SVT Octave calculated 1/3,1/6,1/12,1/24

[Sam.Huang]

Hi all

   I want to calculated octave by SVT Fractional-octave Analysis.vi.when Select 1/3 octave out data is right,and other 1/6,1/12,1/24 out data are different,if somewhere was set wrong.Please help me check it,thanks in advance!

[Sam.Huang]

Hi all

   who can help me for that,I want use this octave to generator different sweep sine waveform,It's a appreciated for you help anymore.

[dsb@NI]

Yes, the midband frequencies are different between 1/3 octave and 1/6 octave bands. Refer to Section 5.4 of IEC 61260-1-2014 for the formulas. The SVT VI is returning the correct nominal frequencies for each fractional octave bandwidth according to the standard. 

As a specific example, let us examine the nearest band to 20 Hz.

Full octave: fm = 15.85 Hz, f_nom = 16 Hz

1/3 octave: fm = 19.95 Hz, f_nom = 20 Hz

1/6 octave: fm = 21.13 Hz, f_nom = 21.1 Hz

1/12 octave: fm = 20.54 Hz, f_nom = 20.5 Hz

1/24 octave: fm = 20.24 Hz, f_nom = 20.2 Hz

In the note right below the formulas, IEC 61260 also states:

NOTE 1 The outputs of narrow-bandwidth fractional-octave-band filters that have exact mid-band frequencies
determined from Formula (2) or Formula (3) can be combined to approximate the band level indicated by a filter of
wider bandwidth with a corresponding exact mid-band frequency and corresponding band-edge frequencies.

---

Looking again at 1/6 octave bands, now let us investigate just below 20 Hz:

1/6 octave: fm = 18.84 Hz, f_nom = 18.8 Hz

and we could combine the two 1/6 octave bands around 20 Hz to capture exactly the same band as the 1/3 octave band centered (nominally) at 20 Hz.