Amplitude and Intensity

[Hanzhang X]

What’s the relationship between amplitude and intensity? Are they basically the same? The unit for intensity is dB, and how about amplitude?

[Simon]

When we look at a waveform, what we are seeing is amplitude on the vertical axis. Intensity is proportional to amplitude squared. Intensity is a measure of the energy that this waveform is carrying.

We don’t need to get hung up on this. Although amplitude does have units (it is the sound pressure, which has units of Newtons per square metre), we don’t usually write these units on the vertical axis of a waveform. That’s because our microphone and soundcard are not calibrated.

It’s also important to remember that neither amplitude nor intensity are the same thing as loudness, which is a perceptual phenomenon and varies with the frequency of the sound.

[Dimitra L]

When we talk about magnitude do we mean intensity or amplitude ?

[Simon]

The term magnitude is usually used with regard to the spectrum (e.g., obtained by the FFT). It is used to distinguish from the phase spectrum, which we don’t really need to worry about here.

[Author]

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