Page "Bandwidth (signal processing)" Paragraph 6

For different applications there are different precise definitions.

For example, one definition of bandwidth could be the range of frequencies beyond which the frequency function is zero.

This would correspond to the mathematical notion of the support of a function ( i. e., the total " length " of values for which the function is nonzero ).

A less strict and more practically useful definition will refer to the frequencies where the frequency function is small.

Small could mean less than 3 dB below ( i. e., power output < 1 / 2 or voltage output < 0. 707 of ) the maximum value, or more rarely 10 dB below, or it could mean below a certain absolute value.

As with any definition of the width of a function, many definitions are suitable for different purposes.