Processes-Systems they are largely
despised or ignored. They do not always fit into simple patterns, they are not just the one
thing but also have characteristics of the other. We are talking here about tones, sounds
and song, but above all about language.
