Third octave filter
A third octave filter or 1/3 octave filter , also known as a third octave filter , is a specific form of an electrical filter with a constant relative filter width .
The name of this bandpass filter is derived from the fact that its upper cutoff frequency f 2 and its lower cutoff frequency f 1 have the same relationship to one another as an equal major third :
The following applies to the center frequency f 0 of the third-octave filter:
Third octave filters for electroacoustic measurements are standardized according to DIN EN 61260, whereby u. a. the cut-off frequencies f 1 and f 2 , the center frequencies f 0 and the bandwidth B or the quality factor Q are defined, but not the slopes in dB per octave or dB per decade . Most electroacoustic measurements are carried out with filters and standard frequencies of series b according to DIN EN ISO 266, in which f = 1000 Hz occurs as the center frequency.
For sequential third-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 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, electroacoustics - band filters for octaves and fractions of octaves (March 2003)
- DIN EN ISO 266, Acoustics - Standard Frequencies (August 1997)