programming with max/msp - Virtual Sound

1.2
10
Theory
time (by measuring the pressure at a single location as a function of time). For
example, we can imagine that if we were located at a specific point in space,
we might observe a series of condensations and rarefactions of the air around
us, as in Figure 1.8.
pressure
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Paragraph 1.2 - Frequency, amplitude, and waveform
Fig.1.8 A graphical representation of compression and rarefaction
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At time t -1 , which occurs immediately before t 0, the air pressure has its normal
value, since the cyclic disturbance has not yet reached our point of observation.
At instant t 0, the disturbance arrives at our observation point, pressure starts to
rise, reaches a maximum value at time t 1 , and then decreases until it returns to
normal at time t 2 . It continues to decline, reaching its minimum value at t 3 , after
which pressure returns to its normal value at t 4 ; the pattern then repeats. What
has been described is a phenomenon called a cycle, and an event that always
repeats in this way is called periodic. 8 The time required to complete a cycle is
said to be the period of the wave, which is indicated by the symbol T and is
measured in seconds (s) or in milliseconds (ms). The number of cycles that are
completed in a second is defined as frequency, and is measured in hertz (Hz) or
cycles per second (cps).
If, for example, a sound wave has period T = 0.01s (1/100 of a second), its frequency
will be 1/T = 1/0.01 = 100 Hz (or 100 cycles per second).”(ibid)
While examining Figure 1.9, listen to the sounds of Interactive Example 1A. 9
We can see (and hear) that increasing the number of cycles per second (Hz)
corresponds to making a sound higher in pitch.
8 Mathematically a waveform is said to be periodic if it is repeated regularly for an infinite time. In
the practice of music, of course, we can satisfy ourselves with periods much shorter than infinity!
We will say that a wave is “musically periodic” when it displays enough regularity to induce a
perception of pitch that corresponds to the period of the wave. We’ll discuss this issue in more
detail in Chapter 2.
9 Please note that interactive examples and other supporting materials to the book can be found
on the website.
from “Electronic Music and Sound Design” Vol. 1 by Alessandro Cipriani and Maurizio Giri
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