Octave Analysis Standards

This topic contains information about the ANSI, IEC, and JIS standards regarding midband frequencies, the nominal frequencies returned by the octave analysis tools in the NI Sound and Vibration Measurement Suite, and compliance with ANSI, IEC, and JIS standards by the octave analysis tools.

Note The octave analysis tools in the Sound and Vibration Measurement Suite use the base 10 system for midband frequencies instead of the base 2 system. Using the base 10 system means that the ratio of two midband frequencies is a fractional power of 10 instead of a fractional power of 2.

According to the IEC 61260:2014 and the ANSI S1.11-2014 standards, the exact mid-band frequencies, fm, of any filter in a set of filters shall be determined from the following expression:

fm = frGx/b, when b is odd

fm = frG(2x + 1)/2b, when b is even

where fr is the reference frequency,

G = 100.3 is the octave frequency ratio,

1/b is the bandwidth designator, and equals 1 for octave, 1/3 for 1/3 octave, 1/6 for 1/6 octave, 1/12 for 1/12 octave, and 1/24 for 1/24 octave,

x is any integer, positive or negative, or zero.

The exact midband frequencies are used to design the filters for fractional-octave analysis. However, all the octave analysis tools in the Sound and Vibration Measurement Suite return the nominal midband frequencies, also called the preferred frequencies. In the case of octave and 1/3 octave analyses, the nominal frequencies are calculated in accordance with the ANSI and IEC standards. In the case of 1/6, 1/12, and 1/24 octave analyses, the nominal frequencies are calculated in accordance with the Annex E (informative) of the IEC 61260:2014 and the ANSI S1.11-2014 standards.

When combined with any National Instruments DSA device, the appropriate microphone, and proper signal conditioning, the filters produced by the octave analysis tools in the Sound and Vibration Measurement Suite comply with the following standards:

  • ANSI S1.11-2014: Electroacoustics - Octave-band and fractional-octave-band filters, class 1
  • IEC 61260:2014: Electroacoustics - Octave-band and fractional-octave-band filters, class 1
  • JIS C 1514:2002: Electroacoustics - Octave-band and fractional-octave-band filters, class 1

For octave filters, choose a sampling frequency at least three times the exact center frequency of the highest frequency band. For fractional-octave filters, choose a sampling frequency at least 2.5 times the exact center frequency of the highest frequency band.