Octave filter

An octave filter is a certain type of filter whose cut-off frequencies are in a constant ratio of 2: 1; see also transmission range .

If the lower limit frequency of the filter is denoted by f ₁ , the following applies to the upper limit frequency f ₂ :

${\displaystyle f_{2}=f_{1}\cdot 2\,}$

and for the filter center frequency :

${\displaystyle f_{0}={\sqrt {f_{1}\cdot f_{2}}}\,}$

Octave filters for electroacoustic measurements are standardized according to DIN EN 61260-1. B. cutoff frequencies f ₁ and f ₂ , center frequency f ₀ bandwidth B or quality factor Q , and not the slope steepnesses are set in dB per octave or dB per decade. Most electroacoustic measurements are carried out with filters and standard frequencies according to DIN EN ISO 266: 1997-08, in which the frequency f = 1000 Hz occurs as the center frequency.

For sequential octave sieve analyzes, filters are offered in which switchable electrical components create new transmission ranges. The electrical settling processes during switching can delay the execution of the analysis more than with octave filters, because more switching processes result in longer settling times. For this reason, parallel filter banks are designed with 1/3 octave filters or with third octave filters . As with octave filters, a single digital third-octave filter can replace such a bank in time division multiplexing without any disadvantage.

literature

• DIN EN 61260-1: 2014-10, electroacoustics - Band filters for octaves and fractions of octaves - Part 1: Requirements (IEC 61260-1: 2014)
• DIN EN ISO 266: 1997-08, Acoustics - standard frequencies (ISO 266: 1997)