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Get the list of valid ANSI S1.11-2004 center frequencies



centerFrequencies = getANSICenterFrequencies(octFilt) returns a vector of valid center frequencies as specified by the ANSI S1.11-2004 standard.


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Create an object of the octaveFilter System object™. Call getANSICenterFrequencies to get a list of valid center frequencies.

octFilt = octaveFilter;
centerFrequencies = getANSICenterFrequencies(octFilt)
centerFrequencies = 1×15
103 ×

    0.0005    0.0010    0.0020    0.0040    0.0079    0.0158    0.0316    0.0631    0.1259    0.2512    0.5012    1.0000    1.9953    3.9811    7.9433

Input Arguments

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Object of the octaveFilter System object™.

Output Arguments

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Center frequencies specified by the ANSI S1.11-2004 standard, returned as a vector.

The range for computing valid center frequencies is 3 Hz to (Fs/2) Hz, where the SampleRate property of your octave filter defines Fs.

Data Types: single | double


The ANSI S1.11-2004 standard [1] defines the center frequencies of the octave bands as

fc={fr×G(k30)/b,b is oddfr×G(2k59)/2b,b is even


  • fr is the reference frequency, 1000 Hz.

  • G is the octave ratio, 100.3.

  • b is the number of bands per octave, which is the inverse of the bandwidth of the filter in octaves. Specify the bandwidth using the Bandwidth property of octFilt.

  • k is any integer and represents the band number.

The center frequency definition differs depending on whether b is odd, such as for bandwidths of 1 octave or 1/3 octave, or even, such as for bandwidths of 1/2 octave or 1/6 octave. This ensures that the band edges of the whole octave band remain band edges for all of the fractional bands.

Diagram showing how the band edges of whole octave bands align with band edges in one-third and one-half octave bands. The center frequencies in the one-half octave bands do not align with the center frequencies in the whole or one-third octave bands.


[1] Acoustical Society of America. American National Standard Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters. ANSI S1.11-2004. Melville, NY: Acoustical Society of America, 2009.

Version History

Introduced in R2016b