The most fundamental property of a digital audio signal is its
amplitude. Unfortunately, a signal's amplitude has no one canonical
Strictly speaking, all the samples in a digital audio signal are themselves
amplitudes, and we also spoke of the amplitude of the sinusoid as a whole.
It is useful to have measures
of amplitude for digital audio signals in general. Amplitude
is best thought of as applying to a
window, a fixed range of samples of the signal. For instance, the
window starting at sample of length of an audio signal consists of the
The RMS amplitude of a signal may equal the peak amplitude but never exceeds it; and it may be as little as times the peak amplitude, but never less than that.
Under reasonable conditions--if the window contains at least several periods and if the angular frequency is well under one radian per sample--the peak amplitude of the sinusoid of Page is approximately and its RMS amplitude about . Figure 1.2 shows the peak and RMS amplitudes of two digital audio signals.