Octave (electronics)

A frequency ratio expressed in octaves is the base-2 logarithm (binary logarithm) of the ratio: : \text{number of octaves} = \log_2\left(\frac{f_2}{f_1}\right) An amplifier or filter may be stated to have a frequency response of ±6 dB per octave over a particular frequency range, which signifies that the power gain changes by ±6 decibels (a factor of 4 in power), when the frequency changes by a factor of 2. This slope, or more precisely 10 log10(4) ≈ 6 decibels per octave, corresponds to an amplitude gain proportional to frequency, which is equivalent to ±20 dB per decade (factor of 10 amplitude gain change for a factor of 10 frequency change). This would be a first-order filter. ==Example==

The distance between the frequencies 20 Hz and 40 Hz is 1 octave. An amplitude of 52 dB at 4 kHz decreases as frequency increases at −2 dB/oct. What is the amplitude at 13 kHz? : \text{number of octaves} = \log_2\left(\frac{13}{4}\right) = 1.7 : \text{Mag}_{13\text{ kHz}} = 52\text{ dB} + (1.7\text{ oct} \times -2\text{ dB/oct}) = 48.6\text{ dB}.\, ==See also==