Octave Filters

An octave filter is a filter whose passband covers one octave. An octave is the interval between two frequencies where one frequency is twice the rate of the other.

For example, frequencies of 250 Hz and 500 Hz are one octave apart, as are frequencies of 1 kHz and 2 kHz. The following illustration shows an octave filter, a filter whose passband covers one octave.

Figure 31. Octave Filter Example

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Just as a tuning fork provides a 440 Hz reference frequency for musicians, a reference frequency is needed to fully define octave filters. Instrumentation equipment typically uses a 1 kHz reference frequency.