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Amplitude Envelope

Amplitude is the distance air particles move from their positions of rest as a sound pressure wave propagates. Its psychoacoustic correlate is loudness. When a sound pressure wave is represented as a waveform (see Figure 1), amplitude is the vertical dimension. In Figure 1, the horizontal line represents the position of rest equivalent to atmospheric pressure; the deviations from it above the line represent displacement and positive pressure, and those below it represent displacement and negative pressure. An amplitude envelope can be drawn on a waveform by connecting all the amplitude peaks. Joining the positive peaks creates an upper envelope, and joining the negative ones creates a lower envelope (see Figure 1a).

In most sounds, including speech sounds, the upper and lower envelopes are not exactly ...

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